Merge branch 'release-0.4.0'

28 files changed, 3253 insertions, 2272 deletions

diff --git a/.builds/archlinux-msrv.yml b/.builds/archlinux-msrv.yml
new file mode 100644
index 0000000..66c0390
--- /dev/null
+++ b/.builds/archlinux-msrv.yml
@@ -0,0 +1,22 @@
+# Copyright (C) 2019 Robin Krahl <robin.krahl@ireas.org>
+# SPDX-License-Identifier: CC0-1.0
+image: archlinux
+packages:
+  - rustup
+  - libnitrokey
+environment:
+  USE_SYSTEM_LIBNITROKEY: "1"
+sources:
+  - https://git.ireas.org/nitrokey-rs
+tasks:
+  - setup: |
+      rustup set profile minimal
+      rustup default 1.34.2
+  - version: |
+      rustc -V
+  - build: |
+      cd nitrokey-rs
+      cargo build --release
+  - test: |
+      cd nitrokey-rs
+      cargo test
diff --git a/.builds/archlinux-use-system-lib.yaml b/.builds/archlinux-use-system-lib.yml
index 01705c1..29bda19 100644
--- a/.builds/archlinux-use-system-lib.yaml
+++ b/.builds/archlinux-use-system-lib.yml
@@ -1,3 +1,5 @@
+# Copyright (C) 2019 Robin Krahl <robin.krahl@ireas.org>
+# SPDX-License-Identifier: CC0-1.0
 image: archlinux
 packages:
   - rust
@@ -7,6 +9,8 @@ environment:
 sources:
   - https://git.ireas.org/nitrokey-rs
 tasks:
+  - version: |
+      rustc -V
   - build: |
       cd nitrokey-rs
       cargo build --release
@@ -16,3 +20,6 @@ tasks:
   - format: |
       cd nitrokey-rs
       cargo fmt -- --check
+  - clippy: |
+      cd nitrokey-rs
+      cargo clippy -- -D warnings
diff --git a/.builds/archlinux.yml b/.builds/archlinux.yml
index 543e93c..151eb66 100644
--- a/.builds/archlinux.yml
+++ b/.builds/archlinux.yml
@@ -1,3 +1,5 @@
+# Copyright (C) 2019 Robin Krahl <robin.krahl@ireas.org>
+# SPDX-License-Identifier: CC0-1.0
 image: archlinux
 packages:
   - rust
@@ -12,6 +14,3 @@ tasks:
   - test: |
       cd nitrokey-rs
       cargo test
-  - format: |
-      cd nitrokey-rs
-      cargo fmt -- --check
diff --git a/.builds/lint.yml b/.builds/lint.yml
new file mode 100644
index 0000000..678cde8
--- /dev/null
+++ b/.builds/lint.yml
@@ -0,0 +1,16 @@
+# Copyright (C) 2019 Robin Krahl <robin.krahl@ireas.org>
+# SPDX-License-Identifier: CC0-1.0
+image: archlinux
+packages:
+  - gnupg
+  - reuse
+sources:
+  - https://git.ireas.org/nitrokey-rs
+tasks:
+  - verify: |
+      cd nitrokey-rs
+      curl -s "https://pgp.ireas.org/0x6D533958F070C57C.txt" | gpg --import
+      git verify-commit HEAD
+  - reuse: |
+      cd nitrokey-rs
+      reuse lint
diff --git a/.gitignore b/.gitignore
index 4cdf3b3..7ea18df 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,5 @@
-
+# Copyright (C) 2019 Robin Krahl <robin.krahl@ireas.org>
+# SPDX-License-Identifier: CC0-1.0
 /target
 /nitrokey-sys/target
 **/*.rs.bk
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 04da117..d4451bc 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,58 @@
+<!---
+Copyright (C) 2019-2020 Robin Krahl <robin.krahl@ireas.org>
+SPDX-License-Identifier: CC0-1.0
+-->
+
+# v0.4.0 (2020-01-02)
+- Remove the `test-pro` and `test-storage` features.
+- Implement `Display` for `Version`.
+- Introduce `DEFAULT_ADMIN_PIN` and `DEFAULT_USER_PIN` constants.
+- Refactor the error handling code:
+  - Implement `std::error::Error` for `CommandError`.
+  - Add the `Error` enum.
+  - Add the `LibraryError` enum and move the library error variants from
+    `CommandError` to `LibraryError`.
+  - Add the `CommunicationError` enum and move the communication error variants
+    from `CommandError` to `CommunicationError`.
+  - Return `Error` instead of `CommandError` in all public functions.
+  - Move the `CommandError::RngError` variant to `Error::RandError` and the
+    `CommandError::Unknown` variant to `Error::UnknownError`.
+  - Return `CommunicationError::NotConnected` instead of
+    `CommandError::Undefined` from the connect functions.
+  - Remove the `CommandError::Undefined` variant.
+- Add a private `PhantomData` field to `Pro` and `Storage` to make direct
+  instantiation impossible.
+- Refactor and clean up internal code:
+  - Prefer using the `Into` trait over numeric casting.
+  - Add `Pro::new` and `Storage::new` functions.
+- Implement `From<Pro>` and `From<Storage>` for `DeviceWrapper`.
+- Add `Error::Utf8Error` variant.
+  - Return `Result<Version>` instead of `Version` from `get_library_version`.
+  - Return `Error::Utf8Error` if libnitrokey returns an invalid UTF-8 string.
+- Implement `From<(T: Device, Error)>` for `Error`.
+- Fix timing issues with the `totp_no_pin` and `totp_pin` test cases.
+- Always return a `Result` in functions that communicate with a device.
+- Combine `get_{major,minor}_firmware_version` into `get_firmware_version`.
+- Add `set_encrypted_volume_mode` to `Storage`.
+- Use mutability to represent changes to the device status:
+  - Implement `DerefMut` for `User<T>` and `Admin<T>`.
+  - Add `device_mut` method to `DeviceWrapper`.
+  - Require a mutable `Device` reference if a method changes the device state.
+- Update dependencies:
+  - `nitrokey-sys` to 3.5
+  - `nitrokey-test` to 0.3
+  - `rand_core` to 0.5
+  - `rand_os` to 0.2
+- Add `nitrokey-test-state` dependency in version 0.1.
+- Refactor connection management:
+  - Add `ConcurrentAccessError` and `PoisonError` `Error` variants.
+  - Add the `Manager` struct that manages connections to Nitrokey devices.
+  - Remove `connect`, `connect_model`, `Pro::connect` and `Storage::connect`.
+  - Add the `into_manager` function to the `Device` trait.
+  - Add the `force_take` function that ignores a `PoisonError` when accessing
+    the manager instance.
+- Internally refactor the `device` module into submodules.
+
 # v0.3.5 (2019-12-16)
 - Update the nitrokey-sys dependency version specification to ~3.4.
 
diff --git a/Cargo.toml b/Cargo.toml
index 238cc02..b57591b 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,9 @@
+# Copyright (C) 2019-2020 Robin Krahl <robin.krahl@ireas.org>
+# SPDX-License-Identifier: CC0-1.0
+
 [package]
 name = "nitrokey"
-version = "0.3.5"
+version = "0.4.0"
 authors = ["Robin Krahl <robin.krahl@ireas.org>"]
 edition = "2018"
 homepage = "https://code.ireas.org/nitrokey-rs/"
@@ -11,16 +14,14 @@ keywords = ["nitrokey", "otp"]
 categories = ["api-bindings"]
 readme = "README.md"
 license = "MIT"
-
-[features]
-test-pro = []
-test-storage = []
+exclude = [".builds/*"]
 
 [dependencies]
+lazy_static = "1.2"
 libc = "0.2"
-nitrokey-sys = "~3.4"
-rand_core = {version = "0.3", default-features = false}
-rand_os = {version = "0.1"}
+nitrokey-sys = "3.5"
+rand_core = {version = "0.5.1", features = ["getrandom"] }
 
 [dev-dependencies]
-nitrokey-test = {version = "0.1"}
+nitrokey-test = "0.3"
+nitrokey-test-state = "0.1"
diff --git a/LICENSES/CC0-1.0.txt b/LICENSES/CC0-1.0.txt
new file mode 100644
index 0000000..0e259d4
--- /dev/null
+++ b/LICENSES/CC0-1.0.txt
@@ -0,0 +1,121 @@
+Creative Commons Legal Code
+
+CC0 1.0 Universal
+
+    CREATIVE COMMONS CORPORATION IS NOT A LAW FIRM AND DOES NOT PROVIDE
+    LEGAL SERVICES. DISTRIBUTION OF THIS DOCUMENT DOES NOT CREATE AN
+    ATTORNEY-CLIENT RELATIONSHIP. CREATIVE COMMONS PROVIDES THIS
+    INFORMATION ON AN "AS-IS" BASIS. CREATIVE COMMONS MAKES NO WARRANTIES
+    REGARDING THE USE OF THIS DOCUMENT OR THE INFORMATION OR WORKS
+    PROVIDED HEREUNDER, AND DISCLAIMS LIABILITY FOR DAMAGES RESULTING FROM
+    THE USE OF THIS DOCUMENT OR THE INFORMATION OR WORKS PROVIDED
+    HEREUNDER.
+
+Statement of Purpose
+
+The laws of most jurisdictions throughout the world automatically confer
+exclusive Copyright and Related Rights (defined below) upon the creator
+and subsequent owner(s) (each and all, an "owner") of an original work of
+authorship and/or a database (each, a "Work").
+
+Certain owners wish to permanently relinquish those rights to a Work for
+the purpose of contributing to a commons of creative, cultural and
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+works, reuse and redistribute as freely as possible in any form whatsoever
+and for any purposes, including without limitation commercial purposes.
+These owners may contribute to the Commons to promote the ideal of a free
+culture and the further production of creative, cultural and scientific
+works, or to gain reputation or greater distribution for their Work in
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+
+For these and/or other purposes and motivations, and without any
+expectation of additional consideration or compensation, the person
+associating CC0 with a Work (the "Affirmer"), to the extent that he or she
+is an owner of Copyright and Related Rights in the Work, voluntarily
+elects to apply CC0 to the Work and publicly distribute the Work under its
+terms, with knowledge of his or her Copyright and Related Rights in the
+Work and the meaning and intended legal effect of CC0 on those rights.
+
+1. Copyright and Related Rights. A Work made available under CC0 may be
+protected by copyright and related or neighboring rights ("Copyright and
+Related Rights"). Copyright and Related Rights include, but are not
+limited to, the following:
+
+  i. the right to reproduce, adapt, distribute, perform, display,
+     communicate, and translate a Work;
+ ii. moral rights retained by the original author(s) and/or performer(s);
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+ iv. rights protecting against unfair competition in regards to a Work,
+     subject to the limitations in paragraph 4(a), below;
+  v. rights protecting the extraction, dissemination, use and reuse of data
+     in a Work;
+ vi. database rights (such as those arising under Directive 96/9/EC of the
+     European Parliament and of the Council of 11 March 1996 on the legal
+     protection of databases, and under any national implementation
+     thereof, including any amended or successor version of such
+     directive); and
+vii. other similar, equivalent or corresponding rights throughout the
+     world based on applicable law or treaty, and any national
+     implementations thereof.
+
+2. Waiver. To the greatest extent permitted by, but not in contravention
+of, applicable law, Affirmer hereby overtly, fully, permanently,
+irrevocably and unconditionally waives, abandons, and surrenders all of
+Affirmer's Copyright and Related Rights and associated claims and causes
+of action, whether now known or unknown (including existing as well as
+future claims and causes of action), in the Work (i) in all territories
+worldwide, (ii) for the maximum duration provided by applicable law or
+treaty (including future time extensions), (iii) in any current or future
+medium and for any number of copies, and (iv) for any purpose whatsoever,
+including without limitation commercial, advertising or promotional
+purposes (the "Waiver"). Affirmer makes the Waiver for the benefit of each
+member of the public at large and to the detriment of Affirmer's heirs and
+successors, fully intending that such Waiver shall not be subject to
+revocation, rescission, cancellation, termination, or any other legal or
+equitable action to disrupt the quiet enjoyment of the Work by the public
+as contemplated by Affirmer's express Statement of Purpose.
+
+3. Public License Fallback. Should any part of the Waiver for any reason
+be judged legally invalid or ineffective under applicable law, then the
+Waiver shall be preserved to the maximum extent permitted taking into
+account Affirmer's express Statement of Purpose. In addition, to the
+extent the Waiver is so judged Affirmer hereby grants to each affected
+person a royalty-free, non transferable, non sublicensable, non exclusive,
+irrevocable and unconditional license to exercise Affirmer's Copyright and
+Related Rights in the Work (i) in all territories worldwide, (ii) for the
+maximum duration provided by applicable law or treaty (including future
+time extensions), (iii) in any current or future medium and for any number
+of copies, and (iv) for any purpose whatsoever, including without
+limitation commercial, advertising or promotional purposes (the
+"License"). The License shall be deemed effective as of the date CC0 was
+applied by Affirmer to the Work. Should any part of the License for any
+reason be judged legally invalid or ineffective under applicable law, such
+partial invalidity or ineffectiveness shall not invalidate the remainder
+of the License, and in such case Affirmer hereby affirms that he or she
+will not (i) exercise any of his or her remaining Copyright and Related
+Rights in the Work or (ii) assert any associated claims and causes of
+action with respect to the Work, in either case contrary to Affirmer's
+express Statement of Purpose.
+
+4. Limitations and Disclaimers.
+
+ a. No trademark or patent rights held by Affirmer are waived, abandoned,
+    surrendered, licensed or otherwise affected by this document.
+ b. Affirmer offers the Work as-is and makes no representations or
+    warranties of any kind concerning the Work, express, implied,
+    statutory or otherwise, including without limitation warranties of
+    title, merchantability, fitness for a particular purpose, non
+    infringement, or the absence of latent or other defects, accuracy, or
+    the present or absence of errors, whether or not discoverable, all to
+    the greatest extent permissible under applicable law.
+ c. Affirmer disclaims responsibility for clearing rights of other persons
+    that may apply to the Work or any use thereof, including without
+    limitation any person's Copyright and Related Rights in the Work.
+    Further, Affirmer disclaims responsibility for obtaining any necessary
+    consents, permissions or other rights required for any use of the
+    Work.
+ d. Affirmer understands and acknowledges that Creative Commons is not a
+    party to this document and has no duty or obligation with respect to
+    this CC0 or use of the Work.
diff --git a/LICENSE b/LICENSES/MIT.txt
index 1a3601d..6c67cd5 100644
--- a/LICENSE
+++ b/LICENSES/MIT.txt
@@ -1,3 +1,6 @@
+Valid-License-Identifier: MIT
+License-Text:
+
 The MIT License (MIT)
 
 Copyright (c) 2018 Robin Krahl <robin.krahl@ireas.org>
diff --git a/README.md b/README.md
index 567ae58..12a9f6d 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,8 @@
+<!---
+Copyright (C) 2019 Robin Krahl <robin.krahl@ireas.org>
+SPDX-License-Identifier: CC0-1.0
+-->
+
 # nitrokey-rs
 
 A libnitrokey wrapper for Rust providing access to Nitrokey devices.
@@ -23,19 +28,18 @@ supported by `nitrokey-rs`:
 
 - `NK_get_device_model`.  We know which model we connected to, so we can
   provide this information without calling `libnitrokey`.
-- `NK_get_time`.  This method is useless as it will always cause a timestamp
-  error on the device (see [pull request #114][] for `libnitrokey` for details).
-- `NK_get_status`.  This method only provides a string representation of
-  data that can be accessed by other methods (firmware version, serial number,
-  configuration).
-- `NK_get_status_storage_as_string`.  This method only provides an incomplete
-  string representation of the data returned by `NK_get_status_storage`.
+- `NK_is_AES_supported`.  This method is no longer needed for Nitrokey devices
+  with a recent firmware version.
 - `NK_set_unencrypted_volume_rorw_pin_type_user`,
-  `NK_set_unencrypted_read_only`, `NK_set_unencrypted_read_write`,
-  `NK_set_encrypted_read_only` and `NK_set_encrypted_read_write`.  These
+  `NK_set_unencrypted_read_only`, `NK_set_unencrypted_read_write`.  These
   methods are only relevant for older firmware versions (pre-v0.51).  As the
   Nitrokey Storage firmware can be updated easily, we do not support these
   outdated versions.
+- `NK_totp_get_time`, `NK_status`.  These functions are deprecated.
+- `NK_read_HOTP_slot`.  This function is only available for HOTP slots, not for
+  TOTP.  We will support it once both types are supported by `libnitrokey`.
+- All `*_as_string` functions that return string representations of data
+  returned by other functions.
 
 ## Tests
 
@@ -51,16 +55,18 @@ Note that the tests assume that the device’s passwords are the factory default
 (admin PIN `12345678`, user PIN `123456`, update password `12345678`) and that
 an AES key has been built.  Some tests will overwrite the data stored on the
 Nitrokey device or perform a factory reset.  Never execute the tests if you
-unless yout want to destroy all data on all connected Nitrokey devices!
-
-The `totp_no_pin` and `totp_pin` tests can occasionally fail due to bad timing.
+don’t want to destroy all data on any connected Nitrokey device!
 
 ## Acknowledgments
 
-Thanks to Nitrokey UG for providing a Nitrokey Storage to support the
+Thanks to Nitrokey UG for providing two Nitrokey devices to support the
 development of this crate.  Thanks to Daniel Mueller for contributions to
 `nitrokey-rs` and for the `nitrokey-test` crate.
 
+## Minimum Supported Rust Version
+
+This crate supports Rust 1.34.2 or later.
+
 ## Contact
 
 For bug reports, patches, feature requests or other messages, please send a
@@ -68,14 +74,19 @@ mail to [nitrokey-rs-dev@ireas.org][].
 
 ## License
 
-This project is licensed under the [MIT License][].  `libnitrokey` is licensed
-under the [LGPL-3.0][].
+This project is licensed under the [MIT][] license.  The documentation and
+configuration files contained in this repository are licensed under the
+[Creative Commons Zero][CC0] license.  You can find a copy of the license texts
+in the `LICENSES` directory.  `libnitrokey` is licensed under the [LGPL-3.0][].
+
+`nitrokey-rs` complies with [version 3.0 of the REUSE specification][reuse].
 
 [Documentation]: https://docs.rs/nitrokey
 [Nitrokey udev rules]: https://www.nitrokey.com/documentation/frequently-asked-questions-faq#openpgp-card-not-available
 [`libnitrokey`]: https://github.com/nitrokey/libnitrokey
 [`nitrokey-test`]: https://github.com/d-e-s-o/nitrokey-test
 [nitrokey-rs-dev@ireas.org]: mailto:nitrokey-rs-dev@ireas.org
-[pull request #114]: https://github.com/Nitrokey/libnitrokey/pull/114
-[MIT license]: https://opensource.org/licenses/MIT
+[MIT]: https://opensource.org/licenses/MIT
+[CC0]: https://creativecommons.org/publicdomain/zero/1.0/
 [LGPL-3.0]: https://opensource.org/licenses/lgpl-3.0.html
+[reuse]: https://reuse.software/practices/3.0/
diff --git a/TODO.md b/TODO.md
index 28bd3b8..54525ef 100644
--- a/TODO.md
+++ b/TODO.md
@@ -1,18 +1,22 @@
+<!---
+Copyright (C) 2019 Robin Krahl <robin.krahl@ireas.org>
+SPDX-License-Identifier: CC0-1.0
+-->
+
 - Add support for the currently unsupported commands:
-    - `NK_is_AES_supported`
     - `NK_send_startup`
     - `NK_fill_SD_card_with_random_data`
-    - `NK_get_SD_usage_data_as_string`
+    - `NK_get_SD_usage_data`
     - `NK_get_progress_bar_value`
     - `NK_list_devices_by_cpuID`
     - `NK_connect_with_ID`
-- Fix timing issues with the `totp_no_pin` and `totp_pin` test cases.
+    - `NK_get_status`
+    - `NK_list_devices`
+    - `NK_free_device_info`
+    - `NK_connect_with_path`
+    - `NK_enable_firmware_update_pro`
+    - `NK_change_firmware_password_pro`
 - Clear passwords from memory.
-- Find a nicer syntax for the `write_config` test.
-- Prevent construction of internal types.
-- More specific error checking in the tests.
-- Check integer conversions.
-- Consider implementing `Into<CommandError>` for `(Device, CommandError)`
 - Lock password safe in `PasswordSafe::drop()` (see [nitrokey-storage-firmware
   issue 65][]).
 - Disable creation of multiple password safes at the same time.
diff --git a/src/auth.rs b/src/auth.rs
index 2d61d4b..cab1021 100644
--- a/src/auth.rs
+++ b/src/auth.rs
@@ -1,4 +1,9 @@
-use std::ops::Deref;
+// Copyright (C) 2018-2019 Robin Krahl <robin.krahl@ireas.org>
+// SPDX-License-Identifier: MIT
+
+use std::convert::TryFrom as _;
+use std::marker;
+use std::ops;
 use std::os::raw::c_char;
 use std::os::raw::c_int;
 
@@ -6,17 +11,16 @@ use nitrokey_sys;
 
 use crate::config::{Config, RawConfig};
 use crate::device::{Device, DeviceWrapper, Pro, Storage};
+use crate::error::Error;
 use crate::otp::{ConfigureOtp, GenerateOtp, OtpMode, OtpSlotData, RawOtpSlotData};
-use crate::util::{
-    generate_password, get_command_result, get_cstring, result_from_string, CommandError,
-};
+use crate::util::{generate_password, get_command_result, get_cstring, result_from_string};
 
 static TEMPORARY_PASSWORD_LENGTH: usize = 25;
 
 /// Provides methods to authenticate as a user or as an admin using a PIN.  The authenticated
 /// methods will consume the current device instance.  On success, they return the authenticated
 /// device.  Otherwise, they return the current unauthenticated device and the error code.
-pub trait Authenticate {
+pub trait Authenticate<'a> {
     /// Performs user authentication.  This method consumes the device.  If successful, an
     /// authenticated device is returned.  Otherwise, the current unauthenticated device and the
     /// error are returned.
@@ -34,20 +38,21 @@ pub trait Authenticate {
     ///
     /// ```no_run
     /// use nitrokey::{Authenticate, DeviceWrapper, User};
-    /// # use nitrokey::CommandError;
+    /// # use nitrokey::Error;
     ///
-    /// fn perform_user_task(device: &User<DeviceWrapper>) {}
+    /// fn perform_user_task<'a>(device: &User<'a, DeviceWrapper<'a>>) {}
     /// fn perform_other_task(device: &DeviceWrapper) {}
     ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let device = manager.connect()?;
     /// let device = match device.authenticate_user("123456") {
     ///     Ok(user) => {
     ///         perform_user_task(&user);
     ///         user.device()
     ///     },
     ///     Err((device, err)) => {
-    ///         println!("Could not authenticate as user: {}", err);
+    ///         eprintln!("Could not authenticate as user: {}", err);
     ///         device
     ///     },
     /// };
@@ -56,12 +61,12 @@ pub trait Authenticate {
     /// # }
     /// ```
     ///
-    /// [`InvalidString`]: enum.CommandError.html#variant.InvalidString
+    /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     /// [`RngError`]: enum.CommandError.html#variant.RngError
     /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    fn authenticate_user(self, password: &str) -> Result<User<Self>, (Self, CommandError)>
+    fn authenticate_user(self, password: &str) -> Result<User<'a, Self>, (Self, Error)>
     where
-        Self: Device + Sized;
+        Self: Device<'a> + Sized;
 
     /// Performs admin authentication.  This method consumes the device.  If successful, an
     /// authenticated device is returned.  Otherwise, the current unauthenticated device and the
@@ -80,20 +85,21 @@ pub trait Authenticate {
     ///
     /// ```no_run
     /// use nitrokey::{Authenticate, Admin, DeviceWrapper};
-    /// # use nitrokey::CommandError;
+    /// # use nitrokey::Error;
     ///
-    /// fn perform_admin_task(device: &Admin<DeviceWrapper>) {}
+    /// fn perform_admin_task<'a>(device: &Admin<'a, DeviceWrapper<'a>>) {}
     /// fn perform_other_task(device: &DeviceWrapper) {}
     ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let device = manager.connect()?;
     /// let device = match device.authenticate_admin("123456") {
     ///     Ok(admin) => {
     ///         perform_admin_task(&admin);
     ///         admin.device()
     ///     },
     ///     Err((device, err)) => {
-    ///         println!("Could not authenticate as admin: {}", err);
+    ///         eprintln!("Could not authenticate as admin: {}", err);
     ///         device
     ///     },
     /// };
@@ -102,16 +108,18 @@ pub trait Authenticate {
     /// # }
     /// ```
     ///
-    /// [`InvalidString`]: enum.CommandError.html#variant.InvalidString
+    /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     /// [`RngError`]: enum.CommandError.html#variant.RngError
     /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    fn authenticate_admin(self, password: &str) -> Result<Admin<Self>, (Self, CommandError)>
+    fn authenticate_admin(self, password: &str) -> Result<Admin<'a, Self>, (Self, Error)>
     where
-        Self: Device + Sized;
+        Self: Device<'a> + Sized;
 }
 
 trait AuthenticatedDevice<T> {
     fn new(device: T, temp_password: Vec<u8>) -> Self;
+
+    fn temp_password_ptr(&self) -> *const c_char;
 }
 
 /// A Nitrokey device with user authentication.
@@ -124,9 +132,10 @@ trait AuthenticatedDevice<T> {
 /// [`authenticate_admin`]: trait.Authenticate.html#method.authenticate_admin
 /// [`device`]: #method.device
 #[derive(Debug)]
-pub struct User<T: Device> {
+pub struct User<'a, T: Device<'a>> {
     device: T,
     temp_password: Vec<u8>,
+    marker: marker::PhantomData<&'a T>,
 }
 
 /// A Nitrokey device with admin authentication.
@@ -139,14 +148,15 @@ pub struct User<T: Device> {
 /// [`authenticate_admin`]: trait.Authenticate.html#method.authenticate_admin
 /// [`device`]: #method.device
 #[derive(Debug)]
-pub struct Admin<T: Device> {
+pub struct Admin<'a, T: Device<'a>> {
     device: T,
     temp_password: Vec<u8>,
+    marker: marker::PhantomData<&'a T>,
 }
 
-fn authenticate<D, A, T>(device: D, password: &str, callback: T) -> Result<A, (D, CommandError)>
+fn authenticate<'a, D, A, T>(device: D, password: &str, callback: T) -> Result<A, (D, Error)>
 where
-    D: Device,
+    D: Device<'a>,
     A: AuthenticatedDevice<D>,
     T: Fn(*const c_char, *const c_char) -> c_int,
 {
@@ -160,20 +170,20 @@ where
     };
     let password_ptr = password.as_ptr();
     let temp_password_ptr = temp_password.as_ptr() as *const c_char;
-    return match callback(password_ptr, temp_password_ptr) {
+    match callback(password_ptr, temp_password_ptr) {
         0 => Ok(A::new(device, temp_password)),
-        rv => Err((device, CommandError::from(rv))),
-    };
+        rv => Err((device, Error::from(rv))),
+    }
 }
 
-fn authenticate_user_wrapper<T, C>(
+fn authenticate_user_wrapper<'a, T, C>(
     device: T,
     constructor: C,
     password: &str,
-) -> Result<User<DeviceWrapper>, (DeviceWrapper, CommandError)>
+) -> Result<User<'a, DeviceWrapper<'a>>, (DeviceWrapper<'a>, Error)>
 where
-    T: Device,
-    C: Fn(T) -> DeviceWrapper,
+    T: Device<'a> + 'a,
+    C: Fn(T) -> DeviceWrapper<'a>,
 {
     let result = device.authenticate_user(password);
     match result {
@@ -182,14 +192,14 @@ where
     }
 }
 
-fn authenticate_admin_wrapper<T, C>(
+fn authenticate_admin_wrapper<'a, T, C>(
     device: T,
     constructor: C,
     password: &str,
-) -> Result<Admin<DeviceWrapper>, (DeviceWrapper, CommandError)>
+) -> Result<Admin<'a, DeviceWrapper<'a>>, (DeviceWrapper<'a>, Error)>
 where
-    T: Device,
-    C: Fn(T) -> DeviceWrapper,
+    T: Device<'a> + 'a,
+    C: Fn(T) -> DeviceWrapper<'a>,
 {
     let result = device.authenticate_admin(password);
     match result {
@@ -198,7 +208,7 @@ where
     }
 }
 
-impl<T: Device> User<T> {
+impl<'a, T: Device<'a>> User<'a, T> {
     /// Forgets the user authentication and returns an unauthenticated device.  This method
     /// consumes the authenticated device.  It does not perform any actual commands on the
     /// Nitrokey.
@@ -207,7 +217,7 @@ impl<T: Device> User<T> {
     }
 }
 
-impl<T: Device> Deref for User<T> {
+impl<'a, T: Device<'a>> ops::Deref for User<'a, T> {
     type Target = T;
 
     fn deref(&self) -> &Self::Target {
@@ -215,38 +225,41 @@ impl<T: Device> Deref for User<T> {
     }
 }
 
-impl<T: Device> GenerateOtp for User<T> {
-    fn get_hotp_code(&self, slot: u8) -> Result<String, CommandError> {
-        unsafe {
-            let temp_password_ptr = self.temp_password.as_ptr() as *const c_char;
-            return result_from_string(nitrokey_sys::NK_get_hotp_code_PIN(slot, temp_password_ptr));
-        }
+impl<'a, T: Device<'a>> ops::DerefMut for User<'a, T> {
+    fn deref_mut(&mut self) -> &mut T {
+        &mut self.device
     }
+}
 
-    fn get_totp_code(&self, slot: u8) -> Result<String, CommandError> {
-        unsafe {
-            let temp_password_ptr = self.temp_password.as_ptr() as *const c_char;
-            return result_from_string(nitrokey_sys::NK_get_totp_code_PIN(
-                slot,
-                0,
-                0,
-                0,
-                temp_password_ptr,
-            ));
-        }
+impl<'a, T: Device<'a>> GenerateOtp for User<'a, T> {
+    fn get_hotp_code(&mut self, slot: u8) -> Result<String, Error> {
+        result_from_string(unsafe {
+            nitrokey_sys::NK_get_hotp_code_PIN(slot, self.temp_password_ptr())
+        })
+    }
+
+    fn get_totp_code(&self, slot: u8) -> Result<String, Error> {
+        result_from_string(unsafe {
+            nitrokey_sys::NK_get_totp_code_PIN(slot, 0, 0, 0, self.temp_password_ptr())
+        })
     }
 }
 
-impl<T: Device> AuthenticatedDevice<T> for User<T> {
+impl<'a, T: Device<'a>> AuthenticatedDevice<T> for User<'a, T> {
     fn new(device: T, temp_password: Vec<u8>) -> Self {
         User {
             device,
             temp_password,
+            marker: marker::PhantomData,
         }
     }
+
+    fn temp_password_ptr(&self) -> *const c_char {
+        self.temp_password.as_ptr() as *const c_char
+    }
 }
 
-impl<T: Device> Deref for Admin<T> {
+impl<'a, T: Device<'a>> ops::Deref for Admin<'a, T> {
     type Target = T;
 
     fn deref(&self) -> &Self::Target {
@@ -254,7 +267,13 @@ impl<T: Device> Deref for Admin<T> {
     }
 }
 
-impl<T: Device> Admin<T> {
+impl<'a, T: Device<'a>> ops::DerefMut for Admin<'a, T> {
+    fn deref_mut(&mut self) -> &mut T {
+        &mut self.device
+    }
+}
+
+impl<'a, T: Device<'a>> Admin<'a, T> {
     /// Forgets the user authentication and returns an unauthenticated device.  This method
     /// consumes the authenticated device.  It does not perform any actual commands on the
     /// Nitrokey.
@@ -272,50 +291,43 @@ impl<T: Device> Admin<T> {
     ///
     /// ```no_run
     /// use nitrokey::{Authenticate, Config};
-    /// # use nitrokey::CommandError;
+    /// # use nitrokey::Error;
     ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let device = manager.connect()?;
     /// let config = Config::new(None, None, None, false);
     /// match device.authenticate_admin("12345678") {
-    ///     Ok(admin) => {
+    ///     Ok(mut admin) => {
     ///         admin.write_config(config);
     ///         ()
     ///     },
-    ///     Err((_, err)) => println!("Could not authenticate as admin: {}", err),
+    ///     Err((_, err)) => eprintln!("Could not authenticate as admin: {}", err),
     /// };
     /// #     Ok(())
     /// # }
     /// ```
     ///
-    /// [`InvalidSlot`]: enum.CommandError.html#variant.InvalidSlot
-    pub fn write_config(&self, config: Config) -> Result<(), CommandError> {
+    /// [`InvalidSlot`]: enum.LibraryError.html#variant.InvalidSlot
+    pub fn write_config(&mut self, config: Config) -> Result<(), Error> {
         let raw_config = RawConfig::try_from(config)?;
-        unsafe {
-            get_command_result(nitrokey_sys::NK_write_config(
+        get_command_result(unsafe {
+            nitrokey_sys::NK_write_config(
                 raw_config.numlock,
                 raw_config.capslock,
                 raw_config.scrollock,
                 raw_config.user_password,
                 false,
-                self.temp_password.as_ptr() as *const c_char,
-            ))
-        }
-    }
-
-    fn write_otp_slot<C>(&self, data: OtpSlotData, callback: C) -> Result<(), CommandError>
-    where
-        C: Fn(RawOtpSlotData, *const c_char) -> c_int,
-    {
-        let raw_data = RawOtpSlotData::new(data)?;
-        let temp_password_ptr = self.temp_password.as_ptr() as *const c_char;
-        get_command_result(callback(raw_data, temp_password_ptr))
+                self.temp_password_ptr(),
+            )
+        })
     }
 }
 
-impl<T: Device> ConfigureOtp for Admin<T> {
-    fn write_hotp_slot(&self, data: OtpSlotData, counter: u64) -> Result<(), CommandError> {
-        self.write_otp_slot(data, |raw_data: RawOtpSlotData, temp_password_ptr| unsafe {
+impl<'a, T: Device<'a>> ConfigureOtp for Admin<'a, T> {
+    fn write_hotp_slot(&mut self, data: OtpSlotData, counter: u64) -> Result<(), Error> {
+        let raw_data = RawOtpSlotData::new(data)?;
+        get_command_result(unsafe {
             nitrokey_sys::NK_write_hotp_slot(
                 raw_data.number,
                 raw_data.name.as_ptr(),
@@ -325,13 +337,14 @@ impl<T: Device> ConfigureOtp for Admin<T> {
                 raw_data.use_enter,
                 raw_data.use_token_id,
                 raw_data.token_id.as_ptr(),
-                temp_password_ptr,
+                self.temp_password_ptr(),
             )
         })
     }
 
-    fn write_totp_slot(&self, data: OtpSlotData, time_window: u16) -> Result<(), CommandError> {
-        self.write_otp_slot(data, |raw_data: RawOtpSlotData, temp_password_ptr| unsafe {
+    fn write_totp_slot(&mut self, data: OtpSlotData, time_window: u16) -> Result<(), Error> {
+        let raw_data = RawOtpSlotData::new(data)?;
+        get_command_result(unsafe {
             nitrokey_sys::NK_write_totp_slot(
                 raw_data.number,
                 raw_data.name.as_ptr(),
@@ -341,33 +354,40 @@ impl<T: Device> ConfigureOtp for Admin<T> {
                 raw_data.use_enter,
                 raw_data.use_token_id,
                 raw_data.token_id.as_ptr(),
-                temp_password_ptr,
+                self.temp_password_ptr(),
             )
         })
     }
 
-    fn erase_hotp_slot(&self, slot: u8) -> Result<(), CommandError> {
-        let temp_password_ptr = self.temp_password.as_ptr() as *const c_char;
-        unsafe { get_command_result(nitrokey_sys::NK_erase_hotp_slot(slot, temp_password_ptr)) }
+    fn erase_hotp_slot(&mut self, slot: u8) -> Result<(), Error> {
+        get_command_result(unsafe {
+            nitrokey_sys::NK_erase_hotp_slot(slot, self.temp_password_ptr())
+        })
     }
 
-    fn erase_totp_slot(&self, slot: u8) -> Result<(), CommandError> {
-        let temp_password_ptr = self.temp_password.as_ptr() as *const c_char;
-        unsafe { get_command_result(nitrokey_sys::NK_erase_totp_slot(slot, temp_password_ptr)) }
+    fn erase_totp_slot(&mut self, slot: u8) -> Result<(), Error> {
+        get_command_result(unsafe {
+            nitrokey_sys::NK_erase_totp_slot(slot, self.temp_password_ptr())
+        })
     }
 }
 
-impl<T: Device> AuthenticatedDevice<T> for Admin<T> {
+impl<'a, T: Device<'a>> AuthenticatedDevice<T> for Admin<'a, T> {
     fn new(device: T, temp_password: Vec<u8>) -> Self {
         Admin {
             device,
             temp_password,
+            marker: marker::PhantomData,
         }
     }
+
+    fn temp_password_ptr(&self) -> *const c_char {
+        self.temp_password.as_ptr() as *const c_char
+    }
 }
 
-impl Authenticate for DeviceWrapper {
-    fn authenticate_user(self, password: &str) -> Result<User<Self>, (Self, CommandError)> {
+impl<'a> Authenticate<'a> for DeviceWrapper<'a> {
+    fn authenticate_user(self, password: &str) -> Result<User<'a, Self>, (Self, Error)> {
         match self {
             DeviceWrapper::Storage(storage) => {
                 authenticate_user_wrapper(storage, DeviceWrapper::Storage, password)
@@ -376,7 +396,7 @@ impl Authenticate for DeviceWrapper {
         }
     }
 
-    fn authenticate_admin(self, password: &str) -> Result<Admin<Self>, (Self, CommandError)> {
+    fn authenticate_admin(self, password: &str) -> Result<Admin<'a, Self>, (Self, Error)> {
         match self {
             DeviceWrapper::Storage(storage) => {
                 authenticate_admin_wrapper(storage, DeviceWrapper::Storage, password)
@@ -388,28 +408,28 @@ impl Authenticate for DeviceWrapper {
     }
 }
 
-impl Authenticate for Pro {
-    fn authenticate_user(self, password: &str) -> Result<User<Self>, (Self, CommandError)> {
+impl<'a> Authenticate<'a> for Pro<'a> {
+    fn authenticate_user(self, password: &str) -> Result<User<'a, Self>, (Self, Error)> {
         authenticate(self, password, |password_ptr, temp_password_ptr| unsafe {
             nitrokey_sys::NK_user_authenticate(password_ptr, temp_password_ptr)
         })
     }
 
-    fn authenticate_admin(self, password: &str) -> Result<Admin<Self>, (Self, CommandError)> {
+    fn authenticate_admin(self, password: &str) -> Result<Admin<'a, Self>, (Self, Error)> {
         authenticate(self, password, |password_ptr, temp_password_ptr| unsafe {
             nitrokey_sys::NK_first_authenticate(password_ptr, temp_password_ptr)
         })
     }
 }
 
-impl Authenticate for Storage {
-    fn authenticate_user(self, password: &str) -> Result<User<Self>, (Self, CommandError)> {
+impl<'a> Authenticate<'a> for Storage<'a> {
+    fn authenticate_user(self, password: &str) -> Result<User<'a, Self>, (Self, Error)> {
         authenticate(self, password, |password_ptr, temp_password_ptr| unsafe {
             nitrokey_sys::NK_user_authenticate(password_ptr, temp_password_ptr)
         })
     }
 
-    fn authenticate_admin(self, password: &str) -> Result<Admin<Self>, (Self, CommandError)> {
+    fn authenticate_admin(self, password: &str) -> Result<Admin<'a, Self>, (Self, Error)> {
         authenticate(self, password, |password_ptr, temp_password_ptr| unsafe {
             nitrokey_sys::NK_first_authenticate(password_ptr, temp_password_ptr)
         })
diff --git a/src/config.rs b/src/config.rs
index 2ce6f77..cb678d7 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -1,4 +1,9 @@
-use crate::util::CommandError;
+// Copyright (C) 2018-2019 Robin Krahl <robin.krahl@ireas.org>
+// SPDX-License-Identifier: MIT
+
+use std::convert;
+
+use crate::error::{Error, LibraryError};
 
 /// The configuration for a Nitrokey.
 #[derive(Clone, Copy, Debug, PartialEq)]
@@ -30,21 +35,21 @@ pub struct RawConfig {
 
 fn config_otp_slot_to_option(value: u8) -> Option<u8> {
     if value < 3 {
-        return Some(value);
+        Some(value)
+    } else {
+        None
     }
-    None
 }
 
-fn option_to_config_otp_slot(value: Option<u8>) -> Result<u8, CommandError> {
-    match value {
-        Some(value) => {
-            if value < 3 {
-                Ok(value)
-            } else {
-                Err(CommandError::InvalidSlot)
-            }
+fn option_to_config_otp_slot(value: Option<u8>) -> Result<u8, Error> {
+    if let Some(value) = value {
+        if value < 3 {
+            Ok(value)
+        } else {
+            Err(LibraryError::InvalidSlot.into())
         }
-        None => Ok(255),
+    } else {
+        Ok(255)
     }
 }
 
@@ -65,8 +70,10 @@ impl Config {
     }
 }
 
-impl RawConfig {
-    pub fn try_from(config: Config) -> Result<RawConfig, CommandError> {
+impl convert::TryFrom<Config> for RawConfig {
+    type Error = Error;
+
+    fn try_from(config: Config) -> Result<RawConfig, Error> {
         Ok(RawConfig {
             numlock: option_to_config_otp_slot(config.numlock)?,
             capslock: option_to_config_otp_slot(config.capslock)?,
diff --git a/src/device.rs b/src/device.rs
deleted file mode 100644
index 9813c50..0000000
--- a/src/device.rs
+++ /dev/null
@@ -1,1367 +0,0 @@
-use std::fmt;
-
-use libc;
-use nitrokey_sys;
-
-use crate::auth::Authenticate;
-use crate::config::{Config, RawConfig};
-use crate::otp::GenerateOtp;
-use crate::pws::GetPasswordSafe;
-use crate::util::{
-    get_command_result, get_cstring, get_last_error, result_from_string, CommandError,
-};
-
-/// Available Nitrokey models.
-#[derive(Clone, Copy, Debug, PartialEq)]
-pub enum Model {
-    /// The Nitrokey Storage.
-    Storage,
-    /// The Nitrokey Pro.
-    Pro,
-}
-
-impl fmt::Display for Model {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(
-            f,
-            "{}",
-            match *self {
-                Model::Pro => "Pro",
-                Model::Storage => "Storage",
-            }
-        )
-    }
-}
-
-/// The access mode of a volume on the Nitrokey Storage.
-#[derive(Clone, Copy, Debug, PartialEq)]
-pub enum VolumeMode {
-    /// A read-only volume.
-    ReadOnly,
-    /// A read-write volume.
-    ReadWrite,
-}
-
-impl fmt::Display for VolumeMode {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match *self {
-            VolumeMode::ReadOnly => f.write_str("read-only"),
-            VolumeMode::ReadWrite => f.write_str("read-write"),
-        }
-    }
-}
-
-/// A wrapper for a Nitrokey device of unknown type.
-///
-/// Use the function [`connect`][] to obtain a wrapped instance.  The wrapper implements all traits
-/// that are shared between all Nitrokey devices so that the shared functionality can be used
-/// without knowing the type of the underlying device.  If you want to use functionality that is
-/// not available for all devices, you have to extract the device.
-///
-/// # Examples
-///
-/// Authentication with error handling:
-///
-/// ```no_run
-/// use nitrokey::{Authenticate, DeviceWrapper, User};
-/// # use nitrokey::CommandError;
-///
-/// fn perform_user_task(device: &User<DeviceWrapper>) {}
-/// fn perform_other_task(device: &DeviceWrapper) {}
-///
-/// # fn try_main() -> Result<(), CommandError> {
-/// let device = nitrokey::connect()?;
-/// let device = match device.authenticate_user("123456") {
-///     Ok(user) => {
-///         perform_user_task(&user);
-///         user.device()
-///     },
-///     Err((device, err)) => {
-///         println!("Could not authenticate as user: {}", err);
-///         device
-///     },
-/// };
-/// perform_other_task(&device);
-/// #     Ok(())
-/// # }
-/// ```
-///
-/// Device-specific commands:
-///
-/// ```no_run
-/// use nitrokey::{DeviceWrapper, Storage};
-/// # use nitrokey::CommandError;
-///
-/// fn perform_common_task(device: &DeviceWrapper) {}
-/// fn perform_storage_task(device: &Storage) {}
-///
-/// # fn try_main() -> Result<(), CommandError> {
-/// let device = nitrokey::connect()?;
-/// perform_common_task(&device);
-/// match device {
-///     DeviceWrapper::Storage(storage) => perform_storage_task(&storage),
-///     _ => (),
-/// };
-/// #     Ok(())
-/// # }
-/// ```
-///
-/// [`connect`]: fn.connect.html
-#[derive(Debug)]
-pub enum DeviceWrapper {
-    /// A Nitrokey Storage device.
-    Storage(Storage),
-    /// A Nitrokey Pro device.
-    Pro(Pro),
-}
-
-/// A Nitrokey Pro device without user or admin authentication.
-///
-/// Use the global function [`connect`][] to obtain an instance wrapper or the method
-/// [`connect`][`Pro::connect`] to directly obtain an instance.  If you want to execute a command
-/// that requires user or admin authentication, use [`authenticate_admin`][] or
-/// [`authenticate_user`][].
-///
-/// # Examples
-///
-/// Authentication with error handling:
-///
-/// ```no_run
-/// use nitrokey::{Authenticate, User, Pro};
-/// # use nitrokey::CommandError;
-///
-/// fn perform_user_task(device: &User<Pro>) {}
-/// fn perform_other_task(device: &Pro) {}
-///
-/// # fn try_main() -> Result<(), CommandError> {
-/// let device = nitrokey::Pro::connect()?;
-/// let device = match device.authenticate_user("123456") {
-///     Ok(user) => {
-///         perform_user_task(&user);
-///         user.device()
-///     },
-///     Err((device, err)) => {
-///         println!("Could not authenticate as user: {}", err);
-///         device
-///     },
-/// };
-/// perform_other_task(&device);
-/// #     Ok(())
-/// # }
-/// ```
-///
-/// [`authenticate_admin`]: trait.Authenticate.html#method.authenticate_admin
-/// [`authenticate_user`]: trait.Authenticate.html#method.authenticate_user
-/// [`connect`]: fn.connect.html
-/// [`Pro::connect`]: #method.connect
-#[derive(Debug)]
-pub struct Pro {}
-
-/// A Nitrokey Storage device without user or admin authentication.
-///
-/// Use the global function [`connect`][] to obtain an instance wrapper or the method
-/// [`connect`][`Storage::connect`] to directly obtain an instance.  If you want to execute a
-/// command that requires user or admin authentication, use [`authenticate_admin`][] or
-/// [`authenticate_user`][].
-///
-/// # Examples
-///
-/// Authentication with error handling:
-///
-/// ```no_run
-/// use nitrokey::{Authenticate, User, Storage};
-/// # use nitrokey::CommandError;
-///
-/// fn perform_user_task(device: &User<Storage>) {}
-/// fn perform_other_task(device: &Storage) {}
-///
-/// # fn try_main() -> Result<(), CommandError> {
-/// let device = nitrokey::Storage::connect()?;
-/// let device = match device.authenticate_user("123456") {
-///     Ok(user) => {
-///         perform_user_task(&user);
-///         user.device()
-///     },
-///     Err((device, err)) => {
-///         println!("Could not authenticate as user: {}", err);
-///         device
-///     },
-/// };
-/// perform_other_task(&device);
-/// #     Ok(())
-/// # }
-/// ```
-///
-/// [`authenticate_admin`]: trait.Authenticate.html#method.authenticate_admin
-/// [`authenticate_user`]: trait.Authenticate.html#method.authenticate_user
-/// [`connect`]: fn.connect.html
-/// [`Storage::connect`]: #method.connect
-#[derive(Debug)]
-pub struct Storage {}
-
-/// The status of a volume on a Nitrokey Storage device.
-#[derive(Debug)]
-pub struct VolumeStatus {
-    /// Indicates whether the volume is read-only.
-    pub read_only: bool,
-    /// Indicates whether the volume is active.
-    pub active: bool,
-}
-
-/// Information about the SD card in a Storage device.
-#[derive(Debug)]
-pub struct SdCardData {
-    /// The serial number of the SD card.
-    pub serial_number: u32,
-    /// The size of the SD card in GB.
-    pub size: u8,
-    /// The year the card was manufactured, e. g. 17 for 2017.
-    pub manufacturing_year: u8,
-    /// The month the card was manufactured.
-    pub manufacturing_month: u8,
-    /// The OEM ID.
-    pub oem: u16,
-    /// The manufacturer ID.
-    pub manufacturer: u8,
-}
-
-#[derive(Debug)]
-/// Production information for a Storage device.
-pub struct StorageProductionInfo {
-    /// The major firmware version, e. g. 0 in v0.40.
-    pub firmware_version_major: u8,
-    /// The minor firmware version, e. g. 40 in v0.40.
-    pub firmware_version_minor: u8,
-    /// The internal firmware version.
-    pub firmware_version_internal: u8,
-    /// The serial number of the CPU.
-    pub serial_number_cpu: u32,
-    /// Information about the SD card.
-    pub sd_card: SdCardData,
-}
-
-/// The status of a Nitrokey Storage device.
-#[derive(Debug)]
-pub struct StorageStatus {
-    /// The status of the unencrypted volume.
-    pub unencrypted_volume: VolumeStatus,
-    /// The status of the encrypted volume.
-    pub encrypted_volume: VolumeStatus,
-    /// The status of the hidden volume.
-    pub hidden_volume: VolumeStatus,
-    /// The major firmware version, e. g. 0 in v0.40.
-    pub firmware_version_major: u8,
-    /// The minor firmware version, e. g. 40 in v0.40.
-    pub firmware_version_minor: u8,
-    /// Indicates whether the firmware is locked.
-    pub firmware_locked: bool,
-    /// The serial number of the SD card in the Storage stick.
-    pub serial_number_sd_card: u32,
-    /// The serial number of the smart card in the Storage stick.
-    pub serial_number_smart_card: u32,
-    /// The number of remaining login attempts for the user PIN.
-    pub user_retry_count: u8,
-    /// The number of remaining login attempts for the admin PIN.
-    pub admin_retry_count: u8,
-    /// Indicates whether a new SD card was found.
-    pub new_sd_card_found: bool,
-    /// Indicates whether the SD card is filled with random characters.
-    pub filled_with_random: bool,
-    /// Indicates whether the stick has been initialized by generating
-    /// the AES keys.
-    pub stick_initialized: bool,
-}
-
-/// A Nitrokey device.
-///
-/// This trait provides the commands that can be executed without authentication and that are
-/// present on all supported Nitrokey devices.
-pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp {
-    /// Returns the model of the connected Nitrokey device.
-    ///
-    /// # Example
-    ///
-    /// ```no_run
-    /// use nitrokey::Device;
-    /// # use nitrokey::CommandError;
-    ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
-    /// println!("Connected to a Nitrokey {}", device.get_model());
-    /// #    Ok(())
-    /// # }
-    fn get_model(&self) -> Model;
-
-    /// Returns the serial number of the Nitrokey device.  The serial number is the string
-    /// representation of a hex number.
-    ///
-    /// # Example
-    ///
-    /// ```no_run
-    /// use nitrokey::Device;
-    /// # use nitrokey::CommandError;
-    ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
-    /// match device.get_serial_number() {
-    ///     Ok(number) => println!("serial no: {}", number),
-    ///     Err(err) => println!("Could not get serial number: {}", err),
-    /// };
-    /// #     Ok(())
-    /// # }
-    /// ```
-    fn get_serial_number(&self) -> Result<String, CommandError> {
-        unsafe { result_from_string(nitrokey_sys::NK_device_serial_number()) }
-    }
-
-    /// Returns the number of remaining authentication attempts for the user.  The total number of
-    /// available attempts is three.
-    ///
-    /// # Example
-    ///
-    /// ```no_run
-    /// use nitrokey::Device;
-    /// # use nitrokey::CommandError;
-    ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
-    /// let count = device.get_user_retry_count();
-    /// println!("{} remaining authentication attempts (user)", count);
-    /// #     Ok(())
-    /// # }
-    /// ```
-    fn get_user_retry_count(&self) -> u8 {
-        unsafe { nitrokey_sys::NK_get_user_retry_count() }
-    }
-
-    /// Returns the number of remaining authentication attempts for the admin.  The total number of
-    /// available attempts is three.
-    ///
-    /// # Example
-    ///
-    /// ```no_run
-    /// use nitrokey::Device;
-    /// # use nitrokey::CommandError;
-    ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
-    /// let count = device.get_admin_retry_count();
-    /// println!("{} remaining authentication attempts (admin)", count);
-    /// #     Ok(())
-    /// # }
-    /// ```
-    fn get_admin_retry_count(&self) -> u8 {
-        unsafe { nitrokey_sys::NK_get_admin_retry_count() }
-    }
-
-    /// Returns the major part of the firmware version (should be zero).
-    ///
-    /// # Example
-    ///
-    /// ```no_run
-    /// use nitrokey::Device;
-    /// # use nitrokey::CommandError;
-    ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
-    /// println!(
-    ///     "Firmware version: {}.{}",
-    ///     device.get_major_firmware_version(),
-    ///     device.get_minor_firmware_version(),
-    /// );
-    /// #     Ok(())
-    /// # }
-    /// ```
-    fn get_major_firmware_version(&self) -> i32 {
-        unsafe { nitrokey_sys::NK_get_major_firmware_version() }
-    }
-
-    /// Returns the minor part of the firmware version (for example 8 for version 0.8).
-    ///
-    /// # Example
-    ///
-    /// ```no_run
-    /// use nitrokey::Device;
-    /// # use nitrokey::CommandError;
-    ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
-    /// println!(
-    ///     "Firmware version: {}.{}",
-    ///     device.get_major_firmware_version(),
-    ///     device.get_minor_firmware_version(),
-    /// );
-    /// #     Ok(())
-    /// # }
-    fn get_minor_firmware_version(&self) -> i32 {
-        unsafe { nitrokey_sys::NK_get_minor_firmware_version() }
-    }
-
-    /// Returns the current configuration of the Nitrokey device.
-    ///
-    /// # Example
-    ///
-    /// ```no_run
-    /// use nitrokey::Device;
-    /// # use nitrokey::CommandError;
-    ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
-    /// let config = device.get_config()?;
-    /// println!("numlock binding:          {:?}", config.numlock);
-    /// println!("capslock binding:         {:?}", config.capslock);
-    /// println!("scrollock binding:        {:?}", config.scrollock);
-    /// println!("require password for OTP: {:?}", config.user_password);
-    /// #     Ok(())
-    /// # }
-    /// ```
-    fn get_config(&self) -> Result<Config, CommandError> {
-        unsafe {
-            let config_ptr = nitrokey_sys::NK_read_config();
-            if config_ptr.is_null() {
-                return Err(get_last_error());
-            }
-            let config_array_ptr = config_ptr as *const [u8; 5];
-            let raw_config = RawConfig::from(*config_array_ptr);
-            libc::free(config_ptr as *mut libc::c_void);
-            return Ok(raw_config.into());
-        }
-    }
-
-    /// Changes the administrator PIN.
-    ///
-    /// # Errors
-    ///
-    /// - [`InvalidString`][] if one of the provided passwords contains a null byte
-    /// - [`WrongPassword`][] if the current admin password is wrong
-    ///
-    /// # Example
-    ///
-    /// ```no_run
-    /// use nitrokey::Device;
-    /// # use nitrokey::CommandError;
-    ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
-    /// match device.change_admin_pin("12345678", "12345679") {
-    ///     Ok(()) => println!("Updated admin PIN."),
-    ///     Err(err) => println!("Failed to update admin PIN: {}", err),
-    /// };
-    /// #     Ok(())
-    /// # }
-    /// ```
-    ///
-    /// [`InvalidString`]: enum.CommandError.html#variant.InvalidString
-    /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    fn change_admin_pin(&self, current: &str, new: &str) -> Result<(), CommandError> {
-        let current_string = get_cstring(current)?;
-        let new_string = get_cstring(new)?;
-        unsafe {
-            get_command_result(nitrokey_sys::NK_change_admin_PIN(
-                current_string.as_ptr(),
-                new_string.as_ptr(),
-            ))
-        }
-    }
-
-    /// Changes the user PIN.
-    ///
-    /// # Errors
-    ///
-    /// - [`InvalidString`][] if one of the provided passwords contains a null byte
-    /// - [`WrongPassword`][] if the current user password is wrong
-    ///
-    /// # Example
-    ///
-    /// ```no_run
-    /// use nitrokey::Device;
-    /// # use nitrokey::CommandError;
-    ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
-    /// match device.change_user_pin("123456", "123457") {
-    ///     Ok(()) => println!("Updated admin PIN."),
-    ///     Err(err) => println!("Failed to update admin PIN: {}", err),
-    /// };
-    /// #     Ok(())
-    /// # }
-    /// ```
-    ///
-    /// [`InvalidString`]: enum.CommandError.html#variant.InvalidString
-    /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    fn change_user_pin(&self, current: &str, new: &str) -> Result<(), CommandError> {
-        let current_string = get_cstring(current)?;
-        let new_string = get_cstring(new)?;
-        unsafe {
-            get_command_result(nitrokey_sys::NK_change_user_PIN(
-                current_string.as_ptr(),
-                new_string.as_ptr(),
-            ))
-        }
-    }
-
-    /// Unlocks the user PIN after three failed login attempts and sets it to the given value.
-    ///
-    /// # Errors
-    ///
-    /// - [`InvalidString`][] if one of the provided passwords contains a null byte
-    /// - [`WrongPassword`][] if the admin password is wrong
-    ///
-    /// # Example
-    ///
-    /// ```no_run
-    /// use nitrokey::Device;
-    /// # use nitrokey::CommandError;
-    ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
-    /// match device.unlock_user_pin("12345678", "123456") {
-    ///     Ok(()) => println!("Unlocked user PIN."),
-    ///     Err(err) => println!("Failed to unlock user PIN: {}", err),
-    /// };
-    /// #     Ok(())
-    /// # }
-    /// ```
-    ///
-    /// [`InvalidString`]: enum.CommandError.html#variant.InvalidString
-    /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    fn unlock_user_pin(&self, admin_pin: &str, user_pin: &str) -> Result<(), CommandError> {
-        let admin_pin_string = get_cstring(admin_pin)?;
-        let user_pin_string = get_cstring(user_pin)?;
-        unsafe {
-            get_command_result(nitrokey_sys::NK_unlock_user_password(
-                admin_pin_string.as_ptr(),
-                user_pin_string.as_ptr(),
-            ))
-        }
-    }
-
-    /// Locks the Nitrokey device.
-    ///
-    /// This disables the password store if it has been unlocked.  On the Nitrokey Storage, this
-    /// also disables the volumes if they have been enabled.
-    ///
-    /// # Example
-    ///
-    /// ```no_run
-    /// use nitrokey::Device;
-    /// # use nitrokey::CommandError;
-    ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
-    /// match device.lock() {
-    ///     Ok(()) => println!("Locked the Nitrokey device."),
-    ///     Err(err) => println!("Could not lock the Nitrokey device: {}", err),
-    /// };
-    /// #     Ok(())
-    /// # }
-    /// ```
-    fn lock(&self) -> Result<(), CommandError> {
-        unsafe { get_command_result(nitrokey_sys::NK_lock_device()) }
-    }
-
-    /// Performs a factory reset on the Nitrokey device.
-    ///
-    /// This commands performs a factory reset on the smart card (like the factory reset via `gpg
-    /// --card-edit`) and then clears the flash memory (password safe, one-time passwords etc.).
-    /// After a factory reset, [`build_aes_key`][] has to be called before the password safe or the
-    /// encrypted volume can be used.
-    ///
-    /// # Errors
-    ///
-    /// - [`InvalidString`][] if the provided password contains a null byte
-    /// - [`WrongPassword`][] if the admin password is wrong
-    ///
-    /// # Example
-    ///
-    /// ```no_run
-    /// use nitrokey::Device;
-    /// # use nitrokey::CommandError;
-    ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
-    /// match device.factory_reset("12345678") {
-    ///     Ok(()) => println!("Performed a factory reset."),
-    ///     Err(err) => println!("Could not perform a factory reset: {}", err),
-    /// };
-    /// #     Ok(())
-    /// # }
-    /// ```
-    ///
-    /// [`build_aes_key`]: #method.build_aes_key
-    fn factory_reset(&self, admin_pin: &str) -> Result<(), CommandError> {
-        let admin_pin_string = get_cstring(admin_pin)?;
-        unsafe { get_command_result(nitrokey_sys::NK_factory_reset(admin_pin_string.as_ptr())) }
-    }
-
-    /// Builds a new AES key on the Nitrokey.
-    ///
-    /// The AES key is used to encrypt the password safe and the encrypted volume.  You may need
-    /// to call this method after a factory reset, either using [`factory_reset`][] or using `gpg
-    /// --card-edit`.  You can also use it to destroy the data stored in the password safe or on
-    /// the encrypted volume.
-    ///
-    /// # Errors
-    ///
-    /// - [`InvalidString`][] if the provided password contains a null byte
-    /// - [`WrongPassword`][] if the admin password is wrong
-    ///
-    /// # Example
-    ///
-    /// ```no_run
-    /// use nitrokey::Device;
-    /// # use nitrokey::CommandError;
-    ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
-    /// match device.build_aes_key("12345678") {
-    ///     Ok(()) => println!("New AES keys have been built."),
-    ///     Err(err) => println!("Could not build new AES keys: {}", err),
-    /// };
-    /// #     Ok(())
-    /// # }
-    /// ```
-    ///
-    /// [`factory_reset`]: #method.factory_reset
-    fn build_aes_key(&self, admin_pin: &str) -> Result<(), CommandError> {
-        let admin_pin_string = get_cstring(admin_pin)?;
-        unsafe { get_command_result(nitrokey_sys::NK_build_aes_key(admin_pin_string.as_ptr())) }
-    }
-}
-
-/// Connects to a Nitrokey device.  This method can be used to connect to any connected device,
-/// both a Nitrokey Pro and a Nitrokey Storage.
-///
-/// # Errors
-///
-/// - [`Undefined`][] if no Nitrokey device is connected
-///
-/// # Example
-///
-/// ```
-/// use nitrokey::DeviceWrapper;
-///
-/// fn do_something(device: DeviceWrapper) {}
-///
-/// match nitrokey::connect() {
-///     Ok(device) => do_something(device),
-///     Err(err) => println!("Could not connect to a Nitrokey: {}", err),
-/// }
-/// ```
-///
-/// [`Undefined`]: enum.CommandError.html#variant.Undefined
-pub fn connect() -> Result<DeviceWrapper, CommandError> {
-    unsafe {
-        match nitrokey_sys::NK_login_auto() {
-            1 => match get_connected_device() {
-                Some(wrapper) => Ok(wrapper),
-                None => Err(CommandError::Undefined),
-            },
-            _ => Err(CommandError::Undefined),
-        }
-    }
-}
-
-/// Connects to a Nitrokey device of the given model.
-///
-/// # Errors
-///
-/// - [`Undefined`][] if no Nitrokey device of the given model is connected
-///
-/// # Example
-///
-/// ```
-/// use nitrokey::DeviceWrapper;
-/// use nitrokey::Model;
-///
-/// fn do_something(device: DeviceWrapper) {}
-///
-/// match nitrokey::connect_model(Model::Pro) {
-///     Ok(device) => do_something(device),
-///     Err(err) => println!("Could not connect to a Nitrokey Pro: {}", err),
-/// }
-/// ```
-///
-/// [`Undefined`]: enum.CommandError.html#variant.Undefined
-pub fn connect_model(model: Model) -> Result<DeviceWrapper, CommandError> {
-    if connect_enum(model) {
-        Ok(create_device_wrapper(model))
-    } else {
-        Err(CommandError::Undefined)
-    }
-}
-
-fn get_connected_model() -> Option<Model> {
-    unsafe {
-        match nitrokey_sys::NK_get_device_model() {
-            nitrokey_sys::NK_device_model_NK_PRO => Some(Model::Pro),
-            nitrokey_sys::NK_device_model_NK_STORAGE => Some(Model::Storage),
-            _ => None,
-        }
-    }
-}
-
-fn create_device_wrapper(model: Model) -> DeviceWrapper {
-    match model {
-        Model::Pro => DeviceWrapper::Pro(Pro {}),
-        Model::Storage => DeviceWrapper::Storage(Storage {}),
-    }
-}
-
-fn get_connected_device() -> Option<DeviceWrapper> {
-    get_connected_model().map(create_device_wrapper)
-}
-
-fn connect_enum(model: Model) -> bool {
-    let model = match model {
-        Model::Storage => nitrokey_sys::NK_device_model_NK_STORAGE,
-        Model::Pro => nitrokey_sys::NK_device_model_NK_PRO,
-    };
-    unsafe { nitrokey_sys::NK_login_enum(model) == 1 }
-}
-
-impl DeviceWrapper {
-    fn device(&self) -> &dyn Device {
-        match *self {
-            DeviceWrapper::Storage(ref storage) => storage,
-            DeviceWrapper::Pro(ref pro) => pro,
-        }
-    }
-}
-
-impl GenerateOtp for DeviceWrapper {
-    fn get_hotp_slot_name(&self, slot: u8) -> Result<String, CommandError> {
-        self.device().get_hotp_slot_name(slot)
-    }
-
-    fn get_totp_slot_name(&self, slot: u8) -> Result<String, CommandError> {
-        self.device().get_totp_slot_name(slot)
-    }
-
-    fn get_hotp_code(&self, slot: u8) -> Result<String, CommandError> {
-        self.device().get_hotp_code(slot)
-    }
-
-    fn get_totp_code(&self, slot: u8) -> Result<String, CommandError> {
-        self.device().get_totp_code(slot)
-    }
-}
-
-impl Device for DeviceWrapper {
-    fn get_model(&self) -> Model {
-        match *self {
-            DeviceWrapper::Pro(_) => Model::Pro,
-            DeviceWrapper::Storage(_) => Model::Storage,
-        }
-    }
-}
-
-impl Pro {
-    /// Connects to a Nitrokey Pro.
-    ///
-    /// # Errors
-    ///
-    /// - [`Undefined`][] if no Nitrokey device of the given model is connected
-    ///
-    /// # Example
-    ///
-    /// ```
-    /// use nitrokey::Pro;
-    ///
-    /// fn use_pro(device: Pro) {}
-    ///
-    /// match nitrokey::Pro::connect() {
-    ///     Ok(device) => use_pro(device),
-    ///     Err(err) => println!("Could not connect to the Nitrokey Pro: {}", err),
-    /// }
-    /// ```
-    ///
-    /// [`Undefined`]: enum.CommandError.html#variant.Undefined
-    pub fn connect() -> Result<Pro, CommandError> {
-        // TODO: maybe Option instead of Result?
-        match connect_enum(Model::Pro) {
-            true => Ok(Pro {}),
-            false => Err(CommandError::Undefined),
-        }
-    }
-}
-
-impl Drop for Pro {
-    fn drop(&mut self) {
-        unsafe {
-            nitrokey_sys::NK_logout();
-        }
-    }
-}
-
-impl Device for Pro {
-    fn get_model(&self) -> Model {
-        Model::Pro
-    }
-}
-
-impl GenerateOtp for Pro {}
-
-impl Storage {
-    /// Connects to a Nitrokey Storage.
-    ///
-    /// # Errors
-    ///
-    /// - [`Undefined`][] if no Nitrokey device of the given model is connected
-    ///
-    /// # Example
-    ///
-    /// ```
-    /// use nitrokey::Storage;
-    ///
-    /// fn use_storage(device: Storage) {}
-    ///
-    /// match nitrokey::Storage::connect() {
-    ///     Ok(device) => use_storage(device),
-    ///     Err(err) => println!("Could not connect to the Nitrokey Storage: {}", err),
-    /// }
-    /// ```
-    ///
-    /// [`Undefined`]: enum.CommandError.html#variant.Undefined
-    pub fn connect() -> Result<Storage, CommandError> {
-        // TODO: maybe Option instead of Result?
-        match connect_enum(Model::Storage) {
-            true => Ok(Storage {}),
-            false => Err(CommandError::Undefined),
-        }
-    }
-
-    /// Changes the update PIN.
-    ///
-    /// The update PIN is used to enable firmware updates.  Unlike the user and the admin PIN, the
-    /// update PIN is not managed by the OpenPGP smart card but by the Nitrokey firmware.  There is
-    /// no retry counter as with the other PIN types.
-    ///
-    /// # Errors
-    ///
-    /// - [`InvalidString`][] if one of the provided passwords contains a null byte
-    /// - [`WrongPassword`][] if the current update password is wrong
-    ///
-    /// # Example
-    ///
-    /// ```no_run
-    /// # use nitrokey::CommandError;
-    ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::Storage::connect()?;
-    /// match device.change_update_pin("12345678", "87654321") {
-    ///     Ok(()) => println!("Updated update PIN."),
-    ///     Err(err) => println!("Failed to update update PIN: {}", err),
-    /// };
-    /// #     Ok(())
-    /// # }
-    /// ```
-    ///
-    /// [`InvalidString`]: enum.CommandError.html#variant.InvalidString
-    /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    pub fn change_update_pin(&self, current: &str, new: &str) -> Result<(), CommandError> {
-        let current_string = get_cstring(current)?;
-        let new_string = get_cstring(new)?;
-        unsafe {
-            get_command_result(nitrokey_sys::NK_change_update_password(
-                current_string.as_ptr(),
-                new_string.as_ptr(),
-            ))
-        }
-    }
-
-    /// Enables the firmware update mode.
-    ///
-    /// During firmware update mode, the Nitrokey can no longer be accessed using HID commands.
-    /// To resume normal operation, run `dfu-programmer at32uc3a3256s launch`.  In order to enter
-    /// the firmware update mode, you need the update password that can be changed using the
-    /// [`change_update_pin`][] method.
-    ///
-    /// # Errors
-    ///
-    /// - [`InvalidString`][] if one of the provided passwords contains a null byte
-    /// - [`WrongPassword`][] if the current update password is wrong
-    ///
-    /// # Example
-    ///
-    /// ```no_run
-    /// # use nitrokey::CommandError;
-    ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::Storage::connect()?;
-    /// match device.enable_firmware_update("12345678") {
-    ///     Ok(()) => println!("Nitrokey entered update mode."),
-    ///     Err(err) => println!("Could not enter update mode: {}", err),
-    /// };
-    /// #     Ok(())
-    /// # }
-    /// ```
-    ///
-    /// [`InvalidString`]: enum.CommandError.html#variant.InvalidString
-    /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    pub fn enable_firmware_update(&self, update_pin: &str) -> Result<(), CommandError> {
-        let update_pin_string = get_cstring(update_pin)?;
-        unsafe {
-            get_command_result(nitrokey_sys::NK_enable_firmware_update(
-                update_pin_string.as_ptr(),
-            ))
-        }
-    }
-
-    /// Enables the encrypted storage volume.
-    ///
-    /// Once the encrypted volume is enabled, it is presented to the operating system as a block
-    /// device.  The API does not provide any information on the name or path of this block device.
-    ///
-    /// # Errors
-    ///
-    /// - [`InvalidString`][] if the provided password contains a null byte
-    /// - [`WrongPassword`][] if the provided user password is wrong
-    ///
-    /// # Example
-    ///
-    /// ```no_run
-    /// # use nitrokey::CommandError;
-    ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::Storage::connect()?;
-    /// match device.enable_encrypted_volume("123456") {
-    ///     Ok(()) => println!("Enabled the encrypted volume."),
-    ///     Err(err) => println!("Could not enable the encrypted volume: {}", err),
-    /// };
-    /// #     Ok(())
-    /// # }
-    /// ```
-    ///
-    /// [`InvalidString`]: enum.CommandError.html#variant.InvalidString
-    /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    pub fn enable_encrypted_volume(&self, user_pin: &str) -> Result<(), CommandError> {
-        let user_pin = get_cstring(user_pin)?;
-        unsafe { get_command_result(nitrokey_sys::NK_unlock_encrypted_volume(user_pin.as_ptr())) }
-    }
-
-    /// Disables the encrypted storage volume.
-    ///
-    /// Once the volume is disabled, it can be no longer accessed as a block device.  If the
-    /// encrypted volume has not been enabled, this method still returns a success.
-    ///
-    /// # Example
-    ///
-    /// ```no_run
-    /// # use nitrokey::CommandError;
-    ///
-    /// fn use_volume() {}
-    ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::Storage::connect()?;
-    /// match device.enable_encrypted_volume("123456") {
-    ///     Ok(()) => {
-    ///         println!("Enabled the encrypted volume.");
-    ///         use_volume();
-    ///         match device.disable_encrypted_volume() {
-    ///             Ok(()) => println!("Disabled the encrypted volume."),
-    ///             Err(err) => {
-    ///                 println!("Could not disable the encrypted volume: {}", err);
-    ///             },
-    ///         };
-    ///     },
-    ///     Err(err) => println!("Could not enable the encrypted volume: {}", err),
-    /// };
-    /// #     Ok(())
-    /// # }
-    /// ```
-    pub fn disable_encrypted_volume(&self) -> Result<(), CommandError> {
-        unsafe { get_command_result(nitrokey_sys::NK_lock_encrypted_volume()) }
-    }
-
-    /// Enables a hidden storage volume.
-    ///
-    /// This function will only succeed if the encrypted storage ([`enable_encrypted_volume`][]) or
-    /// another hidden volume has been enabled previously.  Once the hidden volume is enabled, it
-    /// is presented to the operating system as a block device and any previously opened encrypted
-    /// or hidden volumes are closed.  The API does not provide any information on the name or path
-    /// of this block device.
-    ///
-    /// Note that the encrypted and the hidden volumes operate on the same storage area, so using
-    /// both at the same time might lead to data loss.
-    ///
-    /// The hidden volume to unlock is selected based on the provided password.
-    ///
-    /// # Errors
-    ///
-    /// - [`AesDecryptionFailed`][] if the encrypted storage has not been opened before calling
-    ///   this method or the AES key has not been built
-    /// - [`InvalidString`][] if the provided password contains a null byte
-    ///
-    /// # Example
-    ///
-    /// ```no_run
-    /// # use nitrokey::CommandError;
-    ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::Storage::connect()?;
-    /// device.enable_encrypted_volume("123445")?;
-    /// match device.enable_hidden_volume("hidden-pw") {
-    ///     Ok(()) => println!("Enabled a hidden volume."),
-    ///     Err(err) => println!("Could not enable the hidden volume: {}", err),
-    /// };
-    /// #     Ok(())
-    /// # }
-    /// ```
-    ///
-    /// [`enable_encrypted_volume`]: #method.enable_encrypted_volume
-    /// [`AesDecryptionFailed`]: enum.CommandError.html#variant.AesDecryptionFailed
-    /// [`InvalidString`]: enum.CommandError.html#variant.InvalidString
-    pub fn enable_hidden_volume(&self, volume_password: &str) -> Result<(), CommandError> {
-        let volume_password = get_cstring(volume_password)?;
-        unsafe {
-            get_command_result(nitrokey_sys::NK_unlock_hidden_volume(
-                volume_password.as_ptr(),
-            ))
-        }
-    }
-
-    /// Disables a hidden storage volume.
-    ///
-    /// Once the volume is disabled, it can be no longer accessed as a block device.  If no hidden
-    /// volume has been enabled, this method still returns a success.
-    ///
-    /// # Example
-    ///
-    /// ```no_run
-    /// # use nitrokey::CommandError;
-    ///
-    /// fn use_volume() {}
-    ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::Storage::connect()?;
-    /// device.enable_encrypted_volume("123445")?;
-    /// match device.enable_hidden_volume("hidden-pw") {
-    ///     Ok(()) => {
-    ///         println!("Enabled the hidden volume.");
-    ///         use_volume();
-    ///         match device.disable_hidden_volume() {
-    ///             Ok(()) => println!("Disabled the hidden volume."),
-    ///             Err(err) => {
-    ///                 println!("Could not disable the hidden volume: {}", err);
-    ///             },
-    ///         };
-    ///     },
-    ///     Err(err) => println!("Could not enable the hidden volume: {}", err),
-    /// };
-    /// #     Ok(())
-    /// # }
-    /// ```
-    pub fn disable_hidden_volume(&self) -> Result<(), CommandError> {
-        unsafe { get_command_result(nitrokey_sys::NK_lock_hidden_volume()) }
-    }
-
-    /// Creates a hidden volume.
-    ///
-    /// The volume is crated in the given slot and in the given range of the available memory,
-    /// where `start` is the start position as a percentage of the available memory, and `end` is
-    /// the end position as a percentage of the available memory.  The volume will be protected by
-    /// the given password.
-    ///
-    /// Note that the encrypted and the hidden volumes operate on the same storage area, so using
-    /// both at the same time might lead to data loss.
-    ///
-    /// According to the libnitrokey documentation, this function only works if the encrypted
-    /// storage has been opened.
-    ///
-    /// # Errors
-    ///
-    /// - [`AesDecryptionFailed`][] if the encrypted storage has not been opened before calling
-    ///   this method or the AES key has not been built
-    /// - [`InvalidString`][] if the provided password contains a null byte
-    ///
-    /// # Example
-    ///
-    /// ```no_run
-    /// # use nitrokey::CommandError;
-    ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::Storage::connect()?;
-    /// device.enable_encrypted_volume("123445")?;
-    /// device.create_hidden_volume(0, 0, 100, "hidden-pw")?;
-    /// #     Ok(())
-    /// # }
-    /// ```
-    ///
-    /// [`AesDecryptionFailed`]: enum.CommandError.html#variant.AesDecryptionFailed
-    /// [`InvalidString`]: enum.CommandError.html#variant.InvalidString
-    pub fn create_hidden_volume(
-        &self,
-        slot: u8,
-        start: u8,
-        end: u8,
-        password: &str,
-    ) -> Result<(), CommandError> {
-        let password = get_cstring(password)?;
-        unsafe {
-            get_command_result(nitrokey_sys::NK_create_hidden_volume(
-                slot,
-                start,
-                end,
-                password.as_ptr(),
-            ))
-        }
-    }
-
-    /// Sets the access mode of the unencrypted volume.
-    ///
-    /// This command will reconnect the unencrypted volume so buffers should be flushed before
-    /// calling it.  Since firmware version v0.51, this command requires the admin PIN.  Older
-    /// firmware versions are not supported.
-    ///
-    /// # Errors
-    ///
-    /// - [`InvalidString`][] if the provided password contains a null byte
-    /// - [`WrongPassword`][] if the provided admin password is wrong
-    ///
-    /// # Example
-    ///
-    /// ```no_run
-    /// # use nitrokey::CommandError;
-    /// use nitrokey::VolumeMode;
-    ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::Storage::connect()?;
-    /// match device.set_unencrypted_volume_mode("123456", VolumeMode::ReadWrite) {
-    ///     Ok(()) => println!("Set the unencrypted volume to read-write mode."),
-    ///     Err(err) => println!("Could not set the unencrypted volume to read-write mode: {}", err),
-    /// };
-    /// #     Ok(())
-    /// # }
-    /// ```
-    ///
-    /// [`InvalidString`]: enum.CommandError.html#variant.InvalidString
-    /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    pub fn set_unencrypted_volume_mode(
-        &self,
-        admin_pin: &str,
-        mode: VolumeMode,
-    ) -> Result<(), CommandError> {
-        let admin_pin = get_cstring(admin_pin)?;
-        let result = match mode {
-            VolumeMode::ReadOnly => unsafe {
-                nitrokey_sys::NK_set_unencrypted_read_only_admin(admin_pin.as_ptr())
-            },
-            VolumeMode::ReadWrite => unsafe {
-                nitrokey_sys::NK_set_unencrypted_read_write_admin(admin_pin.as_ptr())
-            },
-        };
-        get_command_result(result)
-    }
-
-    /// Returns the status of the connected storage device.
-    ///
-    /// # Example
-    ///
-    /// ```no_run
-    /// # use nitrokey::CommandError;
-    ///
-    /// fn use_volume() {}
-    ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::Storage::connect()?;
-    /// match device.get_status() {
-    ///     Ok(status) => {
-    ///         println!("SD card ID: {:#x}", status.serial_number_sd_card);
-    ///     },
-    ///     Err(err) => println!("Could not get Storage status: {}", err),
-    /// };
-    /// #     Ok(())
-    /// # }
-    /// ```
-    pub fn get_status(&self) -> Result<StorageStatus, CommandError> {
-        let mut raw_status = nitrokey_sys::NK_storage_status {
-            unencrypted_volume_read_only: false,
-            unencrypted_volume_active: false,
-            encrypted_volume_read_only: false,
-            encrypted_volume_active: false,
-            hidden_volume_read_only: false,
-            hidden_volume_active: false,
-            firmware_version_major: 0,
-            firmware_version_minor: 0,
-            firmware_locked: false,
-            serial_number_sd_card: 0,
-            serial_number_smart_card: 0,
-            user_retry_count: 0,
-            admin_retry_count: 0,
-            new_sd_card_found: false,
-            filled_with_random: false,
-            stick_initialized: false,
-        };
-        let raw_result = unsafe { nitrokey_sys::NK_get_status_storage(&mut raw_status) };
-        let result = get_command_result(raw_result);
-        result.and(Ok(StorageStatus::from(raw_status)))
-    }
-
-    /// Returns the production information for the connected storage device.
-    ///
-    /// # Example
-    ///
-    /// ```no_run
-    /// # use nitrokey::CommandError;
-    ///
-    /// fn use_volume() {}
-    ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::Storage::connect()?;
-    /// match device.get_production_info() {
-    ///     Ok(data) => {
-    ///         println!("SD card ID:   {:#x}", data.sd_card.serial_number);
-    ///         println!("SD card size: {} GB", data.sd_card.size);
-    ///     },
-    ///     Err(err) => println!("Could not get Storage production info: {}", err),
-    /// };
-    /// #     Ok(())
-    /// # }
-    /// ```
-    pub fn get_production_info(&self) -> Result<StorageProductionInfo, CommandError> {
-        let mut raw_data = nitrokey_sys::NK_storage_ProductionTest {
-            FirmwareVersion_au8: [0, 2],
-            FirmwareVersionInternal_u8: 0,
-            SD_Card_Size_u8: 0,
-            CPU_CardID_u32: 0,
-            SmartCardID_u32: 0,
-            SD_CardID_u32: 0,
-            SC_UserPwRetryCount: 0,
-            SC_AdminPwRetryCount: 0,
-            SD_Card_ManufacturingYear_u8: 0,
-            SD_Card_ManufacturingMonth_u8: 0,
-            SD_Card_OEM_u16: 0,
-            SD_WriteSpeed_u16: 0,
-            SD_Card_Manufacturer_u8: 0,
-        };
-        let raw_result = unsafe { nitrokey_sys::NK_get_storage_production_info(&mut raw_data) };
-        let result = get_command_result(raw_result);
-        result.and(Ok(StorageProductionInfo::from(raw_data)))
-    }
-
-    /// Clears the warning for a new SD card.
-    ///
-    /// The Storage status contains a field for a new SD card warning.  After a factory reset, the
-    /// field is set to true.  After filling the SD card with random data, it is set to false.
-    /// This method can be used to set it to false without filling the SD card with random data.
-    ///
-    /// # Errors
-    ///
-    /// - [`InvalidString`][] if the provided password contains a null byte
-    /// - [`WrongPassword`][] if the provided admin password is wrong
-    ///
-    /// # Example
-    ///
-    /// ```no_run
-    /// # use nitrokey::CommandError;
-    ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::Storage::connect()?;
-    /// match device.clear_new_sd_card_warning("12345678") {
-    ///     Ok(()) => println!("Cleared the new SD card warning."),
-    ///     Err(err) => println!("Could not set the clear the new SD card warning: {}", err),
-    /// };
-    /// #     Ok(())
-    /// # }
-    /// ```
-    ///
-    /// [`InvalidString`]: enum.CommandError.html#variant.InvalidString
-    /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    pub fn clear_new_sd_card_warning(&self, admin_pin: &str) -> Result<(), CommandError> {
-        let admin_pin = get_cstring(admin_pin)?;
-        get_command_result(unsafe {
-            nitrokey_sys::NK_clear_new_sd_card_warning(admin_pin.as_ptr())
-        })
-    }
-
-    /// Blinks the red and green LED alternatively and infinitely until the device is reconnected.
-    pub fn wink(&self) -> Result<(), CommandError> {
-        get_command_result(unsafe { nitrokey_sys::NK_wink() })
-    }
-
-    /// Exports the firmware to the unencrypted volume.
-    ///
-    /// This command requires the admin PIN.  The unencrypted volume must be in read-write mode
-    /// when this command is executed.  Otherwise, it will still return `Ok` but not write the
-    /// firmware.
-    ///
-    /// This command unmounts the unencrypted volume if it has been mounted, so all buffers should
-    /// be flushed.  The firmware is written to the `firmware.bin` file on the unencrypted volume.
-    ///
-    /// # Errors
-    ///
-    /// - [`InvalidString`][] if one of the provided passwords contains a null byte
-    /// - [`WrongPassword`][] if the admin password is wrong
-    ///
-    /// [`InvalidString`]: enum.CommandError.html#variant.InvalidString
-    /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    pub fn export_firmware(&self, admin_pin: &str) -> Result<(), CommandError> {
-        let admin_pin_string = get_cstring(admin_pin)?;
-        get_command_result(unsafe { nitrokey_sys::NK_export_firmware(admin_pin_string.as_ptr()) })
-    }
-}
-
-impl Drop for Storage {
-    fn drop(&mut self) {
-        unsafe {
-            nitrokey_sys::NK_logout();
-        }
-    }
-}
-
-impl Device for Storage {
-    fn get_model(&self) -> Model {
-        Model::Storage
-    }
-}
-
-impl GenerateOtp for Storage {}
-
-impl From<nitrokey_sys::NK_storage_ProductionTest> for StorageProductionInfo {
-    fn from(data: nitrokey_sys::NK_storage_ProductionTest) -> Self {
-        Self {
-            firmware_version_major: data.FirmwareVersion_au8[0],
-            firmware_version_minor: data.FirmwareVersion_au8[1],
-            firmware_version_internal: data.FirmwareVersionInternal_u8,
-            serial_number_cpu: data.CPU_CardID_u32,
-            sd_card: SdCardData {
-                serial_number: data.SD_CardID_u32,
-                size: data.SD_Card_Size_u8,
-                manufacturing_year: data.SD_Card_ManufacturingYear_u8,
-                manufacturing_month: data.SD_Card_ManufacturingMonth_u8,
-                oem: data.SD_Card_OEM_u16,
-                manufacturer: data.SD_Card_Manufacturer_u8,
-            },
-        }
-    }
-}
-
-impl From<nitrokey_sys::NK_storage_status> for StorageStatus {
-    fn from(status: nitrokey_sys::NK_storage_status) -> Self {
-        StorageStatus {
-            unencrypted_volume: VolumeStatus {
-                read_only: status.unencrypted_volume_read_only,
-                active: status.unencrypted_volume_active,
-            },
-            encrypted_volume: VolumeStatus {
-                read_only: status.encrypted_volume_read_only,
-                active: status.encrypted_volume_active,
-            },
-            hidden_volume: VolumeStatus {
-                read_only: status.hidden_volume_read_only,
-                active: status.hidden_volume_active,
-            },
-            firmware_version_major: status.firmware_version_major,
-            firmware_version_minor: status.firmware_version_minor,
-            firmware_locked: status.firmware_locked,
-            serial_number_sd_card: status.serial_number_sd_card,
-            serial_number_smart_card: status.serial_number_smart_card,
-            user_retry_count: status.user_retry_count,
-            admin_retry_count: status.admin_retry_count,
-            new_sd_card_found: status.new_sd_card_found,
-            filled_with_random: status.filled_with_random,
-            stick_initialized: status.stick_initialized,
-        }
-    }
-}
diff --git a/src/device/mod.rs b/src/device/mod.rs
new file mode 100644
index 0000000..5e15f08
--- /dev/null
+++ b/src/device/mod.rs
@@ -0,0 +1,464 @@
+// Copyright (C) 2018-2019 Robin Krahl <robin.krahl@ireas.org>
+// SPDX-License-Identifier: MIT
+
+mod pro;
+mod storage;
+mod wrapper;
+
+use std::fmt;
+
+use libc;
+use nitrokey_sys;
+
+use crate::auth::Authenticate;
+use crate::config::{Config, RawConfig};
+use crate::error::{CommunicationError, Error};
+use crate::otp::GenerateOtp;
+use crate::pws::GetPasswordSafe;
+use crate::util::{
+    get_command_result, get_cstring, get_last_error, result_from_string, result_or_error,
+};
+
+pub use pro::Pro;
+pub use storage::{
+    SdCardData, Storage, StorageProductionInfo, StorageStatus, VolumeMode, VolumeStatus,
+};
+pub use wrapper::DeviceWrapper;
+
+/// Available Nitrokey models.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum Model {
+    /// The Nitrokey Storage.
+    Storage,
+    /// The Nitrokey Pro.
+    Pro,
+}
+
+impl fmt::Display for Model {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(match *self {
+            Model::Pro => "Pro",
+            Model::Storage => "Storage",
+        })
+    }
+}
+
+/// A firmware version for a Nitrokey device.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct FirmwareVersion {
+    /// The major firmware version, e. g. 0 in v0.40.
+    pub major: u8,
+    /// The minor firmware version, e. g. 40 in v0.40.
+    pub minor: u8,
+}
+
+impl fmt::Display for FirmwareVersion {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "v{}.{}", self.major, self.minor)
+    }
+}
+
+/// A Nitrokey device.
+///
+/// This trait provides the commands that can be executed without authentication and that are
+/// present on all supported Nitrokey devices.
+pub trait Device<'a>: Authenticate<'a> + GetPasswordSafe<'a> + GenerateOtp + fmt::Debug {
+    /// Returns the [`Manager`][] instance that has been used to connect to this device.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use nitrokey::{Device, DeviceWrapper};
+    ///
+    /// fn do_something(device: DeviceWrapper) {
+    ///     // reconnect to any device
+    ///     let manager = device.into_manager();
+    ///     let device = manager.connect();
+    ///     // do something with the device
+    ///     // ...
+    /// }
+    ///
+    /// match nitrokey::take()?.connect() {
+    ///     Ok(device) => do_something(device),
+    ///     Err(err) => println!("Could not connect to a Nitrokey: {}", err),
+    /// }
+    /// # Ok::<(), nitrokey::Error>(())
+    /// ```
+    fn into_manager(self) -> &'a mut crate::Manager;
+
+    /// Returns the model of the connected Nitrokey device.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// use nitrokey::Device;
+    /// # use nitrokey::Error;
+    ///
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let device = manager.connect()?;
+    /// println!("Connected to a Nitrokey {}", device.get_model());
+    /// #    Ok(())
+    /// # }
+    fn get_model(&self) -> Model;
+
+    /// Returns the serial number of the Nitrokey device.  The serial number is the string
+    /// representation of a hex number.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// use nitrokey::Device;
+    /// # use nitrokey::Error;
+    ///
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let device = manager.connect()?;
+    /// match device.get_serial_number() {
+    ///     Ok(number) => println!("serial no: {}", number),
+    ///     Err(err) => eprintln!("Could not get serial number: {}", err),
+    /// };
+    /// #     Ok(())
+    /// # }
+    /// ```
+    fn get_serial_number(&self) -> Result<String, Error> {
+        result_from_string(unsafe { nitrokey_sys::NK_device_serial_number() })
+    }
+
+    /// Returns the number of remaining authentication attempts for the user.  The total number of
+    /// available attempts is three.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// use nitrokey::Device;
+    /// # use nitrokey::Error;
+    ///
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let device = manager.connect()?;
+    /// let count = device.get_user_retry_count();
+    /// match device.get_user_retry_count() {
+    ///     Ok(count) => println!("{} remaining authentication attempts (user)", count),
+    ///     Err(err) => eprintln!("Could not get user retry count: {}", err),
+    /// }
+    /// #     Ok(())
+    /// # }
+    /// ```
+    fn get_user_retry_count(&self) -> Result<u8, Error> {
+        result_or_error(unsafe { nitrokey_sys::NK_get_user_retry_count() })
+    }
+
+    /// Returns the number of remaining authentication attempts for the admin.  The total number of
+    /// available attempts is three.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// use nitrokey::Device;
+    /// # use nitrokey::Error;
+    ///
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let device = manager.connect()?;
+    /// let count = device.get_admin_retry_count();
+    /// match device.get_admin_retry_count() {
+    ///     Ok(count) => println!("{} remaining authentication attempts (admin)", count),
+    ///     Err(err) => eprintln!("Could not get admin retry count: {}", err),
+    /// }
+    /// #     Ok(())
+    /// # }
+    /// ```
+    fn get_admin_retry_count(&self) -> Result<u8, Error> {
+        result_or_error(unsafe { nitrokey_sys::NK_get_admin_retry_count() })
+    }
+
+    /// Returns the firmware version.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// use nitrokey::Device;
+    /// # use nitrokey::Error;
+    ///
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let device = manager.connect()?;
+    /// match device.get_firmware_version() {
+    ///     Ok(version) => println!("Firmware version: {}", version),
+    ///     Err(err) => eprintln!("Could not access firmware version: {}", err),
+    /// };
+    /// #     Ok(())
+    /// # }
+    /// ```
+    fn get_firmware_version(&self) -> Result<FirmwareVersion, Error> {
+        let major = result_or_error(unsafe { nitrokey_sys::NK_get_major_firmware_version() })?;
+        let minor = result_or_error(unsafe { nitrokey_sys::NK_get_minor_firmware_version() })?;
+        Ok(FirmwareVersion { major, minor })
+    }
+
+    /// Returns the current configuration of the Nitrokey device.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// use nitrokey::Device;
+    /// # use nitrokey::Error;
+    ///
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let device = manager.connect()?;
+    /// let config = device.get_config()?;
+    /// println!("numlock binding:          {:?}", config.numlock);
+    /// println!("capslock binding:         {:?}", config.capslock);
+    /// println!("scrollock binding:        {:?}", config.scrollock);
+    /// println!("require password for OTP: {:?}", config.user_password);
+    /// #     Ok(())
+    /// # }
+    /// ```
+    fn get_config(&self) -> Result<Config, Error> {
+        let config_ptr = unsafe { nitrokey_sys::NK_read_config() };
+        if config_ptr.is_null() {
+            return Err(get_last_error());
+        }
+        let config_array_ptr = config_ptr as *const [u8; 5];
+        let raw_config = unsafe { RawConfig::from(*config_array_ptr) };
+        unsafe { libc::free(config_ptr as *mut libc::c_void) };
+        Ok(raw_config.into())
+    }
+
+    /// Changes the administrator PIN.
+    ///
+    /// # Errors
+    ///
+    /// - [`InvalidString`][] if one of the provided passwords contains a null byte
+    /// - [`WrongPassword`][] if the current admin password is wrong
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// use nitrokey::Device;
+    /// # use nitrokey::Error;
+    ///
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let mut device = manager.connect()?;
+    /// match device.change_admin_pin("12345678", "12345679") {
+    ///     Ok(()) => println!("Updated admin PIN."),
+    ///     Err(err) => eprintln!("Failed to update admin PIN: {}", err),
+    /// };
+    /// #     Ok(())
+    /// # }
+    /// ```
+    ///
+    /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
+    /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
+    fn change_admin_pin(&mut self, current: &str, new: &str) -> Result<(), Error> {
+        let current_string = get_cstring(current)?;
+        let new_string = get_cstring(new)?;
+        get_command_result(unsafe {
+            nitrokey_sys::NK_change_admin_PIN(current_string.as_ptr(), new_string.as_ptr())
+        })
+    }
+
+    /// Changes the user PIN.
+    ///
+    /// # Errors
+    ///
+    /// - [`InvalidString`][] if one of the provided passwords contains a null byte
+    /// - [`WrongPassword`][] if the current user password is wrong
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// use nitrokey::Device;
+    /// # use nitrokey::Error;
+    ///
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let mut device = manager.connect()?;
+    /// match device.change_user_pin("123456", "123457") {
+    ///     Ok(()) => println!("Updated admin PIN."),
+    ///     Err(err) => eprintln!("Failed to update admin PIN: {}", err),
+    /// };
+    /// #     Ok(())
+    /// # }
+    /// ```
+    ///
+    /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
+    /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
+    fn change_user_pin(&mut self, current: &str, new: &str) -> Result<(), Error> {
+        let current_string = get_cstring(current)?;
+        let new_string = get_cstring(new)?;
+        get_command_result(unsafe {
+            nitrokey_sys::NK_change_user_PIN(current_string.as_ptr(), new_string.as_ptr())
+        })
+    }
+
+    /// Unlocks the user PIN after three failed login attempts and sets it to the given value.
+    ///
+    /// # Errors
+    ///
+    /// - [`InvalidString`][] if one of the provided passwords contains a null byte
+    /// - [`WrongPassword`][] if the admin password is wrong
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// use nitrokey::Device;
+    /// # use nitrokey::Error;
+    ///
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let mut device = manager.connect()?;
+    /// match device.unlock_user_pin("12345678", "123456") {
+    ///     Ok(()) => println!("Unlocked user PIN."),
+    ///     Err(err) => eprintln!("Failed to unlock user PIN: {}", err),
+    /// };
+    /// #     Ok(())
+    /// # }
+    /// ```
+    ///
+    /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
+    /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
+    fn unlock_user_pin(&mut self, admin_pin: &str, user_pin: &str) -> Result<(), Error> {
+        let admin_pin_string = get_cstring(admin_pin)?;
+        let user_pin_string = get_cstring(user_pin)?;
+        get_command_result(unsafe {
+            nitrokey_sys::NK_unlock_user_password(
+                admin_pin_string.as_ptr(),
+                user_pin_string.as_ptr(),
+            )
+        })
+    }
+
+    /// Locks the Nitrokey device.
+    ///
+    /// This disables the password store if it has been unlocked.  On the Nitrokey Storage, this
+    /// also disables the volumes if they have been enabled.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// use nitrokey::Device;
+    /// # use nitrokey::Error;
+    ///
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let mut device = manager.connect()?;
+    /// match device.lock() {
+    ///     Ok(()) => println!("Locked the Nitrokey device."),
+    ///     Err(err) => eprintln!("Could not lock the Nitrokey device: {}", err),
+    /// };
+    /// #     Ok(())
+    /// # }
+    /// ```
+    fn lock(&mut self) -> Result<(), Error> {
+        get_command_result(unsafe { nitrokey_sys::NK_lock_device() })
+    }
+
+    /// Performs a factory reset on the Nitrokey device.
+    ///
+    /// This commands performs a factory reset on the smart card (like the factory reset via `gpg
+    /// --card-edit`) and then clears the flash memory (password safe, one-time passwords etc.).
+    /// After a factory reset, [`build_aes_key`][] has to be called before the password safe or the
+    /// encrypted volume can be used.
+    ///
+    /// # Errors
+    ///
+    /// - [`InvalidString`][] if the provided password contains a null byte
+    /// - [`WrongPassword`][] if the admin password is wrong
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// use nitrokey::Device;
+    /// # use nitrokey::Error;
+    ///
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let mut device = manager.connect()?;
+    /// match device.factory_reset("12345678") {
+    ///     Ok(()) => println!("Performed a factory reset."),
+    ///     Err(err) => eprintln!("Could not perform a factory reset: {}", err),
+    /// };
+    /// #     Ok(())
+    /// # }
+    /// ```
+    ///
+    /// [`build_aes_key`]: #method.build_aes_key
+    fn factory_reset(&mut self, admin_pin: &str) -> Result<(), Error> {
+        let admin_pin_string = get_cstring(admin_pin)?;
+        get_command_result(unsafe { nitrokey_sys::NK_factory_reset(admin_pin_string.as_ptr()) })
+    }
+
+    /// Builds a new AES key on the Nitrokey.
+    ///
+    /// The AES key is used to encrypt the password safe and the encrypted volume.  You may need
+    /// to call this method after a factory reset, either using [`factory_reset`][] or using `gpg
+    /// --card-edit`.  You can also use it to destroy the data stored in the password safe or on
+    /// the encrypted volume.
+    ///
+    /// # Errors
+    ///
+    /// - [`InvalidString`][] if the provided password contains a null byte
+    /// - [`WrongPassword`][] if the admin password is wrong
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// use nitrokey::Device;
+    /// # use nitrokey::Error;
+    ///
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let mut device = manager.connect()?;
+    /// match device.build_aes_key("12345678") {
+    ///     Ok(()) => println!("New AES keys have been built."),
+    ///     Err(err) => eprintln!("Could not build new AES keys: {}", err),
+    /// };
+    /// #     Ok(())
+    /// # }
+    /// ```
+    ///
+    /// [`factory_reset`]: #method.factory_reset
+    fn build_aes_key(&mut self, admin_pin: &str) -> Result<(), Error> {
+        let admin_pin_string = get_cstring(admin_pin)?;
+        get_command_result(unsafe { nitrokey_sys::NK_build_aes_key(admin_pin_string.as_ptr()) })
+    }
+}
+
+fn get_connected_model() -> Option<Model> {
+    match unsafe { nitrokey_sys::NK_get_device_model() } {
+        nitrokey_sys::NK_device_model_NK_PRO => Some(Model::Pro),
+        nitrokey_sys::NK_device_model_NK_STORAGE => Some(Model::Storage),
+        _ => None,
+    }
+}
+
+pub(crate) fn create_device_wrapper(
+    manager: &mut crate::Manager,
+    model: Model,
+) -> DeviceWrapper<'_> {
+    match model {
+        Model::Pro => Pro::new(manager).into(),
+        Model::Storage => Storage::new(manager).into(),
+    }
+}
+
+pub(crate) fn get_connected_device(
+    manager: &mut crate::Manager,
+) -> Result<DeviceWrapper<'_>, Error> {
+    match get_connected_model() {
+        Some(model) => Ok(create_device_wrapper(manager, model)),
+        None => Err(CommunicationError::NotConnected.into()),
+    }
+}
+
+pub(crate) fn connect_enum(model: Model) -> bool {
+    let model = match model {
+        Model::Storage => nitrokey_sys::NK_device_model_NK_STORAGE,
+        Model::Pro => nitrokey_sys::NK_device_model_NK_PRO,
+    };
+    unsafe { nitrokey_sys::NK_login_enum(model) == 1 }
+}
diff --git a/src/device/pro.rs b/src/device/pro.rs
new file mode 100644
index 0000000..a65345e
--- /dev/null
+++ b/src/device/pro.rs
@@ -0,0 +1,79 @@
+// Copyright (C) 2018-2019 Robin Krahl <robin.krahl@ireas.org>
+// SPDX-License-Identifier: MIT
+
+use nitrokey_sys;
+
+use crate::device::{Device, Model};
+use crate::otp::GenerateOtp;
+
+/// A Nitrokey Pro device without user or admin authentication.
+///
+/// Use the [`connect`][] method to obtain an instance wrapper or the [`connect_pro`] method to
+/// directly obtain an instance.  If you want to execute a command that requires user or admin
+/// authentication, use [`authenticate_admin`][] or [`authenticate_user`][].
+///
+/// # Examples
+///
+/// Authentication with error handling:
+///
+/// ```no_run
+/// use nitrokey::{Authenticate, User, Pro};
+/// # use nitrokey::Error;
+///
+/// fn perform_user_task<'a>(device: &User<'a, Pro<'a>>) {}
+/// fn perform_other_task(device: &Pro) {}
+///
+/// # fn try_main() -> Result<(), Error> {
+/// let mut manager = nitrokey::take()?;
+/// let device = manager.connect_pro()?;
+/// let device = match device.authenticate_user("123456") {
+///     Ok(user) => {
+///         perform_user_task(&user);
+///         user.device()
+///     },
+///     Err((device, err)) => {
+///         eprintln!("Could not authenticate as user: {}", err);
+///         device
+///     },
+/// };
+/// perform_other_task(&device);
+/// #     Ok(())
+/// # }
+/// ```
+///
+/// [`authenticate_admin`]: trait.Authenticate.html#method.authenticate_admin
+/// [`authenticate_user`]: trait.Authenticate.html#method.authenticate_user
+/// [`connect`]: struct.Manager.html#method.connect
+/// [`connect_pro`]: struct.Manager.html#method.connect_pro
+#[derive(Debug)]
+pub struct Pro<'a> {
+    manager: Option<&'a mut crate::Manager>,
+}
+
+impl<'a> Pro<'a> {
+    pub(crate) fn new(manager: &'a mut crate::Manager) -> Pro<'a> {
+        Pro {
+            manager: Some(manager),
+        }
+    }
+}
+
+impl<'a> Drop for Pro<'a> {
+    fn drop(&mut self) {
+        unsafe {
+            nitrokey_sys::NK_logout();
+        }
+    }
+}
+
+impl<'a> Device<'a> for Pro<'a> {
+    fn into_manager(mut self) -> &'a mut crate::Manager {
+        self.manager.take().unwrap()
+    }
+
+    fn get_model(&self) -> Model {
+        Model::Pro
+    }
+}
+
+impl<'a> GenerateOtp for Pro<'a> {}
diff --git a/src/device/storage.rs b/src/device/storage.rs
new file mode 100644
index 0000000..370ce36
--- /dev/null
+++ b/src/device/storage.rs
@@ -0,0 +1,735 @@
+// Copyright (C) 2018-2019 Robin Krahl <robin.krahl@ireas.org>
+// SPDX-License-Identifier: MIT
+
+use std::fmt;
+
+use nitrokey_sys;
+
+use crate::device::{Device, FirmwareVersion, Model};
+use crate::error::Error;
+use crate::otp::GenerateOtp;
+use crate::util::{get_command_result, get_cstring};
+
+/// A Nitrokey Storage device without user or admin authentication.
+///
+/// Use the [`connect`][] method to obtain an instance wrapper or the [`connect_storage`] method to
+/// directly obtain an instance.  If you want to execute a command that requires user or admin
+/// authentication, use [`authenticate_admin`][] or [`authenticate_user`][].
+///
+/// # Examples
+///
+/// Authentication with error handling:
+///
+/// ```no_run
+/// use nitrokey::{Authenticate, User, Storage};
+/// # use nitrokey::Error;
+///
+/// fn perform_user_task<'a>(device: &User<'a, Storage<'a>>) {}
+/// fn perform_other_task(device: &Storage) {}
+///
+/// # fn try_main() -> Result<(), Error> {
+/// let mut manager = nitrokey::take()?;
+/// let device = manager.connect_storage()?;
+/// let device = match device.authenticate_user("123456") {
+///     Ok(user) => {
+///         perform_user_task(&user);
+///         user.device()
+///     },
+///     Err((device, err)) => {
+///         eprintln!("Could not authenticate as user: {}", err);
+///         device
+///     },
+/// };
+/// perform_other_task(&device);
+/// #     Ok(())
+/// # }
+/// ```
+///
+/// [`authenticate_admin`]: trait.Authenticate.html#method.authenticate_admin
+/// [`authenticate_user`]: trait.Authenticate.html#method.authenticate_user
+/// [`connect`]: struct.Manager.html#method.connect
+/// [`connect_storage`]: struct.Manager.html#method.connect_storage
+#[derive(Debug)]
+pub struct Storage<'a> {
+    manager: Option<&'a mut crate::Manager>,
+}
+
+/// The access mode of a volume on the Nitrokey Storage.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum VolumeMode {
+    /// A read-only volume.
+    ReadOnly,
+    /// A read-write volume.
+    ReadWrite,
+}
+
+impl fmt::Display for VolumeMode {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(match *self {
+            VolumeMode::ReadOnly => "read-only",
+            VolumeMode::ReadWrite => "read-write",
+        })
+    }
+}
+
+/// The status of a volume on a Nitrokey Storage device.
+#[derive(Debug)]
+pub struct VolumeStatus {
+    /// Indicates whether the volume is read-only.
+    pub read_only: bool,
+    /// Indicates whether the volume is active.
+    pub active: bool,
+}
+
+/// Information about the SD card in a Storage device.
+#[derive(Debug)]
+pub struct SdCardData {
+    /// The serial number of the SD card.
+    pub serial_number: u32,
+    /// The size of the SD card in GB.
+    pub size: u8,
+    /// The year the card was manufactured, e. g. 17 for 2017.
+    pub manufacturing_year: u8,
+    /// The month the card was manufactured.
+    pub manufacturing_month: u8,
+    /// The OEM ID.
+    pub oem: u16,
+    /// The manufacturer ID.
+    pub manufacturer: u8,
+}
+
+/// Production information for a Storage device.
+#[derive(Debug)]
+pub struct StorageProductionInfo {
+    /// The firmware version.
+    pub firmware_version: FirmwareVersion,
+    /// The internal firmware version.
+    pub firmware_version_internal: u8,
+    /// The serial number of the CPU.
+    pub serial_number_cpu: u32,
+    /// Information about the SD card.
+    pub sd_card: SdCardData,
+}
+
+/// The status of a Nitrokey Storage device.
+#[derive(Debug)]
+pub struct StorageStatus {
+    /// The status of the unencrypted volume.
+    pub unencrypted_volume: VolumeStatus,
+    /// The status of the encrypted volume.
+    pub encrypted_volume: VolumeStatus,
+    /// The status of the hidden volume.
+    pub hidden_volume: VolumeStatus,
+    /// The firmware version.
+    pub firmware_version: FirmwareVersion,
+    /// Indicates whether the firmware is locked.
+    pub firmware_locked: bool,
+    /// The serial number of the SD card in the Storage stick.
+    pub serial_number_sd_card: u32,
+    /// The serial number of the smart card in the Storage stick.
+    pub serial_number_smart_card: u32,
+    /// The number of remaining login attempts for the user PIN.
+    pub user_retry_count: u8,
+    /// The number of remaining login attempts for the admin PIN.
+    pub admin_retry_count: u8,
+    /// Indicates whether a new SD card was found.
+    pub new_sd_card_found: bool,
+    /// Indicates whether the SD card is filled with random characters.
+    pub filled_with_random: bool,
+    /// Indicates whether the stick has been initialized by generating
+    /// the AES keys.
+    pub stick_initialized: bool,
+}
+
+impl<'a> Storage<'a> {
+    pub(crate) fn new(manager: &'a mut crate::Manager) -> Storage<'a> {
+        Storage {
+            manager: Some(manager),
+        }
+    }
+
+    /// Changes the update PIN.
+    ///
+    /// The update PIN is used to enable firmware updates.  Unlike the user and the admin PIN, the
+    /// update PIN is not managed by the OpenPGP smart card but by the Nitrokey firmware.  There is
+    /// no retry counter as with the other PIN types.
+    ///
+    /// # Errors
+    ///
+    /// - [`InvalidString`][] if one of the provided passwords contains a null byte
+    /// - [`WrongPassword`][] if the current update password is wrong
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// # use nitrokey::Error;
+    ///
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let mut device = manager.connect_storage()?;
+    /// match device.change_update_pin("12345678", "87654321") {
+    ///     Ok(()) => println!("Updated update PIN."),
+    ///     Err(err) => eprintln!("Failed to update update PIN: {}", err),
+    /// };
+    /// #     Ok(())
+    /// # }
+    /// ```
+    ///
+    /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
+    /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
+    pub fn change_update_pin(&mut self, current: &str, new: &str) -> Result<(), Error> {
+        let current_string = get_cstring(current)?;
+        let new_string = get_cstring(new)?;
+        get_command_result(unsafe {
+            nitrokey_sys::NK_change_update_password(current_string.as_ptr(), new_string.as_ptr())
+        })
+    }
+
+    /// Enables the firmware update mode.
+    ///
+    /// During firmware update mode, the Nitrokey can no longer be accessed using HID commands.
+    /// To resume normal operation, run `dfu-programmer at32uc3a3256s launch`.  In order to enter
+    /// the firmware update mode, you need the update password that can be changed using the
+    /// [`change_update_pin`][] method.
+    ///
+    /// # Errors
+    ///
+    /// - [`InvalidString`][] if one of the provided passwords contains a null byte
+    /// - [`WrongPassword`][] if the current update password is wrong
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// # use nitrokey::Error;
+    ///
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let mut device = manager.connect_storage()?;
+    /// match device.enable_firmware_update("12345678") {
+    ///     Ok(()) => println!("Nitrokey entered update mode."),
+    ///     Err(err) => eprintln!("Could not enter update mode: {}", err),
+    /// };
+    /// #     Ok(())
+    /// # }
+    /// ```
+    ///
+    /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
+    /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
+    pub fn enable_firmware_update(&mut self, update_pin: &str) -> Result<(), Error> {
+        let update_pin_string = get_cstring(update_pin)?;
+        get_command_result(unsafe {
+            nitrokey_sys::NK_enable_firmware_update(update_pin_string.as_ptr())
+        })
+    }
+
+    /// Enables the encrypted storage volume.
+    ///
+    /// Once the encrypted volume is enabled, it is presented to the operating system as a block
+    /// device.  The API does not provide any information on the name or path of this block device.
+    ///
+    /// # Errors
+    ///
+    /// - [`InvalidString`][] if the provided password contains a null byte
+    /// - [`WrongPassword`][] if the provided user password is wrong
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// # use nitrokey::Error;
+    ///
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let mut device = manager.connect_storage()?;
+    /// match device.enable_encrypted_volume("123456") {
+    ///     Ok(()) => println!("Enabled the encrypted volume."),
+    ///     Err(err) => eprintln!("Could not enable the encrypted volume: {}", err),
+    /// };
+    /// #     Ok(())
+    /// # }
+    /// ```
+    ///
+    /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
+    /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
+    pub fn enable_encrypted_volume(&mut self, user_pin: &str) -> Result<(), Error> {
+        let user_pin = get_cstring(user_pin)?;
+        get_command_result(unsafe { nitrokey_sys::NK_unlock_encrypted_volume(user_pin.as_ptr()) })
+    }
+
+    /// Disables the encrypted storage volume.
+    ///
+    /// Once the volume is disabled, it can be no longer accessed as a block device.  If the
+    /// encrypted volume has not been enabled, this method still returns a success.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// # use nitrokey::Error;
+    ///
+    /// fn use_volume() {}
+    ///
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let mut device = manager.connect_storage()?;
+    /// match device.enable_encrypted_volume("123456") {
+    ///     Ok(()) => {
+    ///         println!("Enabled the encrypted volume.");
+    ///         use_volume();
+    ///         match device.disable_encrypted_volume() {
+    ///             Ok(()) => println!("Disabled the encrypted volume."),
+    ///             Err(err) => {
+    ///                 eprintln!("Could not disable the encrypted volume: {}", err);
+    ///             },
+    ///         };
+    ///     },
+    ///     Err(err) => eprintln!("Could not enable the encrypted volume: {}", err),
+    /// };
+    /// #     Ok(())
+    /// # }
+    /// ```
+    pub fn disable_encrypted_volume(&mut self) -> Result<(), Error> {
+        get_command_result(unsafe { nitrokey_sys::NK_lock_encrypted_volume() })
+    }
+
+    /// Enables a hidden storage volume.
+    ///
+    /// This function will only succeed if the encrypted storage ([`enable_encrypted_volume`][]) or
+    /// another hidden volume has been enabled previously.  Once the hidden volume is enabled, it
+    /// is presented to the operating system as a block device and any previously opened encrypted
+    /// or hidden volumes are closed.  The API does not provide any information on the name or path
+    /// of this block device.
+    ///
+    /// Note that the encrypted and the hidden volumes operate on the same storage area, so using
+    /// both at the same time might lead to data loss.
+    ///
+    /// The hidden volume to unlock is selected based on the provided password.
+    ///
+    /// # Errors
+    ///
+    /// - [`AesDecryptionFailed`][] if the encrypted storage has not been opened before calling
+    ///   this method or the AES key has not been built
+    /// - [`InvalidString`][] if the provided password contains a null byte
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// # use nitrokey::Error;
+    ///
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let mut device = manager.connect_storage()?;
+    /// device.enable_encrypted_volume("123445")?;
+    /// match device.enable_hidden_volume("hidden-pw") {
+    ///     Ok(()) => println!("Enabled a hidden volume."),
+    ///     Err(err) => eprintln!("Could not enable the hidden volume: {}", err),
+    /// };
+    /// #     Ok(())
+    /// # }
+    /// ```
+    ///
+    /// [`enable_encrypted_volume`]: #method.enable_encrypted_volume
+    /// [`AesDecryptionFailed`]: enum.CommandError.html#variant.AesDecryptionFailed
+    /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
+    pub fn enable_hidden_volume(&mut self, volume_password: &str) -> Result<(), Error> {
+        let volume_password = get_cstring(volume_password)?;
+        get_command_result(unsafe {
+            nitrokey_sys::NK_unlock_hidden_volume(volume_password.as_ptr())
+        })
+    }
+
+    /// Disables a hidden storage volume.
+    ///
+    /// Once the volume is disabled, it can be no longer accessed as a block device.  If no hidden
+    /// volume has been enabled, this method still returns a success.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// # use nitrokey::Error;
+    ///
+    /// fn use_volume() {}
+    ///
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let mut device = manager.connect_storage()?;
+    /// device.enable_encrypted_volume("123445")?;
+    /// match device.enable_hidden_volume("hidden-pw") {
+    ///     Ok(()) => {
+    ///         println!("Enabled the hidden volume.");
+    ///         use_volume();
+    ///         match device.disable_hidden_volume() {
+    ///             Ok(()) => println!("Disabled the hidden volume."),
+    ///             Err(err) => {
+    ///                 eprintln!("Could not disable the hidden volume: {}", err);
+    ///             },
+    ///         };
+    ///     },
+    ///     Err(err) => eprintln!("Could not enable the hidden volume: {}", err),
+    /// };
+    /// #     Ok(())
+    /// # }
+    /// ```
+    pub fn disable_hidden_volume(&mut self) -> Result<(), Error> {
+        get_command_result(unsafe { nitrokey_sys::NK_lock_hidden_volume() })
+    }
+
+    /// Creates a hidden volume.
+    ///
+    /// The volume is crated in the given slot and in the given range of the available memory,
+    /// where `start` is the start position as a percentage of the available memory, and `end` is
+    /// the end position as a percentage of the available memory.  The volume will be protected by
+    /// the given password.
+    ///
+    /// Note that the encrypted and the hidden volumes operate on the same storage area, so using
+    /// both at the same time might lead to data loss.
+    ///
+    /// According to the libnitrokey documentation, this function only works if the encrypted
+    /// storage has been opened.
+    ///
+    /// # Errors
+    ///
+    /// - [`AesDecryptionFailed`][] if the encrypted storage has not been opened before calling
+    ///   this method or the AES key has not been built
+    /// - [`InvalidString`][] if the provided password contains a null byte
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// # use nitrokey::Error;
+    ///
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let mut device = manager.connect_storage()?;
+    /// device.enable_encrypted_volume("123445")?;
+    /// device.create_hidden_volume(0, 0, 100, "hidden-pw")?;
+    /// #     Ok(())
+    /// # }
+    /// ```
+    ///
+    /// [`AesDecryptionFailed`]: enum.CommandError.html#variant.AesDecryptionFailed
+    /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
+    pub fn create_hidden_volume(
+        &mut self,
+        slot: u8,
+        start: u8,
+        end: u8,
+        password: &str,
+    ) -> Result<(), Error> {
+        let password = get_cstring(password)?;
+        get_command_result(unsafe {
+            nitrokey_sys::NK_create_hidden_volume(slot, start, end, password.as_ptr())
+        })
+    }
+
+    /// Sets the access mode of the unencrypted volume.
+    ///
+    /// This command will reconnect the unencrypted volume so buffers should be flushed before
+    /// calling it.  Since firmware version v0.51, this command requires the admin PIN.  Older
+    /// firmware versions are not supported.
+    ///
+    /// # Errors
+    ///
+    /// - [`InvalidString`][] if the provided password contains a null byte
+    /// - [`WrongPassword`][] if the provided admin password is wrong
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// # use nitrokey::Error;
+    /// use nitrokey::VolumeMode;
+    ///
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let mut device = manager.connect_storage()?;
+    /// match device.set_unencrypted_volume_mode("12345678", VolumeMode::ReadWrite) {
+    ///     Ok(()) => println!("Set the unencrypted volume to read-write mode."),
+    ///     Err(err) => eprintln!("Could not set the unencrypted volume to read-write mode: {}", err),
+    /// };
+    /// #     Ok(())
+    /// # }
+    /// ```
+    ///
+    /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
+    /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
+    pub fn set_unencrypted_volume_mode(
+        &mut self,
+        admin_pin: &str,
+        mode: VolumeMode,
+    ) -> Result<(), Error> {
+        let admin_pin = get_cstring(admin_pin)?;
+        let result = match mode {
+            VolumeMode::ReadOnly => unsafe {
+                nitrokey_sys::NK_set_unencrypted_read_only_admin(admin_pin.as_ptr())
+            },
+            VolumeMode::ReadWrite => unsafe {
+                nitrokey_sys::NK_set_unencrypted_read_write_admin(admin_pin.as_ptr())
+            },
+        };
+        get_command_result(result)
+    }
+
+    /// Sets the access mode of the encrypted volume.
+    ///
+    /// This command will reconnect the encrypted volume so buffers should be flushed before
+    /// calling it.  It is only available in firmware version 0.49.
+    ///
+    /// # Errors
+    ///
+    /// - [`InvalidString`][] if the provided password contains a null byte
+    /// - [`WrongPassword`][] if the provided admin password is wrong
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// # use nitrokey::Error;
+    /// use nitrokey::VolumeMode;
+    ///
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let mut device = manager.connect_storage()?;
+    /// match device.set_encrypted_volume_mode("12345678", VolumeMode::ReadWrite) {
+    ///     Ok(()) => println!("Set the encrypted volume to read-write mode."),
+    ///     Err(err) => eprintln!("Could not set the encrypted volume to read-write mode: {}", err),
+    /// };
+    /// #     Ok(())
+    /// # }
+    /// ```
+    ///
+    /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
+    /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
+    pub fn set_encrypted_volume_mode(
+        &mut self,
+        admin_pin: &str,
+        mode: VolumeMode,
+    ) -> Result<(), Error> {
+        let admin_pin = get_cstring(admin_pin)?;
+        let result = match mode {
+            VolumeMode::ReadOnly => unsafe {
+                nitrokey_sys::NK_set_encrypted_read_only(admin_pin.as_ptr())
+            },
+            VolumeMode::ReadWrite => unsafe {
+                nitrokey_sys::NK_set_encrypted_read_write(admin_pin.as_ptr())
+            },
+        };
+        get_command_result(result)
+    }
+
+    /// Returns the status of the connected storage device.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// # use nitrokey::Error;
+    ///
+    /// fn use_volume() {}
+    ///
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let device = manager.connect_storage()?;
+    /// match device.get_status() {
+    ///     Ok(status) => {
+    ///         println!("SD card ID: {:#x}", status.serial_number_sd_card);
+    ///     },
+    ///     Err(err) => eprintln!("Could not get Storage status: {}", err),
+    /// };
+    /// #     Ok(())
+    /// # }
+    /// ```
+    pub fn get_status(&self) -> Result<StorageStatus, Error> {
+        let mut raw_status = nitrokey_sys::NK_storage_status {
+            unencrypted_volume_read_only: false,
+            unencrypted_volume_active: false,
+            encrypted_volume_read_only: false,
+            encrypted_volume_active: false,
+            hidden_volume_read_only: false,
+            hidden_volume_active: false,
+            firmware_version_major: 0,
+            firmware_version_minor: 0,
+            firmware_locked: false,
+            serial_number_sd_card: 0,
+            serial_number_smart_card: 0,
+            user_retry_count: 0,
+            admin_retry_count: 0,
+            new_sd_card_found: false,
+            filled_with_random: false,
+            stick_initialized: false,
+        };
+        let raw_result = unsafe { nitrokey_sys::NK_get_status_storage(&mut raw_status) };
+        get_command_result(raw_result).map(|_| StorageStatus::from(raw_status))
+    }
+
+    /// Returns the production information for the connected storage device.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// # use nitrokey::Error;
+    ///
+    /// fn use_volume() {}
+    ///
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let device = manager.connect_storage()?;
+    /// match device.get_production_info() {
+    ///     Ok(data) => {
+    ///         println!("SD card ID:   {:#x}", data.sd_card.serial_number);
+    ///         println!("SD card size: {} GB", data.sd_card.size);
+    ///     },
+    ///     Err(err) => eprintln!("Could not get Storage production info: {}", err),
+    /// };
+    /// #     Ok(())
+    /// # }
+    /// ```
+    pub fn get_production_info(&self) -> Result<StorageProductionInfo, Error> {
+        let mut raw_data = nitrokey_sys::NK_storage_ProductionTest {
+            FirmwareVersion_au8: [0, 2],
+            FirmwareVersionInternal_u8: 0,
+            SD_Card_Size_u8: 0,
+            CPU_CardID_u32: 0,
+            SmartCardID_u32: 0,
+            SD_CardID_u32: 0,
+            SC_UserPwRetryCount: 0,
+            SC_AdminPwRetryCount: 0,
+            SD_Card_ManufacturingYear_u8: 0,
+            SD_Card_ManufacturingMonth_u8: 0,
+            SD_Card_OEM_u16: 0,
+            SD_WriteSpeed_u16: 0,
+            SD_Card_Manufacturer_u8: 0,
+        };
+        let raw_result = unsafe { nitrokey_sys::NK_get_storage_production_info(&mut raw_data) };
+        get_command_result(raw_result).map(|_| StorageProductionInfo::from(raw_data))
+    }
+
+    /// Clears the warning for a new SD card.
+    ///
+    /// The Storage status contains a field for a new SD card warning.  After a factory reset, the
+    /// field is set to true.  After filling the SD card with random data, it is set to false.
+    /// This method can be used to set it to false without filling the SD card with random data.
+    ///
+    /// # Errors
+    ///
+    /// - [`InvalidString`][] if the provided password contains a null byte
+    /// - [`WrongPassword`][] if the provided admin password is wrong
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// # use nitrokey::Error;
+    ///
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let mut device = manager.connect_storage()?;
+    /// match device.clear_new_sd_card_warning("12345678") {
+    ///     Ok(()) => println!("Cleared the new SD card warning."),
+    ///     Err(err) => eprintln!("Could not set the clear the new SD card warning: {}", err),
+    /// };
+    /// #     Ok(())
+    /// # }
+    /// ```
+    ///
+    /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
+    /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
+    pub fn clear_new_sd_card_warning(&mut self, admin_pin: &str) -> Result<(), Error> {
+        let admin_pin = get_cstring(admin_pin)?;
+        get_command_result(unsafe {
+            nitrokey_sys::NK_clear_new_sd_card_warning(admin_pin.as_ptr())
+        })
+    }
+
+    /// Blinks the red and green LED alternatively and infinitely until the device is reconnected.
+    pub fn wink(&mut self) -> Result<(), Error> {
+        get_command_result(unsafe { nitrokey_sys::NK_wink() })
+    }
+
+    /// Exports the firmware to the unencrypted volume.
+    ///
+    /// This command requires the admin PIN.  The unencrypted volume must be in read-write mode
+    /// when this command is executed.  Otherwise, it will still return `Ok` but not write the
+    /// firmware.
+    ///
+    /// This command unmounts the unencrypted volume if it has been mounted, so all buffers should
+    /// be flushed.  The firmware is written to the `firmware.bin` file on the unencrypted volume.
+    ///
+    /// # Errors
+    ///
+    /// - [`InvalidString`][] if one of the provided passwords contains a null byte
+    /// - [`WrongPassword`][] if the admin password is wrong
+    ///
+    /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
+    /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
+    pub fn export_firmware(&mut self, admin_pin: &str) -> Result<(), Error> {
+        let admin_pin_string = get_cstring(admin_pin)?;
+        get_command_result(unsafe { nitrokey_sys::NK_export_firmware(admin_pin_string.as_ptr()) })
+    }
+}
+
+impl<'a> Drop for Storage<'a> {
+    fn drop(&mut self) {
+        unsafe {
+            nitrokey_sys::NK_logout();
+        }
+    }
+}
+
+impl<'a> Device<'a> for Storage<'a> {
+    fn into_manager(mut self) -> &'a mut crate::Manager {
+        self.manager.take().unwrap()
+    }
+
+    fn get_model(&self) -> Model {
+        Model::Storage
+    }
+}
+
+impl<'a> GenerateOtp for Storage<'a> {}
+
+impl From<nitrokey_sys::NK_storage_ProductionTest> for StorageProductionInfo {
+    fn from(data: nitrokey_sys::NK_storage_ProductionTest) -> Self {
+        Self {
+            firmware_version: FirmwareVersion {
+                major: data.FirmwareVersion_au8[0],
+                minor: data.FirmwareVersion_au8[1],
+            },
+            firmware_version_internal: data.FirmwareVersionInternal_u8,
+            serial_number_cpu: data.CPU_CardID_u32,
+            sd_card: SdCardData {
+                serial_number: data.SD_CardID_u32,
+                size: data.SD_Card_Size_u8,
+                manufacturing_year: data.SD_Card_ManufacturingYear_u8,
+                manufacturing_month: data.SD_Card_ManufacturingMonth_u8,
+                oem: data.SD_Card_OEM_u16,
+                manufacturer: data.SD_Card_Manufacturer_u8,
+            },
+        }
+    }
+}
+
+impl From<nitrokey_sys::NK_storage_status> for StorageStatus {
+    fn from(status: nitrokey_sys::NK_storage_status) -> Self {
+        StorageStatus {
+            unencrypted_volume: VolumeStatus {
+                read_only: status.unencrypted_volume_read_only,
+                active: status.unencrypted_volume_active,
+            },
+            encrypted_volume: VolumeStatus {
+                read_only: status.encrypted_volume_read_only,
+                active: status.encrypted_volume_active,
+            },
+            hidden_volume: VolumeStatus {
+                read_only: status.hidden_volume_read_only,
+                active: status.hidden_volume_active,
+            },
+            firmware_version: FirmwareVersion {
+                major: status.firmware_version_major,
+                minor: status.firmware_version_minor,
+            },
+            firmware_locked: status.firmware_locked,
+            serial_number_sd_card: status.serial_number_sd_card,
+            serial_number_smart_card: status.serial_number_smart_card,
+            user_retry_count: status.user_retry_count,
+            admin_retry_count: status.admin_retry_count,
+            new_sd_card_found: status.new_sd_card_found,
+            filled_with_random: status.filled_with_random,
+            stick_initialized: status.stick_initialized,
+        }
+    }
+}
diff --git a/src/device/wrapper.rs b/src/device/wrapper.rs
new file mode 100644
index 0000000..a3a18f9
--- /dev/null
+++ b/src/device/wrapper.rs
@@ -0,0 +1,134 @@
+// Copyright (C) 2018-2019 Robin Krahl <robin.krahl@ireas.org>
+// SPDX-License-Identifier: MIT
+
+use crate::device::{Device, Model, Pro, Storage};
+use crate::error::Error;
+use crate::otp::GenerateOtp;
+
+/// A wrapper for a Nitrokey device of unknown type.
+///
+/// Use the [`connect`][] method to obtain a wrapped instance.  The wrapper implements all traits
+/// that are shared between all Nitrokey devices so that the shared functionality can be used
+/// without knowing the type of the underlying device.  If you want to use functionality that is
+/// not available for all devices, you have to extract the device.
+///
+/// # Examples
+///
+/// Authentication with error handling:
+///
+/// ```no_run
+/// use nitrokey::{Authenticate, DeviceWrapper, User};
+/// # use nitrokey::Error;
+///
+/// fn perform_user_task<'a>(device: &User<'a, DeviceWrapper<'a>>) {}
+/// fn perform_other_task(device: &DeviceWrapper) {}
+///
+/// # fn try_main() -> Result<(), Error> {
+/// let mut manager = nitrokey::take()?;
+/// let device = manager.connect()?;
+/// let device = match device.authenticate_user("123456") {
+///     Ok(user) => {
+///         perform_user_task(&user);
+///         user.device()
+///     },
+///     Err((device, err)) => {
+///         eprintln!("Could not authenticate as user: {}", err);
+///         device
+///     },
+/// };
+/// perform_other_task(&device);
+/// #     Ok(())
+/// # }
+/// ```
+///
+/// Device-specific commands:
+///
+/// ```no_run
+/// use nitrokey::{DeviceWrapper, Storage};
+/// # use nitrokey::Error;
+///
+/// fn perform_common_task(device: &DeviceWrapper) {}
+/// fn perform_storage_task(device: &Storage) {}
+///
+/// # fn try_main() -> Result<(), Error> {
+/// let mut manager = nitrokey::take()?;
+/// let device = manager.connect()?;
+/// perform_common_task(&device);
+/// match device {
+///     DeviceWrapper::Storage(storage) => perform_storage_task(&storage),
+///     _ => (),
+/// };
+/// #     Ok(())
+/// # }
+/// ```
+///
+/// [`connect`]: struct.Manager.html#method.connect
+#[derive(Debug)]
+pub enum DeviceWrapper<'a> {
+    /// A Nitrokey Storage device.
+    Storage(Storage<'a>),
+    /// A Nitrokey Pro device.
+    Pro(Pro<'a>),
+}
+
+impl<'a> DeviceWrapper<'a> {
+    fn device(&self) -> &dyn Device<'a> {
+        match *self {
+            DeviceWrapper::Storage(ref storage) => storage,
+            DeviceWrapper::Pro(ref pro) => pro,
+        }
+    }
+
+    fn device_mut(&mut self) -> &mut dyn Device<'a> {
+        match *self {
+            DeviceWrapper::Storage(ref mut storage) => storage,
+            DeviceWrapper::Pro(ref mut pro) => pro,
+        }
+    }
+}
+
+impl<'a> From<Pro<'a>> for DeviceWrapper<'a> {
+    fn from(device: Pro<'a>) -> Self {
+        DeviceWrapper::Pro(device)
+    }
+}
+
+impl<'a> From<Storage<'a>> for DeviceWrapper<'a> {
+    fn from(device: Storage<'a>) -> Self {
+        DeviceWrapper::Storage(device)
+    }
+}
+
+impl<'a> GenerateOtp for DeviceWrapper<'a> {
+    fn get_hotp_slot_name(&self, slot: u8) -> Result<String, Error> {
+        self.device().get_hotp_slot_name(slot)
+    }
+
+    fn get_totp_slot_name(&self, slot: u8) -> Result<String, Error> {
+        self.device().get_totp_slot_name(slot)
+    }
+
+    fn get_hotp_code(&mut self, slot: u8) -> Result<String, Error> {
+        self.device_mut().get_hotp_code(slot)
+    }
+
+    fn get_totp_code(&self, slot: u8) -> Result<String, Error> {
+        self.device().get_totp_code(slot)
+    }
+}
+
+impl<'a> Device<'a> for DeviceWrapper<'a> {
+    fn into_manager(self) -> &'a mut crate::Manager {
+        match self {
+            DeviceWrapper::Pro(dev) => dev.into_manager(),
+            DeviceWrapper::Storage(dev) => dev.into_manager(),
+        }
+    }
+
+    fn get_model(&self) -> Model {
+        match *self {
+            DeviceWrapper::Pro(_) => Model::Pro,
+            DeviceWrapper::Storage(_) => Model::Storage,
+        }
+    }
+}
diff --git a/src/error.rs b/src/error.rs
new file mode 100644
index 0000000..9e6adc0
--- /dev/null
+++ b/src/error.rs
@@ -0,0 +1,269 @@
+// Copyright (C) 2019 Robin Krahl <robin.krahl@ireas.org>
+// SPDX-License-Identifier: MIT
+
+use std::error;
+use std::fmt;
+use std::os::raw;
+use std::str;
+use std::sync;
+
+use crate::device;
+
+/// An error returned by the nitrokey crate.
+#[derive(Debug)]
+pub enum Error {
+    /// An error reported by the Nitrokey device in the response packet.
+    CommandError(CommandError),
+    /// A device communication error.
+    CommunicationError(CommunicationError),
+    /// An error occurred due to concurrent access to the Nitrokey device.
+    ConcurrentAccessError,
+    /// A library usage error.
+    LibraryError(LibraryError),
+    /// An error that occurred due to a poisoned lock.
+    PoisonError(sync::PoisonError<sync::MutexGuard<'static, crate::Manager>>),
+    /// An error that occurred during random number generation.
+    RandError(Box<dyn error::Error>),
+    /// An error that is caused by an unexpected value returned by libnitrokey.
+    UnexpectedError,
+    /// An unknown error returned by libnitrokey.
+    UnknownError(i64),
+    /// An error occurred when interpreting a UTF-8 string.
+    Utf8Error(str::Utf8Error),
+}
+
+impl From<raw::c_int> for Error {
+    fn from(code: raw::c_int) -> Self {
+        if let Some(err) = CommandError::try_from(code) {
+            Error::CommandError(err)
+        } else if let Some(err) = CommunicationError::try_from(256 - code) {
+            Error::CommunicationError(err)
+        } else if let Some(err) = LibraryError::try_from(code) {
+            Error::LibraryError(err)
+        } else {
+            Error::UnknownError(code.into())
+        }
+    }
+}
+
+impl From<CommandError> for Error {
+    fn from(err: CommandError) -> Self {
+        Error::CommandError(err)
+    }
+}
+
+impl From<CommunicationError> for Error {
+    fn from(err: CommunicationError) -> Self {
+        Error::CommunicationError(err)
+    }
+}
+
+impl From<LibraryError> for Error {
+    fn from(err: LibraryError) -> Self {
+        Error::LibraryError(err)
+    }
+}
+
+impl From<str::Utf8Error> for Error {
+    fn from(error: str::Utf8Error) -> Self {
+        Error::Utf8Error(error)
+    }
+}
+
+impl From<sync::PoisonError<sync::MutexGuard<'static, crate::Manager>>> for Error {
+    fn from(error: sync::PoisonError<sync::MutexGuard<'static, crate::Manager>>) -> Self {
+        Error::PoisonError(error)
+    }
+}
+
+impl From<sync::TryLockError<sync::MutexGuard<'static, crate::Manager>>> for Error {
+    fn from(error: sync::TryLockError<sync::MutexGuard<'static, crate::Manager>>) -> Self {
+        match error {
+            sync::TryLockError::Poisoned(err) => err.into(),
+            sync::TryLockError::WouldBlock => Error::ConcurrentAccessError,
+        }
+    }
+}
+
+impl<'a, T: device::Device<'a>> From<(T, Error)> for Error {
+    fn from((_, err): (T, Error)) -> Self {
+        err
+    }
+}
+
+impl error::Error for Error {
+    fn source(&self) -> Option<&(dyn error::Error + 'static)> {
+        match *self {
+            Error::CommandError(ref err) => Some(err),
+            Error::CommunicationError(ref err) => Some(err),
+            Error::ConcurrentAccessError => None,
+            Error::LibraryError(ref err) => Some(err),
+            Error::PoisonError(ref err) => Some(err),
+            Error::RandError(ref err) => Some(err.as_ref()),
+            Error::UnexpectedError => None,
+            Error::UnknownError(_) => None,
+            Error::Utf8Error(ref err) => Some(err),
+        }
+    }
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match *self {
+            Error::CommandError(ref err) => write!(f, "Command error: {}", err),
+            Error::CommunicationError(ref err) => write!(f, "Communication error: {}", err),
+            Error::ConcurrentAccessError => write!(f, "Internal error: concurrent access"),
+            Error::LibraryError(ref err) => write!(f, "Library error: {}", err),
+            Error::PoisonError(_) => write!(f, "Internal error: poisoned lock"),
+            Error::RandError(ref err) => write!(f, "RNG error: {}", err),
+            Error::UnexpectedError => write!(f, "An unexpected error occurred"),
+            Error::UnknownError(ref err) => write!(f, "Unknown error: {}", err),
+            Error::Utf8Error(ref err) => write!(f, "UTF-8 error: {}", err),
+        }
+    }
+}
+
+/// An error reported by the Nitrokey device in the response packet.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum CommandError {
+    /// A packet with a wrong checksum has been sent or received.
+    WrongCrc,
+    /// A command tried to access an OTP slot that does not exist.
+    WrongSlot,
+    /// A command tried to generate an OTP on a slot that is not configured.
+    SlotNotProgrammed,
+    /// The provided password is wrong.
+    WrongPassword,
+    /// You are not authorized for this command or provided a wrong temporary
+    /// password.
+    NotAuthorized,
+    /// An error occurred when getting or setting the time.
+    Timestamp,
+    /// You did not provide a name for the OTP slot.
+    NoName,
+    /// This command is not supported by this device.
+    NotSupported,
+    /// This command is unknown.
+    UnknownCommand,
+    /// AES decryption failed.
+    AesDecryptionFailed,
+}
+
+impl CommandError {
+    fn try_from(value: raw::c_int) -> Option<Self> {
+        match value {
+            1 => Some(CommandError::WrongCrc),
+            2 => Some(CommandError::WrongSlot),
+            3 => Some(CommandError::SlotNotProgrammed),
+            4 => Some(CommandError::WrongPassword),
+            5 => Some(CommandError::NotAuthorized),
+            6 => Some(CommandError::Timestamp),
+            7 => Some(CommandError::NoName),
+            8 => Some(CommandError::NotSupported),
+            9 => Some(CommandError::UnknownCommand),
+            10 => Some(CommandError::AesDecryptionFailed),
+            _ => None,
+        }
+    }
+}
+
+impl error::Error for CommandError {}
+
+impl fmt::Display for CommandError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(match *self {
+            CommandError::WrongCrc => "A packet with a wrong checksum has been sent or received",
+            CommandError::WrongSlot => "The given slot does not exist",
+            CommandError::SlotNotProgrammed => "The given slot is not programmed",
+            CommandError::WrongPassword => "The given password is wrong",
+            CommandError::NotAuthorized => {
+                "You are not authorized for this command or provided a wrong temporary \
+                 password"
+            }
+            CommandError::Timestamp => "An error occurred when getting or setting the time",
+            CommandError::NoName => "You did not provide a name for the slot",
+            CommandError::NotSupported => "This command is not supported by this device",
+            CommandError::UnknownCommand => "This command is unknown",
+            CommandError::AesDecryptionFailed => "AES decryption failed",
+        })
+    }
+}
+
+/// A device communication error.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum CommunicationError {
+    /// Could not connect to a Nitrokey device.
+    NotConnected,
+    /// Sending a packet failed.
+    SendingFailure,
+    /// Receiving a packet failed.
+    ReceivingFailure,
+    /// A packet with a wrong checksum was received.
+    InvalidCrc,
+}
+
+impl CommunicationError {
+    fn try_from(value: raw::c_int) -> Option<Self> {
+        match value {
+            2 => Some(CommunicationError::NotConnected),
+            3 => Some(CommunicationError::SendingFailure),
+            4 => Some(CommunicationError::ReceivingFailure),
+            5 => Some(CommunicationError::InvalidCrc),
+            _ => None,
+        }
+    }
+}
+
+impl error::Error for CommunicationError {}
+
+impl fmt::Display for CommunicationError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(match *self {
+            CommunicationError::NotConnected => "Could not connect to a Nitrokey device",
+            CommunicationError::SendingFailure => "Sending a packet failed",
+            CommunicationError::ReceivingFailure => "Receiving a packet failed",
+            CommunicationError::InvalidCrc => "A packet with a wrong checksum was received",
+        })
+    }
+}
+
+/// A library usage error.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum LibraryError {
+    /// A supplied string exceeded a length limit.
+    StringTooLong,
+    /// You passed an invalid slot.
+    InvalidSlot,
+    /// The supplied string was not in hexadecimal format.
+    InvalidHexString,
+    /// The target buffer was smaller than the source.
+    TargetBufferTooSmall,
+    /// You passed a string containing a null byte.
+    InvalidString,
+}
+
+impl LibraryError {
+    fn try_from(value: raw::c_int) -> Option<Self> {
+        match value {
+            200 => Some(LibraryError::StringTooLong),
+            201 => Some(LibraryError::InvalidSlot),
+            202 => Some(LibraryError::InvalidHexString),
+            203 => Some(LibraryError::TargetBufferTooSmall),
+            _ => None,
+        }
+    }
+}
+
+impl error::Error for LibraryError {}
+
+impl fmt::Display for LibraryError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(match *self {
+            LibraryError::StringTooLong => "The supplied string is too long",
+            LibraryError::InvalidSlot => "The given slot is invalid",
+            LibraryError::InvalidHexString => "The supplied string is not in hexadecimal format",
+            LibraryError::TargetBufferTooSmall => "The target buffer is too small",
+            LibraryError::InvalidString => "You passed a string containing a null byte",
+        })
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index 02a622b..059792d 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,3 +1,6 @@
+// Copyright (C) 2018-2019 Robin Krahl <robin.krahl@ireas.org>
+// SPDX-License-Identifier: MIT
+
 //! Provides access to a Nitrokey device using the native libnitrokey API.
 //!
 //! # Usage
@@ -6,13 +9,16 @@
 //! performed without authentication, some require user access, and some require admin access.
 //! This is modelled using the types [`User`][] and [`Admin`][].
 //!
-//! Use [`connect`][] to connect to any Nitrokey device.  The method will return a
+//! You can only connect to one Nitrokey at a time.  Use the global [`take`][] function to obtain
+//! an reference to the [`Manager`][] singleton that keeps track of the connections.  Then use the
+//! [`connect`][] method to connect to any Nitrokey device.  The method will return a
 //! [`DeviceWrapper`][] that abstracts over the supported Nitrokey devices.  You can also use
-//! [`Pro::connect`][] or [`Storage::connect`][] to connect to a specific device.
+//! [`connect_model`][], [`connect_pro`][] or [`connect_storage`][] to connect to a specific
+//! device.
 //!
-//! You can then use [`authenticate_user`][] or [`authenticate_admin`][] to get an authenticated
-//! device that can perform operations that require authentication.  You can use [`device`][] to go
-//! back to the unauthenticated device.
+//! You can call [`authenticate_user`][] or [`authenticate_admin`][] to get an authenticated device
+//! that can perform operations that require authentication.  You can use [`device`][] to go back
+//! to the unauthenticated device.
 //!
 //! This makes sure that you can only execute a command if you have the required access rights.
 //! Otherwise, your code will not compile.  The only exception are the methods to generate one-time
@@ -25,10 +31,11 @@
 //!
 //! ```no_run
 //! use nitrokey::Device;
-//! # use nitrokey::CommandError;
+//! # use nitrokey::Error;
 //!
-//! # fn try_main() -> Result<(), CommandError> {
-//! let device = nitrokey::connect()?;
+//! # fn try_main() -> Result<(), Error> {
+//! let mut manager = nitrokey::take()?;
+//! let device = manager.connect()?;
 //! println!("{}", device.get_serial_number()?);
 //! #     Ok(())
 //! # }
@@ -38,19 +45,20 @@
 //!
 //! ```no_run
 //! use nitrokey::{Authenticate, ConfigureOtp, OtpMode, OtpSlotData};
-//! # use nitrokey::CommandError;
+//! # use nitrokey::Error;
 //!
-//! # fn try_main() -> Result<(), (CommandError)> {
-//! let device = nitrokey::connect()?;
+//! # fn try_main() -> Result<(), Error> {
+//! let mut manager = nitrokey::take()?;
+//! let device = manager.connect()?;
 //! let slot_data = OtpSlotData::new(1, "test", "01234567890123456689", OtpMode::SixDigits);
 //! match device.authenticate_admin("12345678") {
-//!     Ok(admin) => {
+//!     Ok(mut admin) => {
 //!         match admin.write_hotp_slot(slot_data, 0) {
 //!             Ok(()) => println!("Successfully wrote slot."),
-//!             Err(err) => println!("Could not write slot: {}", err),
+//!             Err(err) => eprintln!("Could not write slot: {}", err),
 //!         }
 //!     },
-//!     Err((_, err)) => println!("Could not authenticate as admin: {}", err),
+//!     Err((_, err)) => eprintln!("Could not authenticate as admin: {}", err),
 //! }
 //! #     Ok(())
 //! # }
@@ -60,13 +68,14 @@
 //!
 //! ```no_run
 //! use nitrokey::{Device, GenerateOtp};
-//! # use nitrokey::CommandError;
+//! # use nitrokey::Error;
 //!
-//! # fn try_main() -> Result<(), (CommandError)> {
-//! let device = nitrokey::connect()?;
+//! # fn try_main() -> Result<(), Error> {
+//! let mut manager = nitrokey::take()?;
+//! let mut device = manager.connect()?;
 //! match device.get_hotp_code(1) {
 //!     Ok(code) => println!("Generated HOTP code: {}", code),
-//!     Err(err) => println!("Could not generate HOTP code: {}", err),
+//!     Err(err) => eprintln!("Could not generate HOTP code: {}", err),
 //! }
 //! #     Ok(())
 //! # }
@@ -74,9 +83,12 @@
 //!
 //! [`authenticate_admin`]: trait.Authenticate.html#method.authenticate_admin
 //! [`authenticate_user`]: trait.Authenticate.html#method.authenticate_user
-//! [`connect`]: fn.connect.html
-//! [`Pro::connect`]: struct.Pro.html#fn.connect.html
-//! [`Storage::connect`]: struct.Storage.html#fn.connect.html
+//! [`take`]: fn.take.html
+//! [`connect`]: struct.Manager.html#method.connect
+//! [`connect_model`]: struct.Manager.html#method.connect_model
+//! [`connect_pro`]: struct.Manager.html#method.connect_pro
+//! [`connect_storage`]: struct.Manager.html#method.connect_storage
+//! [`manager`]: trait.Device.html#method.manager
 //! [`device`]: struct.User.html#method.device
 //! [`get_hotp_code`]: trait.GenerateOtp.html#method.get_hotp_code
 //! [`get_totp_code`]: trait.GenerateOtp.html#method.get_totp_code
@@ -86,24 +98,42 @@
 
 #![warn(missing_docs, rust_2018_compatibility, rust_2018_idioms, unused)]
 
+#[macro_use(lazy_static)]
+extern crate lazy_static;
+
 mod auth;
 mod config;
 mod device;
+mod error;
 mod otp;
 mod pws;
 mod util;
 
+use std::fmt;
+use std::marker;
+use std::sync;
+
 use nitrokey_sys;
 
 pub use crate::auth::{Admin, Authenticate, User};
 pub use crate::config::Config;
 pub use crate::device::{
-    connect, connect_model, Device, DeviceWrapper, Model, Pro, SdCardData, Storage,
-    StorageProductionInfo, StorageStatus, VolumeMode, VolumeStatus,
+    Device, DeviceWrapper, Model, Pro, SdCardData, Storage, StorageProductionInfo, StorageStatus,
+    VolumeMode, VolumeStatus,
 };
+pub use crate::error::{CommandError, CommunicationError, Error, LibraryError};
 pub use crate::otp::{ConfigureOtp, GenerateOtp, OtpMode, OtpSlotData};
 pub use crate::pws::{GetPasswordSafe, PasswordSafe, SLOT_COUNT};
-pub use crate::util::{CommandError, LogLevel};
+pub use crate::util::LogLevel;
+
+/// The default admin PIN for all Nitrokey devices.
+pub const DEFAULT_ADMIN_PIN: &str = "12345678";
+/// The default user PIN for all Nitrokey devices.
+pub const DEFAULT_USER_PIN: &str = "123456";
+
+lazy_static! {
+    static ref MANAGER: sync::Mutex<Manager> = sync::Mutex::new(Manager::new());
+}
 
 /// A version of the libnitrokey library.
 ///
@@ -125,6 +155,265 @@ pub struct Version {
     pub minor: u32,
 }
 
+impl fmt::Display for Version {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if self.git.is_empty() {
+            write!(f, "v{}.{}", self.major, self.minor)
+        } else {
+            f.write_str(&self.git)
+        }
+    }
+}
+
+/// A manager for connections to Nitrokey devices.
+///
+/// Currently, libnitrokey only provides access to one Nitrokey device at the same time.  This
+/// manager struct makes sure that `nitrokey-rs` does not try to connect to two devices at the same
+/// time.
+///
+/// To obtain a reference to an instance of this manager, use the [`take`][] function.  Use one of
+/// the connect methods – [`connect`][], [`connect_model`][], [`connect_pro`][] or
+/// [`connect_storage`][] – to retrieve a [`Device`][] instance.
+///
+/// # Examples
+///
+/// Connect to a single device:
+///
+/// ```no_run
+/// use nitrokey::Device;
+/// # use nitrokey::Error;
+///
+/// # fn try_main() -> Result<(), Error> {
+/// let mut manager = nitrokey::take()?;
+/// let device = manager.connect()?;
+/// println!("{}", device.get_serial_number()?);
+/// #     Ok(())
+/// # }
+/// ```
+///
+/// Connect to a Pro and a Storage device:
+///
+/// ```no_run
+/// use nitrokey::{Device, Model};
+/// # use nitrokey::Error;
+///
+/// # fn try_main() -> Result<(), Error> {
+/// let mut manager = nitrokey::take()?;
+/// let device = manager.connect_model(Model::Pro)?;
+/// println!("Pro: {}", device.get_serial_number()?);
+/// drop(device);
+/// let device = manager.connect_model(Model::Storage)?;
+/// println!("Storage: {}", device.get_serial_number()?);
+/// #     Ok(())
+/// # }
+/// ```
+///
+/// [`connect`]: #method.connect
+/// [`connect_model`]: #method.connect_model
+/// [`connect_pro`]: #method.connect_pro
+/// [`connect_storage`]: #method.connect_storage
+/// [`manager`]: trait.Device.html#method.manager
+/// [`take`]: fn.take.html
+/// [`Device`]: trait.Device.html
+#[derive(Debug)]
+pub struct Manager {
+    marker: marker::PhantomData<()>,
+}
+
+impl Manager {
+    fn new() -> Self {
+        Manager {
+            marker: marker::PhantomData,
+        }
+    }
+
+    /// Connects to a Nitrokey device.
+    ///
+    /// This method can be used to connect to any connected device, both a Nitrokey Pro and a
+    /// Nitrokey Storage.
+    ///
+    /// # Errors
+    ///
+    /// - [`NotConnected`][] if no Nitrokey device is connected
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use nitrokey::DeviceWrapper;
+    ///
+    /// fn do_something(device: DeviceWrapper) {}
+    ///
+    /// let mut manager = nitrokey::take()?;
+    /// match manager.connect() {
+    ///     Ok(device) => do_something(device),
+    ///     Err(err) => println!("Could not connect to a Nitrokey: {}", err),
+    /// }
+    /// # Ok::<(), nitrokey::Error>(())
+    /// ```
+    ///
+    /// [`NotConnected`]: enum.CommunicationError.html#variant.NotConnected
+    pub fn connect(&mut self) -> Result<DeviceWrapper<'_>, Error> {
+        if unsafe { nitrokey_sys::NK_login_auto() } == 1 {
+            device::get_connected_device(self)
+        } else {
+            Err(CommunicationError::NotConnected.into())
+        }
+    }
+
+    /// Connects to a Nitrokey device of the given model.
+    ///
+    /// # Errors
+    ///
+    /// - [`NotConnected`][] if no Nitrokey device of the given model is connected
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use nitrokey::DeviceWrapper;
+    /// use nitrokey::Model;
+    ///
+    /// fn do_something(device: DeviceWrapper) {}
+    ///
+    /// match nitrokey::take()?.connect_model(Model::Pro) {
+    ///     Ok(device) => do_something(device),
+    ///     Err(err) => println!("Could not connect to a Nitrokey Pro: {}", err),
+    /// }
+    /// # Ok::<(), nitrokey::Error>(())
+    /// ```
+    ///
+    /// [`NotConnected`]: enum.CommunicationError.html#variant.NotConnected
+    pub fn connect_model(&mut self, model: Model) -> Result<DeviceWrapper<'_>, Error> {
+        if device::connect_enum(model) {
+            Ok(device::create_device_wrapper(self, model))
+        } else {
+            Err(CommunicationError::NotConnected.into())
+        }
+    }
+
+    /// Connects to a Nitrokey Pro.
+    ///
+    /// # Errors
+    ///
+    /// - [`NotConnected`][] if no Nitrokey device of the given model is connected
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use nitrokey::Pro;
+    ///
+    /// fn use_pro(device: Pro) {}
+    ///
+    /// match nitrokey::take()?.connect_pro() {
+    ///     Ok(device) => use_pro(device),
+    ///     Err(err) => println!("Could not connect to the Nitrokey Pro: {}", err),
+    /// }
+    /// # Ok::<(), nitrokey::Error>(())
+    /// ```
+    ///
+    /// [`NotConnected`]: enum.CommunicationError.html#variant.NotConnected
+    pub fn connect_pro(&mut self) -> Result<Pro<'_>, Error> {
+        if device::connect_enum(device::Model::Pro) {
+            Ok(device::Pro::new(self))
+        } else {
+            Err(CommunicationError::NotConnected.into())
+        }
+    }
+
+    /// Connects to a Nitrokey Storage.
+    ///
+    /// # Errors
+    ///
+    /// - [`NotConnected`][] if no Nitrokey device of the given model is connected
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use nitrokey::Storage;
+    ///
+    /// fn use_storage(device: Storage) {}
+    ///
+    /// match nitrokey::take()?.connect_storage() {
+    ///     Ok(device) => use_storage(device),
+    ///     Err(err) => println!("Could not connect to the Nitrokey Storage: {}", err),
+    /// }
+    /// # Ok::<(), nitrokey::Error>(())
+    /// ```
+    ///
+    /// [`NotConnected`]: enum.CommunicationError.html#variant.NotConnected
+    pub fn connect_storage(&mut self) -> Result<Storage<'_>, Error> {
+        if device::connect_enum(Model::Storage) {
+            Ok(Storage::new(self))
+        } else {
+            Err(CommunicationError::NotConnected.into())
+        }
+    }
+}
+
+/// Take an instance of the connection manager, blocking until an instance is available.
+///
+/// There may only be one [`Manager`][] instance at the same time.  If there already is an
+/// instance, this method blocks.  If you want a non-blocking version, use [`take`][].
+///
+/// # Errors
+///
+/// - [`PoisonError`][] if the lock is poisoned
+///
+/// [`take`]: fn.take.html
+/// [`PoisonError`]: struct.Error.html#variant.PoisonError
+/// [`Manager`]: struct.Manager.html
+pub fn take_blocking() -> Result<sync::MutexGuard<'static, Manager>, Error> {
+    MANAGER.lock().map_err(Into::into)
+}
+
+/// Try to take an instance of the connection manager.
+///
+/// There may only be one [`Manager`][] instance at the same time.  If there already is an
+/// instance, a [`ConcurrentAccessError`][] is returned.  If you want a blocking version, use
+/// [`take_blocking`][].  If you want to access the manager instance even if the cache is poisoned,
+/// use [`force_take`][].
+///
+/// # Errors
+///
+/// - [`ConcurrentAccessError`][] if the token for the `Manager` instance cannot be locked
+/// - [`PoisonError`][] if the lock is poisoned
+///
+/// [`take_blocking`]: fn.take_blocking.html
+/// [`force_take`]: fn.force_take.html
+/// [`ConcurrentAccessError`]: struct.Error.html#variant.ConcurrentAccessError
+/// [`PoisonError`]: struct.Error.html#variant.PoisonError
+/// [`Manager`]: struct.Manager.html
+pub fn take() -> Result<sync::MutexGuard<'static, Manager>, Error> {
+    MANAGER.try_lock().map_err(Into::into)
+}
+
+/// Try to take an instance of the connection manager, ignoring a poisoned cache.
+///
+/// There may only be one [`Manager`][] instance at the same time.  If there already is an
+/// instance, a [`ConcurrentAccessError`][] is returned.  If you want a blocking version, use
+/// [`take_blocking`][].
+///
+/// If a thread has previously panicked while accessing the manager instance, the cache is
+/// poisoned.  The default implementation, [`take`][], returns a [`PoisonError`][] on subsequent
+/// calls.  This implementation ignores the poisoned cache and returns the manager instance.
+///
+/// # Errors
+///
+/// - [`ConcurrentAccessError`][] if the token for the `Manager` instance cannot be locked
+///
+/// [`take`]: fn.take.html
+/// [`take_blocking`]: fn.take_blocking.html
+/// [`ConcurrentAccessError`]: struct.Error.html#variant.ConcurrentAccessError
+/// [`Manager`]: struct.Manager.html
+pub fn force_take() -> Result<sync::MutexGuard<'static, Manager>, Error> {
+    match take() {
+        Ok(guard) => Ok(guard),
+        Err(err) => match err {
+            Error::PoisonError(err) => Ok(err.into_inner()),
+            err => Err(err),
+        },
+    }
+}
+
 /// Enables or disables debug output.  Calling this method with `true` is equivalent to setting the
 /// log level to `Debug`; calling it with `false` is equivalent to the log level `Error` (see
 /// [`set_log_level`][]).
@@ -149,21 +438,28 @@ pub fn set_log_level(level: LogLevel) {
 
 /// Returns the libnitrokey library version.
 ///
+/// # Errors
+///
+/// - [`Utf8Error`][] if libnitrokey returned an invalid UTF-8 string
+///
 /// # Example
 ///
 /// ```
-/// let version = nitrokey::get_library_version();
+/// let version = nitrokey::get_library_version()?;
 /// println!("Using libnitrokey {}", version.git);
+/// # Ok::<(), nitrokey::Error>(())
 /// ```
-pub fn get_library_version() -> Version {
+///
+/// [`Utf8Error`]: enum.Error.html#variant.Utf8Error
+pub fn get_library_version() -> Result<Version, Error> {
     // NK_get_library_version returns a static string, so we don’t have to free the pointer.
     let git = unsafe { nitrokey_sys::NK_get_library_version() };
     let git = if git.is_null() {
         String::new()
     } else {
-        util::owned_str_from_ptr(git)
+        util::owned_str_from_ptr(git)?
     };
     let major = unsafe { nitrokey_sys::NK_get_major_library_version() };
     let minor = unsafe { nitrokey_sys::NK_get_minor_library_version() };
-    Version { git, major, minor }
+    Ok(Version { git, major, minor })
 }
diff --git a/src/otp.rs b/src/otp.rs
index 901bef9..4667aff 100644
--- a/src/otp.rs
+++ b/src/otp.rs
@@ -1,8 +1,12 @@
+// Copyright (C) 2018-2019 Robin Krahl <robin.krahl@ireas.org>
+// SPDX-License-Identifier: MIT
+
 use std::ffi::CString;
 
 use nitrokey_sys;
 
-use crate::util::{get_command_result, get_cstring, result_from_string, CommandError};
+use crate::error::Error;
+use crate::util::{get_command_result, get_cstring, result_from_string};
 
 /// Modes for one-time password generation.
 #[derive(Clone, Copy, Debug, PartialEq)]
@@ -28,28 +32,29 @@ pub trait ConfigureOtp {
     ///
     /// ```no_run
     /// use nitrokey::{Authenticate, ConfigureOtp, OtpMode, OtpSlotData};
-    /// # use nitrokey::CommandError;
+    /// # use nitrokey::Error;
     ///
-    /// # fn try_main() -> Result<(), (CommandError)> {
-    /// let device = nitrokey::connect()?;
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let device = manager.connect()?;
     /// let slot_data = OtpSlotData::new(1, "test", "01234567890123456689", OtpMode::SixDigits);
     /// match device.authenticate_admin("12345678") {
-    ///     Ok(admin) => {
+    ///     Ok(mut admin) => {
     ///         match admin.write_hotp_slot(slot_data, 0) {
     ///             Ok(()) => println!("Successfully wrote slot."),
-    ///             Err(err) => println!("Could not write slot: {}", err),
+    ///             Err(err) => eprintln!("Could not write slot: {}", err),
     ///         }
     ///     },
-    ///     Err((_, err)) => println!("Could not authenticate as admin: {}", err),
+    ///     Err((_, err)) => eprintln!("Could not authenticate as admin: {}", err),
     /// }
     /// #     Ok(())
     /// # }
     /// ```
     ///
-    /// [`InvalidSlot`]: enum.CommandError.html#variant.InvalidSlot
-    /// [`InvalidString`]: enum.CommandError.html#variant.InvalidString
+    /// [`InvalidSlot`]: enum.LibraryError.html#variant.InvalidSlot
+    /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     /// [`NoName`]: enum.CommandError.html#variant.NoName
-    fn write_hotp_slot(&self, data: OtpSlotData, counter: u64) -> Result<(), CommandError>;
+    fn write_hotp_slot(&mut self, data: OtpSlotData, counter: u64) -> Result<(), Error>;
 
     /// Configure a TOTP slot with the given data and set the TOTP time window to the given value
     /// (default 30).
@@ -64,28 +69,29 @@ pub trait ConfigureOtp {
     ///
     /// ```no_run
     /// use nitrokey::{Authenticate, ConfigureOtp, OtpMode, OtpSlotData};
-    /// # use nitrokey::CommandError;
+    /// # use nitrokey::Error;
     ///
-    /// # fn try_main() -> Result<(), (CommandError)> {
-    /// let device = nitrokey::connect()?;
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let device = manager.connect()?;
     /// let slot_data = OtpSlotData::new(1, "test", "01234567890123456689", OtpMode::EightDigits);
     /// match device.authenticate_admin("12345678") {
-    ///     Ok(admin) => {
+    ///     Ok(mut admin) => {
     ///         match admin.write_totp_slot(slot_data, 30) {
     ///             Ok(()) => println!("Successfully wrote slot."),
-    ///             Err(err) => println!("Could not write slot: {}", err),
+    ///             Err(err) => eprintln!("Could not write slot: {}", err),
     ///         }
     ///     },
-    ///     Err((_, err)) => println!("Could not authenticate as admin: {}", err),
+    ///     Err((_, err)) => eprintln!("Could not authenticate as admin: {}", err),
     /// }
     /// #     Ok(())
     /// # }
     /// ```
     ///
-    /// [`InvalidSlot`]: enum.CommandError.html#variant.InvalidSlot
-    /// [`InvalidString`]: enum.CommandError.html#variant.InvalidString
+    /// [`InvalidSlot`]: enum.LibraryError.html#variant.InvalidSlot
+    /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     /// [`NoName`]: enum.CommandError.html#variant.NoName
-    fn write_totp_slot(&self, data: OtpSlotData, time_window: u16) -> Result<(), CommandError>;
+    fn write_totp_slot(&mut self, data: OtpSlotData, time_window: u16) -> Result<(), Error>;
 
     /// Erases an HOTP slot.
     ///
@@ -97,25 +103,26 @@ pub trait ConfigureOtp {
     ///
     /// ```no_run
     /// use nitrokey::{Authenticate, ConfigureOtp};
-    /// # use nitrokey::CommandError;
+    /// # use nitrokey::Error;
     ///
-    /// # fn try_main() -> Result<(), (CommandError)> {
-    /// let device = nitrokey::connect()?;
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let device = manager.connect()?;
     /// match device.authenticate_admin("12345678") {
-    ///     Ok(admin) => {
+    ///     Ok(mut admin) => {
     ///         match admin.erase_hotp_slot(1) {
     ///             Ok(()) => println!("Successfully erased slot."),
-    ///             Err(err) => println!("Could not erase slot: {}", err),
+    ///             Err(err) => eprintln!("Could not erase slot: {}", err),
     ///         }
     ///     },
-    ///     Err((_, err)) => println!("Could not authenticate as admin: {}", err),
+    ///     Err((_, err)) => eprintln!("Could not authenticate as admin: {}", err),
     /// }
     /// #     Ok(())
     /// # }
     /// ```
     ///
-    /// [`InvalidSlot`]: enum.CommandError.html#variant.InvalidSlot
-    fn erase_hotp_slot(&self, slot: u8) -> Result<(), CommandError>;
+    /// [`InvalidSlot`]: enum.LibraryError.html#variant.InvalidSlot
+    fn erase_hotp_slot(&mut self, slot: u8) -> Result<(), Error>;
 
     /// Erases a TOTP slot.
     ///
@@ -127,25 +134,26 @@ pub trait ConfigureOtp {
     ///
     /// ```no_run
     /// use nitrokey::{Authenticate, ConfigureOtp};
-    /// # use nitrokey::CommandError;
+    /// # use nitrokey::Error;
     ///
-    /// # fn try_main() -> Result<(), (CommandError)> {
-    /// let device = nitrokey::connect()?;
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let device = manager.connect()?;
     /// match device.authenticate_admin("12345678") {
-    ///     Ok(admin) => {
+    ///     Ok(mut admin) => {
     ///         match admin.erase_totp_slot(1) {
     ///             Ok(()) => println!("Successfully erased slot."),
-    ///             Err(err) => println!("Could not erase slot: {}", err),
+    ///             Err(err) => eprintln!("Could not erase slot: {}", err),
     ///         }
     ///     },
-    ///     Err((_, err)) => println!("Could not authenticate as admin: {}", err),
+    ///     Err((_, err)) => eprintln!("Could not authenticate as admin: {}", err),
     /// }
     /// #     Ok(())
     /// # }
     /// ```
     ///
-    /// [`InvalidSlot`]: enum.CommandError.html#variant.InvalidSlot
-    fn erase_totp_slot(&self, slot: u8) -> Result<(), CommandError>;
+    /// [`InvalidSlot`]: enum.LibraryError.html#variant.InvalidSlot
+    fn erase_totp_slot(&mut self, slot: u8) -> Result<(), Error>;
 }
 
 /// Provides methods to generate OTP codes and to query OTP slots on a Nitrokey
@@ -164,14 +172,15 @@ pub trait GenerateOtp {
     /// ```no_run
     /// use std::time;
     /// use nitrokey::GenerateOtp;
-    /// # use nitrokey::CommandError;
+    /// # use nitrokey::Error;
     ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let mut device = manager.connect()?;
     /// let time = time::SystemTime::now().duration_since(time::UNIX_EPOCH);
     /// match time {
     ///     Ok(time) => device.set_time(time.as_secs(), false)?,
-    ///     Err(_) => println!("The system time is before the Unix epoch!"),
+    ///     Err(_) => eprintln!("The system time is before the Unix epoch!"),
     /// }
     /// #     Ok(())
     /// # }
@@ -183,7 +192,7 @@ pub trait GenerateOtp {
     ///
     /// [`get_totp_code`]: #method.get_totp_code
     /// [`Timestamp`]: enum.CommandError.html#variant.Timestamp
-    fn set_time(&self, time: u64, force: bool) -> Result<(), CommandError> {
+    fn set_time(&mut self, time: u64, force: bool) -> Result<(), Error> {
         let result = if force {
             unsafe { nitrokey_sys::NK_totp_set_time(time) }
         } else {
@@ -202,23 +211,24 @@ pub trait GenerateOtp {
     /// # Example
     ///
     /// ```no_run
-    /// use nitrokey::{CommandError, GenerateOtp};
+    /// use nitrokey::{CommandError, Error, GenerateOtp};
     ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let device = manager.connect()?;
     /// match device.get_hotp_slot_name(1) {
     ///     Ok(name) => println!("HOTP slot 1: {}", name),
-    ///     Err(CommandError::SlotNotProgrammed) => println!("HOTP slot 1 not programmed"),
-    ///     Err(err) => println!("Could not get slot name: {}", err),
+    ///     Err(Error::CommandError(CommandError::SlotNotProgrammed)) => eprintln!("HOTP slot 1 not programmed"),
+    ///     Err(err) => eprintln!("Could not get slot name: {}", err),
     /// };
     /// #     Ok(())
     /// # }
     /// ```
     ///
-    /// [`InvalidSlot`]: enum.CommandError.html#variant.InvalidSlot
+    /// [`InvalidSlot`]: enum.LibraryError.html#variant.InvalidSlot
     /// [`SlotNotProgrammed`]: enum.CommandError.html#variant.SlotNotProgrammed
-    fn get_hotp_slot_name(&self, slot: u8) -> Result<String, CommandError> {
-        unsafe { result_from_string(nitrokey_sys::NK_get_hotp_slot_name(slot)) }
+    fn get_hotp_slot_name(&self, slot: u8) -> Result<String, Error> {
+        result_from_string(unsafe { nitrokey_sys::NK_get_hotp_slot_name(slot) })
     }
 
     /// Returns the name of the given TOTP slot.
@@ -231,23 +241,24 @@ pub trait GenerateOtp {
     /// # Example
     ///
     /// ```no_run
-    /// use nitrokey::{CommandError, GenerateOtp};
+    /// use nitrokey::{CommandError, Error, GenerateOtp};
     ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let device = manager.connect()?;
     /// match device.get_totp_slot_name(1) {
     ///     Ok(name) => println!("TOTP slot 1: {}", name),
-    ///     Err(CommandError::SlotNotProgrammed) => println!("TOTP slot 1 not programmed"),
-    ///     Err(err) => println!("Could not get slot name: {}", err),
+    ///     Err(Error::CommandError(CommandError::SlotNotProgrammed)) => eprintln!("TOTP slot 1 not programmed"),
+    ///     Err(err) => eprintln!("Could not get slot name: {}", err),
     /// };
     /// #     Ok(())
     /// # }
     /// ```
     ///
-    /// [`InvalidSlot`]: enum.CommandError.html#variant.InvalidSlot
+    /// [`InvalidSlot`]: enum.LibraryError.html#variant.InvalidSlot
     /// [`SlotNotProgrammed`]: enum.CommandError.html#variant.SlotNotProgrammed
-    fn get_totp_slot_name(&self, slot: u8) -> Result<String, CommandError> {
-        unsafe { result_from_string(nitrokey_sys::NK_get_totp_slot_name(slot)) }
+    fn get_totp_slot_name(&self, slot: u8) -> Result<String, Error> {
+        result_from_string(unsafe { nitrokey_sys::NK_get_totp_slot_name(slot) })
     }
 
     /// Generates an HOTP code on the given slot.  This operation may require user authorization,
@@ -263,10 +274,11 @@ pub trait GenerateOtp {
     ///
     /// ```no_run
     /// use nitrokey::GenerateOtp;
-    /// # use nitrokey::CommandError;
+    /// # use nitrokey::Error;
     ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let mut device = manager.connect()?;
     /// let code = device.get_hotp_code(1)?;
     /// println!("Generated HOTP code on slot 1: {}", code);
     /// #     Ok(())
@@ -274,13 +286,11 @@ pub trait GenerateOtp {
     /// ```
     ///
     /// [`get_config`]: trait.Device.html#method.get_config
-    /// [`InvalidSlot`]: enum.CommandError.html#variant.InvalidSlot
+    /// [`InvalidSlot`]: enum.LibraryError.html#variant.InvalidSlot
     /// [`NotAuthorized`]: enum.CommandError.html#variant.NotAuthorized
     /// [`SlotNotProgrammed`]: enum.CommandError.html#variant.SlotNotProgrammed
-    fn get_hotp_code(&self, slot: u8) -> Result<String, CommandError> {
-        unsafe {
-            return result_from_string(nitrokey_sys::NK_get_hotp_code(slot));
-        }
+    fn get_hotp_code(&mut self, slot: u8) -> Result<String, Error> {
+        result_from_string(unsafe { nitrokey_sys::NK_get_hotp_code(slot) })
     }
 
     /// Generates a TOTP code on the given slot.  This operation may require user authorization,
@@ -300,10 +310,11 @@ pub trait GenerateOtp {
     /// ```no_run
     /// use std::time;
     /// use nitrokey::GenerateOtp;
-    /// # use nitrokey::CommandError;
+    /// # use nitrokey::Error;
     ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let mut device = manager.connect()?;
     /// let time = time::SystemTime::now().duration_since(time::UNIX_EPOCH);
     /// match time {
     ///     Ok(time) => {
@@ -311,7 +322,7 @@ pub trait GenerateOtp {
     ///         let code = device.get_totp_code(1)?;
     ///         println!("Generated TOTP code on slot 1: {}", code);
     ///     },
-    ///     Err(_) => println!("Timestamps before 1970-01-01 are not supported!"),
+    ///     Err(_) => eprintln!("Timestamps before 1970-01-01 are not supported!"),
     /// }
     /// #     Ok(())
     /// # }
@@ -319,13 +330,11 @@ pub trait GenerateOtp {
     ///
     /// [`set_time`]: #method.set_time
     /// [`get_config`]: trait.Device.html#method.get_config
-    /// [`InvalidSlot`]: enum.CommandError.html#variant.InvalidSlot
+    /// [`InvalidSlot`]: enum.LibraryError.html#variant.InvalidSlot
     /// [`NotAuthorized`]: enum.CommandError.html#variant.NotAuthorized
     /// [`SlotNotProgrammed`]: enum.CommandError.html#variant.SlotNotProgrammed
-    fn get_totp_code(&self, slot: u8) -> Result<String, CommandError> {
-        unsafe {
-            return result_from_string(nitrokey_sys::NK_get_totp_code(slot, 0, 0, 0));
-        }
+    fn get_totp_code(&self, slot: u8) -> Result<String, Error> {
+        result_from_string(unsafe { nitrokey_sys::NK_get_totp_code(slot, 0, 0, 0) })
     }
 }
 
@@ -395,7 +404,7 @@ impl OtpSlotData {
 }
 
 impl RawOtpSlotData {
-    pub fn new(data: OtpSlotData) -> Result<RawOtpSlotData, CommandError> {
+    pub fn new(data: OtpSlotData) -> Result<RawOtpSlotData, Error> {
         let name = get_cstring(data.name)?;
         let secret = get_cstring(data.secret)?;
         let use_token_id = data.token_id.is_some();
diff --git a/src/pws.rs b/src/pws.rs
index 28f0681..3398deb 100644
--- a/src/pws.rs
+++ b/src/pws.rs
@@ -1,10 +1,12 @@
+// Copyright (C) 2018-2019 Robin Krahl <robin.krahl@ireas.org>
+// SPDX-License-Identifier: MIT
+
 use libc;
 use nitrokey_sys;
 
 use crate::device::{Device, DeviceWrapper, Pro, Storage};
-use crate::util::{
-    get_command_result, get_cstring, get_last_error, result_from_string, CommandError,
-};
+use crate::error::{CommandError, Error};
+use crate::util::{get_command_result, get_cstring, get_last_error, result_from_string};
 
 /// The number of slots in a [`PasswordSafe`][].
 ///
@@ -30,9 +32,9 @@ pub const SLOT_COUNT: u8 = 16;
 ///
 /// ```no_run
 /// use nitrokey::{Device, GetPasswordSafe, PasswordSafe};
-/// # use nitrokey::CommandError;
+/// # use nitrokey::Error;
 ///
-/// fn use_password_safe(pws: &PasswordSafe) -> Result<(), CommandError> {
+/// fn use_password_safe(pws: &PasswordSafe) -> Result<(), Error> {
 ///     let name = pws.get_slot_name(0)?;
 ///     let login = pws.get_slot_login(0)?;
 ///     let password = pws.get_slot_login(0)?;
@@ -40,10 +42,12 @@ pub const SLOT_COUNT: u8 = 16;
 ///     Ok(())
 /// }
 ///
-/// # fn try_main() -> Result<(), CommandError> {
-/// let device = nitrokey::connect()?;
+/// # fn try_main() -> Result<(), Error> {
+/// let mut manager = nitrokey::take()?;
+/// let mut device = manager.connect()?;
 /// let pws = device.get_password_safe("123456")?;
 /// use_password_safe(&pws);
+/// drop(pws);
 /// device.lock()?;
 /// #     Ok(())
 /// # }
@@ -53,8 +57,9 @@ pub const SLOT_COUNT: u8 = 16;
 /// [`get_password_safe`]: trait.GetPasswordSafe.html#method.get_password_safe
 /// [`lock`]: trait.Device.html#method.lock
 /// [`GetPasswordSafe`]: trait.GetPasswordSafe.html
-pub struct PasswordSafe<'a> {
-    _device: &'a dyn Device,
+#[derive(Debug)]
+pub struct PasswordSafe<'a, 'b> {
+    _device: &'a dyn Device<'b>,
 }
 
 /// Provides access to a [`PasswordSafe`][].
@@ -63,7 +68,7 @@ pub struct PasswordSafe<'a> {
 /// retrieved from it.
 ///
 /// [`PasswordSafe`]: struct.PasswordSafe.html
-pub trait GetPasswordSafe {
+pub trait GetPasswordSafe<'a> {
     /// Enables and returns the password safe.
     ///
     /// The underlying device must always live at least as long as a password safe retrieved from
@@ -89,19 +94,20 @@ pub trait GetPasswordSafe {
     ///
     /// ```no_run
     /// use nitrokey::{Device, GetPasswordSafe, PasswordSafe};
-    /// # use nitrokey::CommandError;
+    /// # use nitrokey::Error;
     ///
     /// fn use_password_safe(pws: &PasswordSafe) {}
     ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let mut device = manager.connect()?;
     /// match device.get_password_safe("123456") {
     ///     Ok(pws) => {
     ///         use_password_safe(&pws);
-    ///         device.lock()?;
     ///     },
-    ///     Err(err) => println!("Could not open the password safe: {}", err),
+    ///     Err(err) => eprintln!("Could not open the password safe: {}", err),
     /// };
+    /// device.lock()?;
     /// #     Ok(())
     /// # }
     /// ```
@@ -110,34 +116,30 @@ pub trait GetPasswordSafe {
     /// [`lock`]: trait.Device.html#method.lock
     /// [`AesDecryptionFailed`]: enum.CommandError.html#variant.AesDecryptionFailed
     /// [`Device::build_aes_key`]: trait.Device.html#method.build_aes_key
-    /// [`InvalidString`]: enum.CommandError.html#variant.InvalidString
+    /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     /// [`Unknown`]: enum.CommandError.html#variant.Unknown
     /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    fn get_password_safe(&self, user_pin: &str) -> Result<PasswordSafe<'_>, CommandError>;
+    fn get_password_safe(&mut self, user_pin: &str) -> Result<PasswordSafe<'_, 'a>, Error>;
 }
 
-fn get_password_safe<'a>(
-    device: &'a dyn Device,
+fn get_password_safe<'a, 'b>(
+    device: &'a dyn Device<'b>,
     user_pin: &str,
-) -> Result<PasswordSafe<'a>, CommandError> {
+) -> Result<PasswordSafe<'a, 'b>, Error> {
     let user_pin_string = get_cstring(user_pin)?;
-    let result = unsafe {
-        get_command_result(nitrokey_sys::NK_enable_password_safe(
-            user_pin_string.as_ptr(),
-        ))
-    };
-    result.map(|()| PasswordSafe { _device: device })
+    get_command_result(unsafe { nitrokey_sys::NK_enable_password_safe(user_pin_string.as_ptr()) })
+        .map(|_| PasswordSafe { _device: device })
 }
 
-fn get_pws_result(s: String) -> Result<String, CommandError> {
+fn get_pws_result(s: String) -> Result<String, Error> {
     if s.is_empty() {
-        Err(CommandError::SlotNotProgrammed)
+        Err(CommandError::SlotNotProgrammed.into())
     } else {
         Ok(s)
     }
 }
 
-impl<'a> PasswordSafe<'a> {
+impl<'a, 'b> PasswordSafe<'a, 'b> {
     /// Returns the status of all password slots.
     ///
     /// The status indicates whether a slot is programmed or not.
@@ -146,10 +148,11 @@ impl<'a> PasswordSafe<'a> {
     ///
     /// ```no_run
     /// use nitrokey::{GetPasswordSafe, SLOT_COUNT};
-    /// # use nitrokey::CommandError;
+    /// # use nitrokey::Error;
     ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let mut device = manager.connect()?;
     /// let pws = device.get_password_safe("123456")?;
     /// pws.get_slot_status()?.iter().enumerate().for_each(|(slot, programmed)| {
     ///     let status = match *programmed {
@@ -161,7 +164,7 @@ impl<'a> PasswordSafe<'a> {
     /// #     Ok(())
     /// # }
     /// ```
-    pub fn get_slot_status(&self) -> Result<[bool; SLOT_COUNT as usize], CommandError> {
+    pub fn get_slot_status(&self) -> Result<[bool; SLOT_COUNT as usize], Error> {
         let status_ptr = unsafe { nitrokey_sys::NK_get_password_safe_slot_status() };
         if status_ptr.is_null() {
             return Err(get_last_error());
@@ -191,10 +194,11 @@ impl<'a> PasswordSafe<'a> {
     ///
     /// ```no_run
     /// use nitrokey::GetPasswordSafe;
-    /// # use nitrokey::CommandError;
+    /// # use nitrokey::Error;
     ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let mut device = manager.connect()?;
     /// match device.get_password_safe("123456") {
     ///     Ok(pws) => {
     ///         let name = pws.get_slot_name(0)?;
@@ -202,16 +206,16 @@ impl<'a> PasswordSafe<'a> {
     ///         let password = pws.get_slot_login(0)?;
     ///         println!("Credentials for {}: login {}, password {}", name, login, password);
     ///     },
-    ///     Err(err) => println!("Could not open the password safe: {}", err),
+    ///     Err(err) => eprintln!("Could not open the password safe: {}", err),
     /// };
     /// #     Ok(())
     /// # }
     /// ```
     ///
-    /// [`InvalidSlot`]: enum.CommandError.html#variant.InvalidSlot
+    /// [`InvalidSlot`]: enum.LibraryError.html#variant.InvalidSlot
     /// [`SlotNotProgrammed`]: enum.CommandError.html#variant.SlotNotProgrammed
-    pub fn get_slot_name(&self, slot: u8) -> Result<String, CommandError> {
-        unsafe { result_from_string(nitrokey_sys::NK_get_password_safe_slot_name(slot)) }
+    pub fn get_slot_name(&self, slot: u8) -> Result<String, Error> {
+        result_from_string(unsafe { nitrokey_sys::NK_get_password_safe_slot_name(slot) })
             .and_then(get_pws_result)
     }
 
@@ -228,10 +232,11 @@ impl<'a> PasswordSafe<'a> {
     ///
     /// ```no_run
     /// use nitrokey::GetPasswordSafe;
-    /// # use nitrokey::CommandError;
+    /// # use nitrokey::Error;
     ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let mut device = manager.connect()?;
     /// let pws = device.get_password_safe("123456")?;
     /// let name = pws.get_slot_name(0)?;
     /// let login = pws.get_slot_login(0)?;
@@ -241,10 +246,10 @@ impl<'a> PasswordSafe<'a> {
     /// # }
     /// ```
     ///
-    /// [`InvalidSlot`]: enum.CommandError.html#variant.InvalidSlot
+    /// [`InvalidSlot`]: enum.LibraryError.html#variant.InvalidSlot
     /// [`SlotNotProgrammed`]: enum.CommandError.html#variant.SlotNotProgrammed
-    pub fn get_slot_login(&self, slot: u8) -> Result<String, CommandError> {
-        unsafe { result_from_string(nitrokey_sys::NK_get_password_safe_slot_login(slot)) }
+    pub fn get_slot_login(&self, slot: u8) -> Result<String, Error> {
+        result_from_string(unsafe { nitrokey_sys::NK_get_password_safe_slot_login(slot) })
             .and_then(get_pws_result)
     }
 
@@ -261,10 +266,11 @@ impl<'a> PasswordSafe<'a> {
     ///
     /// ```no_run
     /// use nitrokey::GetPasswordSafe;
-    /// # use nitrokey::CommandError;
+    /// # use nitrokey::Error;
     ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let mut device = manager.connect()?;
     /// let pws = device.get_password_safe("123456")?;
     /// let name = pws.get_slot_name(0)?;
     /// let login = pws.get_slot_login(0)?;
@@ -274,10 +280,10 @@ impl<'a> PasswordSafe<'a> {
     /// # }
     /// ```
     ///
-    /// [`InvalidSlot`]: enum.CommandError.html#variant.InvalidSlot
+    /// [`InvalidSlot`]: enum.LibraryError.html#variant.InvalidSlot
     /// [`SlotNotProgrammed`]: enum.CommandError.html#variant.SlotNotProgrammed
-    pub fn get_slot_password(&self, slot: u8) -> Result<String, CommandError> {
-        unsafe { result_from_string(nitrokey_sys::NK_get_password_safe_slot_password(slot)) }
+    pub fn get_slot_password(&self, slot: u8) -> Result<String, Error> {
+        result_from_string(unsafe { nitrokey_sys::NK_get_password_safe_slot_password(slot) })
             .and_then(get_pws_result)
     }
 
@@ -292,10 +298,11 @@ impl<'a> PasswordSafe<'a> {
     ///
     /// ```no_run
     /// use nitrokey::GetPasswordSafe;
-    /// # use nitrokey::CommandError;
+    /// # use nitrokey::Error;
     ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let mut device = manager.connect()?;
     /// let pws = device.get_password_safe("123456")?;
     /// let name = pws.get_slot_name(0)?;
     /// let login = pws.get_slot_login(0)?;
@@ -305,26 +312,26 @@ impl<'a> PasswordSafe<'a> {
     /// # }
     /// ```
     ///
-    /// [`InvalidSlot`]: enum.CommandError.html#variant.InvalidSlot
-    /// [`InvalidString`]: enum.CommandError.html#variant.InvalidString
+    /// [`InvalidSlot`]: enum.LibraryError.html#variant.InvalidSlot
+    /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     pub fn write_slot(
-        &self,
+        &mut self,
         slot: u8,
         name: &str,
         login: &str,
         password: &str,
-    ) -> Result<(), CommandError> {
+    ) -> Result<(), Error> {
         let name_string = get_cstring(name)?;
         let login_string = get_cstring(login)?;
         let password_string = get_cstring(password)?;
-        unsafe {
-            get_command_result(nitrokey_sys::NK_write_password_safe_slot(
+        get_command_result(unsafe {
+            nitrokey_sys::NK_write_password_safe_slot(
                 slot,
                 name_string.as_ptr(),
                 login_string.as_ptr(),
                 password_string.as_ptr(),
-            ))
-        }
+            )
+        })
     }
 
     /// Erases the given slot.  Erasing clears the stored name, login and password (if the slot was
@@ -338,46 +345,47 @@ impl<'a> PasswordSafe<'a> {
     ///
     /// ```no_run
     /// use nitrokey::GetPasswordSafe;
-    /// # use nitrokey::CommandError;
+    /// # use nitrokey::Error;
     ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
-    /// let pws = device.get_password_safe("123456")?;
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut manager = nitrokey::take()?;
+    /// let mut device = manager.connect()?;
+    /// let mut pws = device.get_password_safe("123456")?;
     /// match pws.erase_slot(0) {
     ///     Ok(()) => println!("Erased slot 0."),
-    ///     Err(err) => println!("Could not erase slot 0: {}", err),
+    ///     Err(err) => eprintln!("Could not erase slot 0: {}", err),
     /// };
     /// #     Ok(())
     /// # }
     /// ```
     ///
-    /// [`InvalidSlot`]: enum.CommandError.html#variant.InvalidSlot
-    pub fn erase_slot(&self, slot: u8) -> Result<(), CommandError> {
-        unsafe { get_command_result(nitrokey_sys::NK_erase_password_safe_slot(slot)) }
+    /// [`InvalidSlot`]: enum.LibraryError.html#variant.InvalidSlot
+    pub fn erase_slot(&mut self, slot: u8) -> Result<(), Error> {
+        get_command_result(unsafe { nitrokey_sys::NK_erase_password_safe_slot(slot) })
     }
 }
 
-impl<'a> Drop for PasswordSafe<'a> {
+impl<'a, 'b> Drop for PasswordSafe<'a, 'b> {
     fn drop(&mut self) {
         // TODO: disable the password safe -- NK_lock_device has side effects on the Nitrokey
         // Storage, see https://github.com/Nitrokey/nitrokey-storage-firmware/issues/65
     }
 }
 
-impl GetPasswordSafe for Pro {
-    fn get_password_safe(&self, user_pin: &str) -> Result<PasswordSafe<'_>, CommandError> {
+impl<'a> GetPasswordSafe<'a> for Pro<'a> {
+    fn get_password_safe(&mut self, user_pin: &str) -> Result<PasswordSafe<'_, 'a>, Error> {
         get_password_safe(self, user_pin)
     }
 }
 
-impl GetPasswordSafe for Storage {
-    fn get_password_safe(&self, user_pin: &str) -> Result<PasswordSafe<'_>, CommandError> {
+impl<'a> GetPasswordSafe<'a> for Storage<'a> {
+    fn get_password_safe(&mut self, user_pin: &str) -> Result<PasswordSafe<'_, 'a>, Error> {
         get_password_safe(self, user_pin)
     }
 }
 
-impl GetPasswordSafe for DeviceWrapper {
-    fn get_password_safe(&self, user_pin: &str) -> Result<PasswordSafe<'_>, CommandError> {
+impl<'a> GetPasswordSafe<'a> for DeviceWrapper<'a> {
+    fn get_password_safe(&mut self, user_pin: &str) -> Result<PasswordSafe<'_, 'a>, Error> {
         get_password_safe(self, user_pin)
     }
 }
diff --git a/src/util.rs b/src/util.rs
index 567c478..5a56c55 100644
--- a/src/util.rs
+++ b/src/util.rs
@@ -1,53 +1,13 @@
-use std::borrow;
+// Copyright (C) 2018-2019 Robin Krahl <robin.krahl@ireas.org>
+// SPDX-License-Identifier: MIT
+
 use std::ffi::{CStr, CString};
-use std::fmt;
 use std::os::raw::{c_char, c_int};
 
 use libc::{c_void, free};
-use rand_core::RngCore;
-use rand_os::OsRng;
+use rand_core::{OsRng, RngCore};
 
-/// Error types returned by Nitrokey device or by the library.
-#[derive(Clone, Copy, Debug, PartialEq)]
-pub enum CommandError {
-    /// A packet with a wrong checksum has been sent or received.
-    WrongCrc,
-    /// A command tried to access an OTP slot that does not exist.
-    WrongSlot,
-    /// A command tried to generate an OTP on a slot that is not configured.
-    SlotNotProgrammed,
-    /// The provided password is wrong.
-    WrongPassword,
-    /// You are not authorized for this command or provided a wrong temporary
-    /// password.
-    NotAuthorized,
-    /// An error occurred when getting or setting the time.
-    Timestamp,
-    /// You did not provide a name for the OTP slot.
-    NoName,
-    /// This command is not supported by this device.
-    NotSupported,
-    /// This command is unknown.
-    UnknownCommand,
-    /// AES decryption failed.
-    AesDecryptionFailed,
-    /// An unknown error occurred.
-    Unknown(i64),
-    /// An unspecified error occurred.
-    Undefined,
-    /// You passed a string containing a null byte.
-    InvalidString,
-    /// A supplied string exceeded a length limit.
-    StringTooLong,
-    /// You passed an invalid slot.
-    InvalidSlot,
-    /// The supplied string was not in hexadecimal format.
-    InvalidHexString,
-    /// The target buffer was smaller than the source.
-    TargetBufferTooSmall,
-    /// An error occurred during random number generation.
-    RngError,
-}
+use crate::error::{Error, LibraryError};
 
 /// Log level for libnitrokey.
 ///
@@ -70,126 +30,59 @@ pub enum LogLevel {
     DebugL2,
 }
 
-pub fn owned_str_from_ptr(ptr: *const c_char) -> String {
-    unsafe {
-        return CStr::from_ptr(ptr).to_string_lossy().into_owned();
-    }
+pub fn owned_str_from_ptr(ptr: *const c_char) -> Result<String, Error> {
+    unsafe { CStr::from_ptr(ptr) }
+        .to_str()
+        .map(String::from)
+        .map_err(Error::from)
 }
 
-pub fn result_from_string(ptr: *const c_char) -> Result<String, CommandError> {
+pub fn result_from_string(ptr: *const c_char) -> Result<String, Error> {
     if ptr.is_null() {
-        return Err(CommandError::Undefined);
+        return Err(Error::UnexpectedError);
     }
-    unsafe {
-        let s = owned_str_from_ptr(ptr);
-        free(ptr as *mut c_void);
-        // An empty string can both indicate an error or be a valid return value.  In this case, we
-        // have to check the last command status to decide what to return.
-        if s.is_empty() {
-            get_last_result().map(|_| s)
-        } else {
-            Ok(s)
-        }
+    let s = owned_str_from_ptr(ptr)?;
+    unsafe { free(ptr as *mut c_void) };
+    // An empty string can both indicate an error or be a valid return value.  In this case, we
+    // have to check the last command status to decide what to return.
+    if s.is_empty() {
+        get_last_result().map(|_| s)
+    } else {
+        Ok(s)
     }
 }
 
-pub fn get_command_result(value: c_int) -> Result<(), CommandError> {
-    match value {
-        0 => Ok(()),
-        other => Err(CommandError::from(other)),
+pub fn result_or_error<T>(value: T) -> Result<T, Error> {
+    get_last_result().and(Ok(value))
+}
+
+pub fn get_command_result(value: c_int) -> Result<(), Error> {
+    if value == 0 {
+        Ok(())
+    } else {
+        Err(Error::from(value))
     }
 }
 
-pub fn get_last_result() -> Result<(), CommandError> {
-    let value = unsafe { nitrokey_sys::NK_get_last_command_status() } as c_int;
-    get_command_result(value)
+pub fn get_last_result() -> Result<(), Error> {
+    get_command_result(unsafe { nitrokey_sys::NK_get_last_command_status() }.into())
 }
 
-pub fn get_last_error() -> CommandError {
-    return match get_last_result() {
-        Ok(()) => CommandError::Undefined,
+pub fn get_last_error() -> Error {
+    match get_last_result() {
+        Ok(()) => Error::UnexpectedError,
         Err(err) => err,
-    };
+    }
 }
 
-pub fn generate_password(length: usize) -> Result<Vec<u8>, CommandError> {
-    let mut rng = OsRng::new()?;
+pub fn generate_password(length: usize) -> Result<Vec<u8>, Error> {
     let mut data = vec![0u8; length];
-    rng.fill_bytes(&mut data[..]);
+    OsRng.fill_bytes(&mut data[..]);
     Ok(data)
 }
 
-pub fn get_cstring<T: Into<Vec<u8>>>(s: T) -> Result<CString, CommandError> {
-    CString::new(s).or(Err(CommandError::InvalidString))
-}
-
-impl CommandError {
-    fn as_str(&self) -> borrow::Cow<'static, str> {
-        match *self {
-            CommandError::WrongCrc => {
-                "A packet with a wrong checksum has been sent or received".into()
-            }
-            CommandError::WrongSlot => "The given OTP slot does not exist".into(),
-            CommandError::SlotNotProgrammed => "The given OTP slot is not programmed".into(),
-            CommandError::WrongPassword => "The given password is wrong".into(),
-            CommandError::NotAuthorized => {
-                "You are not authorized for this command or provided a wrong temporary \
-                 password"
-                    .into()
-            }
-            CommandError::Timestamp => "An error occurred when getting or setting the time".into(),
-            CommandError::NoName => "You did not provide a name for the OTP slot".into(),
-            CommandError::NotSupported => "This command is not supported by this device".into(),
-            CommandError::UnknownCommand => "This command is unknown".into(),
-            CommandError::AesDecryptionFailed => "AES decryption failed".into(),
-            CommandError::Unknown(x) => {
-                borrow::Cow::from(format!("An unknown error occurred ({})", x))
-            }
-            CommandError::Undefined => "An unspecified error occurred".into(),
-            CommandError::InvalidString => "You passed a string containing a null byte".into(),
-            CommandError::StringTooLong => "The supplied string is too long".into(),
-            CommandError::InvalidSlot => "The given slot is invalid".into(),
-            CommandError::InvalidHexString => {
-                "The supplied string is not in hexadecimal format".into()
-            }
-            CommandError::TargetBufferTooSmall => "The target buffer is too small".into(),
-            CommandError::RngError => "An error occurred during random number generation".into(),
-        }
-    }
-}
-
-impl fmt::Display for CommandError {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "{}", self.as_str())
-    }
-}
-
-impl From<c_int> for CommandError {
-    fn from(value: c_int) -> Self {
-        match value {
-            1 => CommandError::WrongCrc,
-            2 => CommandError::WrongSlot,
-            3 => CommandError::SlotNotProgrammed,
-            4 => CommandError::WrongPassword,
-            5 => CommandError::NotAuthorized,
-            6 => CommandError::Timestamp,
-            7 => CommandError::NoName,
-            8 => CommandError::NotSupported,
-            9 => CommandError::UnknownCommand,
-            10 => CommandError::AesDecryptionFailed,
-            200 => CommandError::StringTooLong,
-            201 => CommandError::InvalidSlot,
-            202 => CommandError::InvalidHexString,
-            203 => CommandError::TargetBufferTooSmall,
-            x => CommandError::Unknown(x.into()),
-        }
-    }
-}
-
-impl From<rand_core::Error> for CommandError {
-    fn from(_error: rand_core::Error) -> Self {
-        CommandError::RngError
-    }
+pub fn get_cstring<T: Into<Vec<u8>>>(s: T) -> Result<CString, Error> {
+    CString::new(s).or_else(|_| Err(LibraryError::InvalidString.into()))
 }
 
 impl Into<i32> for LogLevel {
diff --git a/tests/device.rs b/tests/device.rs
index 849d2ff..e367558 100644
--- a/tests/device.rs
+++ b/tests/device.rs
@@ -1,3 +1,6 @@
+// Copyright (C) 2018-2019 Robin Krahl <robin.krahl@ireas.org>
+// SPDX-License-Identifier: MIT
+
 mod util;
 
 use std::ffi::CStr;
@@ -5,13 +8,12 @@ use std::process::Command;
 use std::{thread, time};
 
 use nitrokey::{
-    Authenticate, CommandError, Config, ConfigureOtp, Device, GenerateOtp, GetPasswordSafe,
-    OtpMode, OtpSlotData, Storage, VolumeMode,
+    Authenticate, CommandError, CommunicationError, Config, ConfigureOtp, Device, Error,
+    GenerateOtp, GetPasswordSafe, LibraryError, OtpMode, OtpSlotData, Storage, VolumeMode,
+    DEFAULT_ADMIN_PIN, DEFAULT_USER_PIN,
 };
 use nitrokey_test::test as test_device;
 
-use crate::util::{ADMIN_PASSWORD, USER_PASSWORD};
-
 static ADMIN_NEW_PASSWORD: &str = "1234567890";
 static UPDATE_PIN: &str = "12345678";
 static UPDATE_NEW_PIN: &str = "87654321";
@@ -31,31 +33,39 @@ fn count_nitrokey_block_devices() -> usize {
 
 #[test_device]
 fn connect_no_device() {
-    assert!(nitrokey::connect().is_err());
-    assert!(nitrokey::connect_model(nitrokey::Model::Pro).is_err());
-    assert!(nitrokey::connect_model(nitrokey::Model::Storage).is_err());
-    assert!(nitrokey::Pro::connect().is_err());
-    assert!(nitrokey::Storage::connect().is_err());
+    let mut manager = unwrap_ok!(nitrokey::take());
+
+    assert_cmu_err!(CommunicationError::NotConnected, manager.connect());
+    assert_cmu_err!(
+        CommunicationError::NotConnected,
+        manager.connect_model(nitrokey::Model::Pro)
+    );
+    assert_cmu_err!(
+        CommunicationError::NotConnected,
+        manager.connect_model(nitrokey::Model::Storage)
+    );
+    assert_cmu_err!(CommunicationError::NotConnected, manager.connect_pro());
+    assert_cmu_err!(CommunicationError::NotConnected, manager.connect_storage());
 }
 
 #[test_device]
 fn connect_pro(device: Pro) {
     assert_eq!(device.get_model(), nitrokey::Model::Pro);
-    drop(device);
 
-    assert!(nitrokey::connect().is_ok());
-    assert!(nitrokey::connect_model(nitrokey::Model::Pro).is_ok());
-    assert!(nitrokey::Pro::connect().is_ok());
+    let manager = device.into_manager();
+    assert_any_ok!(manager.connect());
+    assert_any_ok!(manager.connect_model(nitrokey::Model::Pro));
+    assert_any_ok!(manager.connect_pro());
 }
 
 #[test_device]
 fn connect_storage(device: Storage) {
     assert_eq!(device.get_model(), nitrokey::Model::Storage);
-    drop(device);
 
-    assert!(nitrokey::connect().is_ok());
-    assert!(nitrokey::connect_model(nitrokey::Model::Storage).is_ok());
-    assert!(nitrokey::Storage::connect().is_ok());
+    let manager = device.into_manager();
+    assert_any_ok!(manager.connect());
+    assert_any_ok!(manager.connect_model(nitrokey::Model::Storage));
+    assert_any_ok!(manager.connect_storage());
 }
 
 fn assert_empty_serial_number() {
@@ -75,36 +85,40 @@ fn disconnect(device: DeviceWrapper) {
 
 #[test_device]
 fn get_serial_number(device: DeviceWrapper) {
-    let result = device.get_serial_number();
-    assert!(result.is_ok());
-    let serial_number = result.unwrap();
+    let serial_number = unwrap_ok!(device.get_serial_number());
     assert!(serial_number.is_ascii());
     assert!(serial_number.chars().all(|c| c.is_ascii_hexdigit()));
 }
 #[test_device]
 fn get_firmware_version(device: Pro) {
-    assert_eq!(0, device.get_major_firmware_version());
-    let minor = device.get_minor_firmware_version();
-    assert!(minor > 0);
+    let version = unwrap_ok!(device.get_firmware_version());
+    assert_eq!(0, version.major);
+    assert!(version.minor > 0);
 }
 
-fn admin_retry<T: Authenticate + Device>(device: T, suffix: &str, count: u8) -> T {
-    let result = device.authenticate_admin(&(ADMIN_PASSWORD.to_owned() + suffix));
+fn admin_retry<'a, T>(device: T, suffix: &str, count: u8) -> T
+where
+    T: Authenticate<'a> + Device<'a> + 'a,
+{
+    let result = device.authenticate_admin(&(DEFAULT_ADMIN_PIN.to_owned() + suffix));
     let device = match result {
         Ok(admin) => admin.device(),
         Err((device, _)) => device,
     };
-    assert_eq!(count, device.get_admin_retry_count());
+    assert_ok!(count, device.get_admin_retry_count());
     return device;
 }
 
-fn user_retry<T: Authenticate + Device>(device: T, suffix: &str, count: u8) -> T {
-    let result = device.authenticate_user(&(USER_PASSWORD.to_owned() + suffix));
+fn user_retry<'a, T>(device: T, suffix: &str, count: u8) -> T
+where
+    T: Authenticate<'a> + Device<'a> + 'a,
+{
+    let result = device.authenticate_user(&(DEFAULT_USER_PIN.to_owned() + suffix));
     let device = match result {
         Ok(admin) => admin.device(),
         Err((device, _)) => device,
     };
-    assert_eq!(count, device.get_user_retry_count());
+    assert_ok!(count, device.get_user_retry_count());
     return device;
 }
 
@@ -123,326 +137,390 @@ fn get_retry_count(device: DeviceWrapper) {
 
 #[test_device]
 fn config(device: DeviceWrapper) {
-    let admin = device.authenticate_admin(ADMIN_PASSWORD).unwrap();
+    let mut admin = unwrap_ok!(device.authenticate_admin(DEFAULT_ADMIN_PIN));
+
     let config = Config::new(None, None, None, true);
-    assert_eq!(Ok(()), admin.write_config(config));
-    let get_config = admin.get_config().unwrap();
-    assert_eq!(config, get_config);
+    assert_ok!((), admin.write_config(config));
+    assert_ok!(config, admin.get_config());
 
     let config = Config::new(None, Some(9), None, true);
-    assert_eq!(Err(CommandError::InvalidSlot), admin.write_config(config));
+    assert_lib_err!(LibraryError::InvalidSlot, admin.write_config(config));
 
     let config = Config::new(Some(1), None, Some(0), false);
-    assert_eq!(Ok(()), admin.write_config(config));
-    let get_config = admin.get_config().unwrap();
-    assert_eq!(config, get_config);
+    assert_ok!((), admin.write_config(config));
+    assert_ok!(config, admin.get_config());
 
     let config = Config::new(None, None, None, false);
-    assert_eq!(Ok(()), admin.write_config(config));
-    let get_config = admin.get_config().unwrap();
-    assert_eq!(config, get_config);
+    assert_ok!((), admin.write_config(config));
+    assert_ok!(config, admin.get_config());
 }
 
 #[test_device]
 fn change_user_pin(device: DeviceWrapper) {
-    let device = device.authenticate_user(USER_PASSWORD).unwrap().device();
+    let device = device.authenticate_user(DEFAULT_USER_PIN).unwrap().device();
     let device = device.authenticate_user(USER_NEW_PASSWORD).unwrap_err().0;
 
-    assert!(device
-        .change_user_pin(USER_PASSWORD, USER_NEW_PASSWORD)
-        .is_ok());
+    let mut device = device;
+    assert_ok!(
+        (),
+        device.change_user_pin(DEFAULT_USER_PIN, USER_NEW_PASSWORD)
+    );
 
-    let device = device.authenticate_user(USER_PASSWORD).unwrap_err().0;
+    let device = device.authenticate_user(DEFAULT_USER_PIN).unwrap_err().0;
     let device = device
         .authenticate_user(USER_NEW_PASSWORD)
         .unwrap()
         .device();
 
-    let result = device.change_user_pin(USER_PASSWORD, USER_PASSWORD);
-    assert_eq!(Err(CommandError::WrongPassword), result);
+    let mut device = device;
+    let result = device.change_user_pin(DEFAULT_USER_PIN, DEFAULT_USER_PIN);
+    assert_cmd_err!(CommandError::WrongPassword, result);
 
-    assert!(device
-        .change_user_pin(USER_NEW_PASSWORD, USER_PASSWORD)
-        .is_ok());
+    assert_ok!(
+        (),
+        device.change_user_pin(USER_NEW_PASSWORD, DEFAULT_USER_PIN)
+    );
 
-    let device = device.authenticate_user(USER_PASSWORD).unwrap().device();
+    let device = device.authenticate_user(DEFAULT_USER_PIN).unwrap().device();
     assert!(device.authenticate_user(USER_NEW_PASSWORD).is_err());
 }
 
 #[test_device]
 fn change_admin_pin(device: DeviceWrapper) {
-    let device = device.authenticate_admin(ADMIN_PASSWORD).unwrap().device();
-    let device = device.authenticate_admin(ADMIN_NEW_PASSWORD).unwrap_err().0;
+    let device = device
+        .authenticate_admin(DEFAULT_ADMIN_PIN)
+        .unwrap()
+        .device();
+    let mut device = device.authenticate_admin(ADMIN_NEW_PASSWORD).unwrap_err().0;
 
-    assert!(device
-        .change_admin_pin(ADMIN_PASSWORD, ADMIN_NEW_PASSWORD)
-        .is_ok());
+    assert_ok!(
+        (),
+        device.change_admin_pin(DEFAULT_ADMIN_PIN, ADMIN_NEW_PASSWORD)
+    );
 
-    let device = device.authenticate_admin(ADMIN_PASSWORD).unwrap_err().0;
-    let device = device
+    let device = device.authenticate_admin(DEFAULT_ADMIN_PIN).unwrap_err().0;
+    let mut device = device
         .authenticate_admin(ADMIN_NEW_PASSWORD)
         .unwrap()
         .device();
 
-    assert_eq!(
-        Err(CommandError::WrongPassword),
-        device.change_admin_pin(ADMIN_PASSWORD, ADMIN_PASSWORD)
+    assert_cmd_err!(
+        CommandError::WrongPassword,
+        device.change_admin_pin(DEFAULT_ADMIN_PIN, DEFAULT_ADMIN_PIN)
     );
 
-    assert!(device
-        .change_admin_pin(ADMIN_NEW_PASSWORD, ADMIN_PASSWORD)
-        .is_ok());
+    assert_ok!(
+        (),
+        device.change_admin_pin(ADMIN_NEW_PASSWORD, DEFAULT_ADMIN_PIN)
+    );
 
-    let device = device.authenticate_admin(ADMIN_PASSWORD).unwrap().device();
+    let device = device
+        .authenticate_admin(DEFAULT_ADMIN_PIN)
+        .unwrap()
+        .device();
     device.authenticate_admin(ADMIN_NEW_PASSWORD).unwrap_err();
 }
 
-fn require_failed_user_login<D>(device: D, password: &str, error: CommandError) -> D
+fn require_failed_user_login<'a, D>(device: D, password: &str, error: CommandError) -> D
 where
-    D: Device + Authenticate,
-    nitrokey::User<D>: std::fmt::Debug,
+    D: Device<'a> + Authenticate<'a> + 'a,
+    nitrokey::User<'a, D>: std::fmt::Debug,
 {
     let result = device.authenticate_user(password);
     assert!(result.is_err());
     let err = result.unwrap_err();
-    assert_eq!(error, err.1);
+    match err.1 {
+        Error::CommandError(err) => assert_eq!(error, err),
+        _ => assert!(false),
+    };
     err.0
 }
 
 #[test_device]
 fn unlock_user_pin(device: DeviceWrapper) {
-    let device = device.authenticate_user(USER_PASSWORD).unwrap().device();
-    assert!(device
-        .unlock_user_pin(ADMIN_PASSWORD, USER_PASSWORD)
-        .is_ok());
-    assert_eq!(
-        Err(CommandError::WrongPassword),
-        device.unlock_user_pin(USER_PASSWORD, USER_PASSWORD)
+    let mut device = device.authenticate_user(DEFAULT_USER_PIN).unwrap().device();
+    assert_ok!(
+        (),
+        device.unlock_user_pin(DEFAULT_ADMIN_PIN, DEFAULT_USER_PIN)
+    );
+    assert_cmd_err!(
+        CommandError::WrongPassword,
+        device.unlock_user_pin(DEFAULT_USER_PIN, DEFAULT_USER_PIN)
     );
 
     // block user PIN
-    let wrong_password = USER_PASSWORD.to_owned() + "foo";
+    let wrong_password = DEFAULT_USER_PIN.to_owned() + "foo";
     let device = require_failed_user_login(device, &wrong_password, CommandError::WrongPassword);
     let device = require_failed_user_login(device, &wrong_password, CommandError::WrongPassword);
     let device = require_failed_user_login(device, &wrong_password, CommandError::WrongPassword);
-    let device = require_failed_user_login(device, USER_PASSWORD, CommandError::WrongPassword);
+    let mut device =
+        require_failed_user_login(device, DEFAULT_USER_PIN, CommandError::WrongPassword);
 
     // unblock with current PIN
-    assert_eq!(
-        Err(CommandError::WrongPassword),
-        device.unlock_user_pin(USER_PASSWORD, USER_PASSWORD)
+    assert_cmd_err!(
+        CommandError::WrongPassword,
+        device.unlock_user_pin(DEFAULT_USER_PIN, DEFAULT_USER_PIN)
     );
-    assert!(device
-        .unlock_user_pin(ADMIN_PASSWORD, USER_PASSWORD)
-        .is_ok());
-    let device = device.authenticate_user(USER_PASSWORD).unwrap().device();
+    assert_ok!(
+        (),
+        device.unlock_user_pin(DEFAULT_ADMIN_PIN, DEFAULT_USER_PIN)
+    );
+    let device = device.authenticate_user(DEFAULT_USER_PIN).unwrap().device();
 
     // block user PIN
     let device = require_failed_user_login(device, &wrong_password, CommandError::WrongPassword);
     let device = require_failed_user_login(device, &wrong_password, CommandError::WrongPassword);
     let device = require_failed_user_login(device, &wrong_password, CommandError::WrongPassword);
-    let device = require_failed_user_login(device, USER_PASSWORD, CommandError::WrongPassword);
+    let mut device =
+        require_failed_user_login(device, DEFAULT_USER_PIN, CommandError::WrongPassword);
 
     // unblock with new PIN
-    assert_eq!(
-        Err(CommandError::WrongPassword),
-        device.unlock_user_pin(USER_PASSWORD, USER_PASSWORD)
+    assert_cmd_err!(
+        CommandError::WrongPassword,
+        device.unlock_user_pin(DEFAULT_USER_PIN, DEFAULT_USER_PIN)
+    );
+    assert_ok!(
+        (),
+        device.unlock_user_pin(DEFAULT_ADMIN_PIN, USER_NEW_PASSWORD)
     );
-    assert!(device
-        .unlock_user_pin(ADMIN_PASSWORD, USER_NEW_PASSWORD)
-        .is_ok());
 
     // reset user PIN
-    assert!(device
-        .change_user_pin(USER_NEW_PASSWORD, USER_PASSWORD)
-        .is_ok());
+    assert_ok!(
+        (),
+        device.change_user_pin(USER_NEW_PASSWORD, DEFAULT_USER_PIN)
+    );
+}
+
+fn assert_utf8_err_or_ne(left: &str, right: Result<String, Error>) {
+    match right {
+        Ok(s) => assert_ne!(left.to_string(), s),
+        Err(Error::Utf8Error(_)) => {}
+        Err(err) => panic!("Expected Utf8Error, got {}!", err),
+    }
 }
 
 #[test_device]
 fn factory_reset(device: DeviceWrapper) {
-    let admin = device.authenticate_admin(ADMIN_PASSWORD).unwrap();
+    let mut admin = unwrap_ok!(device.authenticate_admin(DEFAULT_ADMIN_PIN));
     let otp_data = OtpSlotData::new(1, "test", "0123468790", OtpMode::SixDigits);
-    assert_eq!(Ok(()), admin.write_totp_slot(otp_data, 30));
+    assert_ok!((), admin.write_totp_slot(otp_data, 30));
 
-    let device = admin.device();
-    let pws = device.get_password_safe(USER_PASSWORD).unwrap();
-    assert_eq!(Ok(()), pws.write_slot(0, "test", "testlogin", "testpw"));
+    let mut device = admin.device();
+    let mut pws = unwrap_ok!(device.get_password_safe(DEFAULT_USER_PIN));
+    assert_ok!((), pws.write_slot(0, "test", "testlogin", "testpw"));
     drop(pws);
 
-    assert_eq!(
-        Ok(()),
-        device.change_user_pin(USER_PASSWORD, USER_NEW_PASSWORD)
+    assert_ok!(
+        (),
+        device.change_user_pin(DEFAULT_USER_PIN, USER_NEW_PASSWORD)
     );
-    assert_eq!(
-        Ok(()),
-        device.change_admin_pin(ADMIN_PASSWORD, ADMIN_NEW_PASSWORD)
+    assert_ok!(
+        (),
+        device.change_admin_pin(DEFAULT_ADMIN_PIN, ADMIN_NEW_PASSWORD)
     );
 
-    assert_eq!(
-        Err(CommandError::WrongPassword),
+    assert_cmd_err!(
+        CommandError::WrongPassword,
         device.factory_reset(USER_NEW_PASSWORD)
     );
-    assert_eq!(
-        Err(CommandError::WrongPassword),
-        device.factory_reset(ADMIN_PASSWORD)
+    assert_cmd_err!(
+        CommandError::WrongPassword,
+        device.factory_reset(DEFAULT_ADMIN_PIN)
     );
-    assert_eq!(Ok(()), device.factory_reset(ADMIN_NEW_PASSWORD));
+    assert_ok!((), device.factory_reset(ADMIN_NEW_PASSWORD));
 
-    let device = device.authenticate_admin(ADMIN_PASSWORD).unwrap().device();
+    let device = device
+        .authenticate_admin(DEFAULT_ADMIN_PIN)
+        .unwrap()
+        .device();
 
-    let user = device.authenticate_user(USER_PASSWORD).unwrap();
-    assert_eq!(
-        Err(CommandError::SlotNotProgrammed),
-        user.get_totp_slot_name(1)
-    );
+    let user = unwrap_ok!(device.authenticate_user(DEFAULT_USER_PIN));
+    assert_cmd_err!(CommandError::SlotNotProgrammed, user.get_totp_slot_name(1));
 
-    let device = user.device();
-    let pws = device.get_password_safe(USER_PASSWORD).unwrap();
-    assert_ne!("test".to_string(), pws.get_slot_name(0).unwrap());
-    assert_ne!("testlogin".to_string(), pws.get_slot_login(0).unwrap());
-    assert_ne!("testpw".to_string(), pws.get_slot_password(0).unwrap());
+    let mut device = user.device();
+    let pws = unwrap_ok!(device.get_password_safe(DEFAULT_USER_PIN));
+    assert_utf8_err_or_ne("test", pws.get_slot_name(0));
+    assert_utf8_err_or_ne("testlogin", pws.get_slot_login(0));
+    assert_utf8_err_or_ne("testpw", pws.get_slot_password(0));
+    drop(pws);
 
-    assert_eq!(Ok(()), device.build_aes_key(ADMIN_PASSWORD));
+    assert_ok!(3, device.get_user_retry_count());
+    assert_ok!((), device.build_aes_key(DEFAULT_ADMIN_PIN));
 }
 
 #[test_device]
 fn build_aes_key(device: DeviceWrapper) {
-    let pws = device.get_password_safe(USER_PASSWORD).unwrap();
-    assert_eq!(Ok(()), pws.write_slot(0, "test", "testlogin", "testpw"));
+    let mut device = device;
+    let mut pws = unwrap_ok!(device.get_password_safe(DEFAULT_USER_PIN));
+    assert_ok!((), pws.write_slot(0, "test", "testlogin", "testpw"));
     drop(pws);
 
-    assert_eq!(
-        Err(CommandError::WrongPassword),
-        device.build_aes_key(USER_PASSWORD)
+    assert_cmd_err!(
+        CommandError::WrongPassword,
+        device.build_aes_key(DEFAULT_USER_PIN)
     );
-    assert_eq!(Ok(()), device.build_aes_key(ADMIN_PASSWORD));
+    assert_ok!((), device.build_aes_key(DEFAULT_ADMIN_PIN));
 
-    let device = device.authenticate_admin(ADMIN_PASSWORD).unwrap().device();
+    let mut device = device
+        .authenticate_admin(DEFAULT_ADMIN_PIN)
+        .unwrap()
+        .device();
 
-    let pws = device.get_password_safe(USER_PASSWORD).unwrap();
-    assert_ne!("test".to_string(), pws.get_slot_name(0).unwrap());
-    assert_ne!("testlogin".to_string(), pws.get_slot_login(0).unwrap());
-    assert_ne!("testpw".to_string(), pws.get_slot_password(0).unwrap());
+    let pws = unwrap_ok!(device.get_password_safe(DEFAULT_USER_PIN));
+    assert_utf8_err_or_ne("test", pws.get_slot_name(0));
+    assert_utf8_err_or_ne("testlogin", pws.get_slot_login(0));
+    assert_utf8_err_or_ne("testpw", pws.get_slot_password(0));
 }
 
 #[test_device]
 fn change_update_pin(device: Storage) {
-    assert_eq!(
-        Err(CommandError::WrongPassword),
+    let mut device = device;
+    assert_cmd_err!(
+        CommandError::WrongPassword,
         device.change_update_pin(UPDATE_NEW_PIN, UPDATE_PIN)
     );
-    assert_eq!(Ok(()), device.change_update_pin(UPDATE_PIN, UPDATE_NEW_PIN));
-    assert_eq!(Ok(()), device.change_update_pin(UPDATE_NEW_PIN, UPDATE_PIN));
+    assert_ok!((), device.change_update_pin(UPDATE_PIN, UPDATE_NEW_PIN));
+    assert_ok!((), device.change_update_pin(UPDATE_NEW_PIN, UPDATE_PIN));
 }
 
 #[test_device]
 fn encrypted_volume(device: Storage) {
-    assert_eq!(Ok(()), device.lock());
+    let mut device = device;
+    assert_ok!((), device.lock());
 
     assert_eq!(1, count_nitrokey_block_devices());
-    assert_eq!(Ok(()), device.disable_encrypted_volume());
+    assert_ok!((), device.disable_encrypted_volume());
     assert_eq!(1, count_nitrokey_block_devices());
-    assert_eq!(
-        Err(CommandError::WrongPassword),
+    assert_cmd_err!(
+        CommandError::WrongPassword,
         device.enable_encrypted_volume("123")
     );
     assert_eq!(1, count_nitrokey_block_devices());
-    assert_eq!(Ok(()), device.enable_encrypted_volume(USER_PASSWORD));
+    assert_ok!((), device.enable_encrypted_volume(DEFAULT_USER_PIN));
     assert_eq!(2, count_nitrokey_block_devices());
-    assert_eq!(Ok(()), device.disable_encrypted_volume());
+    assert_ok!((), device.disable_encrypted_volume());
     assert_eq!(1, count_nitrokey_block_devices());
 }
 
 #[test_device]
 fn hidden_volume(device: Storage) {
-    assert_eq!(Ok(()), device.lock());
+    let mut device = device;
+    assert_ok!((), device.lock());
 
     assert_eq!(1, count_nitrokey_block_devices());
-    assert_eq!(Ok(()), device.disable_hidden_volume());
+    assert_ok!((), device.disable_hidden_volume());
     assert_eq!(1, count_nitrokey_block_devices());
 
-    assert_eq!(Ok(()), device.enable_encrypted_volume(USER_PASSWORD));
+    assert_ok!((), device.enable_encrypted_volume(DEFAULT_USER_PIN));
     assert_eq!(2, count_nitrokey_block_devices());
 
     // TODO: why this error code?
-    assert_eq!(
-        Err(CommandError::WrongPassword),
+    assert_cmd_err!(
+        CommandError::WrongPassword,
         device.create_hidden_volume(5, 0, 100, "hiddenpw")
     );
-    assert_eq!(Ok(()), device.create_hidden_volume(0, 20, 21, "hidden-pw"));
-    assert_eq!(
-        Ok(()),
-        device.create_hidden_volume(0, 20, 21, "hiddenpassword")
-    );
-    assert_eq!(Ok(()), device.create_hidden_volume(1, 0, 1, "otherpw"));
+    assert_ok!((), device.create_hidden_volume(0, 20, 21, "hidden-pw"));
+    assert_ok!((), device.create_hidden_volume(0, 20, 21, "hiddenpassword"));
+    assert_ok!((), device.create_hidden_volume(1, 0, 1, "otherpw"));
     // TODO: test invalid range (not handled by libnitrokey)
     assert_eq!(2, count_nitrokey_block_devices());
 
-    assert_eq!(
-        Err(CommandError::WrongPassword),
+    assert_cmd_err!(
+        CommandError::WrongPassword,
         device.enable_hidden_volume("blubb")
     );
-    assert_eq!(Ok(()), device.enable_hidden_volume("hiddenpassword"));
+    assert_ok!((), device.enable_hidden_volume("hiddenpassword"));
     assert_eq!(2, count_nitrokey_block_devices());
-    assert_eq!(Ok(()), device.enable_hidden_volume("otherpw"));
+    assert_ok!((), device.enable_hidden_volume("otherpw"));
     assert_eq!(2, count_nitrokey_block_devices());
 
-    assert_eq!(Ok(()), device.disable_hidden_volume());
+    assert_ok!((), device.disable_hidden_volume());
     assert_eq!(1, count_nitrokey_block_devices());
 }
 
 #[test_device]
 fn lock(device: Storage) {
-    assert_eq!(Ok(()), device.enable_encrypted_volume(USER_PASSWORD));
-    assert_eq!(Ok(()), device.lock());
+    let mut device = device;
+    assert_ok!((), device.enable_encrypted_volume(DEFAULT_USER_PIN));
+    assert_ok!((), device.lock());
     assert_eq!(1, count_nitrokey_block_devices());
 }
 
 #[test_device]
+fn set_encrypted_volume_mode(device: Storage) {
+    // This test case does not check the device status as the command only works with firmware
+    // version 0.49.  For later versions, it does not do anything and always returns Ok(()).
+    let mut device = device;
+
+    assert_ok!(
+        (),
+        device.set_encrypted_volume_mode(DEFAULT_ADMIN_PIN, VolumeMode::ReadOnly)
+    );
+
+    // TODO: re-enable once the password is checked in the firmware
+    // assert_cmd_err!(
+    //     CommandError::WrongPassword,
+    //     device.set_encrypted_volume_mode(DEFAULT_USER_PIN, VolumeMode::ReadOnly)
+    // );
+
+    assert_ok!(
+        (),
+        device.set_encrypted_volume_mode(DEFAULT_ADMIN_PIN, VolumeMode::ReadOnly)
+    );
+    assert_ok!(
+        (),
+        device.set_encrypted_volume_mode(DEFAULT_ADMIN_PIN, VolumeMode::ReadWrite)
+    );
+    assert_ok!(
+        (),
+        device.set_encrypted_volume_mode(DEFAULT_ADMIN_PIN, VolumeMode::ReadOnly)
+    );
+}
+
+#[test_device]
 fn set_unencrypted_volume_mode(device: Storage) {
     fn assert_mode(device: &Storage, mode: VolumeMode) {
-        let status = device.get_status();
-        assert!(status.is_ok());
+        let status = unwrap_ok!(device.get_status());
         assert_eq!(
-            status.unwrap().unencrypted_volume.read_only,
+            status.unencrypted_volume.read_only,
             mode == VolumeMode::ReadOnly
         );
     }
 
-    fn assert_success(device: &Storage, mode: VolumeMode) {
-        assert_eq!(
-            Ok(()),
-            device.set_unencrypted_volume_mode(ADMIN_PASSWORD, mode)
+    fn assert_success(device: &mut Storage, mode: VolumeMode) {
+        assert_ok!(
+            (),
+            device.set_unencrypted_volume_mode(DEFAULT_ADMIN_PIN, mode)
         );
         assert_mode(&device, mode);
     }
 
-    assert_success(&device, VolumeMode::ReadOnly);
+    let mut device = device;
+    assert_success(&mut device, VolumeMode::ReadOnly);
 
-    assert_eq!(
-        Err(CommandError::WrongPassword),
-        device.set_unencrypted_volume_mode(USER_PASSWORD, VolumeMode::ReadOnly)
+    assert_cmd_err!(
+        CommandError::WrongPassword,
+        device.set_unencrypted_volume_mode(DEFAULT_USER_PIN, VolumeMode::ReadOnly)
     );
     assert_mode(&device, VolumeMode::ReadOnly);
 
-    assert_success(&device, VolumeMode::ReadWrite);
-    assert_success(&device, VolumeMode::ReadWrite);
-    assert_success(&device, VolumeMode::ReadOnly);
+    assert_success(&mut device, VolumeMode::ReadWrite);
+    assert_success(&mut device, VolumeMode::ReadWrite);
+    assert_success(&mut device, VolumeMode::ReadOnly);
 }
 
 #[test_device]
 fn get_storage_status(device: Storage) {
-    let status = device.get_status().unwrap();
-
+    let status = unwrap_ok!(device.get_status());
     assert!(status.serial_number_sd_card > 0);
     assert!(status.serial_number_smart_card > 0);
 }
 
 #[test_device]
 fn get_production_info(device: Storage) {
-    let info = device.get_production_info().unwrap();
-    assert_eq!(0, info.firmware_version_major);
-    assert!(info.firmware_version_minor != 0);
+    let info = unwrap_ok!(device.get_production_info());
+    assert_eq!(0, info.firmware_version.major);
+    assert!(info.firmware_version.minor != 0);
     assert!(info.serial_number_cpu != 0);
     assert!(info.sd_card.serial_number != 0);
     assert!(info.sd_card.size > 0);
@@ -453,44 +531,45 @@ fn get_production_info(device: Storage) {
     assert!(info.sd_card.oem != 0);
     assert!(info.sd_card.manufacturer != 0);
 
-    let status = device.get_status().unwrap();
-    assert_eq!(status.firmware_version_major, info.firmware_version_major);
-    assert_eq!(status.firmware_version_minor, info.firmware_version_minor);
+    let status = unwrap_ok!(device.get_status());
+    assert_eq!(status.firmware_version, info.firmware_version);
     assert_eq!(status.serial_number_sd_card, info.sd_card.serial_number);
 }
 
 #[test_device]
 fn clear_new_sd_card_warning(device: Storage) {
-    assert_eq!(Ok(()), device.factory_reset(ADMIN_PASSWORD));
+    let mut device = device;
+    assert_ok!((), device.factory_reset(DEFAULT_ADMIN_PIN));
     thread::sleep(time::Duration::from_secs(3));
-    assert_eq!(Ok(()), device.build_aes_key(ADMIN_PASSWORD));
+    assert_ok!((), device.build_aes_key(DEFAULT_ADMIN_PIN));
 
     // We have to perform an SD card operation to reset the new_sd_card_found field
-    assert_eq!(Ok(()), device.lock());
+    assert_ok!((), device.lock());
 
-    let status = device.get_status().unwrap();
+    let status = unwrap_ok!(device.get_status());
     assert!(status.new_sd_card_found);
 
-    assert_eq!(Ok(()), device.clear_new_sd_card_warning(ADMIN_PASSWORD));
+    assert_ok!((), device.clear_new_sd_card_warning(DEFAULT_ADMIN_PIN));
 
-    let status = device.get_status().unwrap();
+    let status = unwrap_ok!(device.get_status());
     assert!(!status.new_sd_card_found);
 }
 
 #[test_device]
 fn export_firmware(device: Storage) {
-    assert_eq!(
-        Err(CommandError::WrongPassword),
+    let mut device = device;
+    assert_cmd_err!(
+        CommandError::WrongPassword,
         device.export_firmware("someadminpn")
     );
-    assert_eq!(Ok(()), device.export_firmware(ADMIN_PASSWORD));
-    assert_eq!(
-        Ok(()),
-        device.set_unencrypted_volume_mode(ADMIN_PASSWORD, VolumeMode::ReadWrite)
+    assert_ok!((), device.export_firmware(DEFAULT_ADMIN_PIN));
+    assert_ok!(
+        (),
+        device.set_unencrypted_volume_mode(DEFAULT_ADMIN_PIN, VolumeMode::ReadWrite)
     );
-    assert_eq!(Ok(()), device.export_firmware(ADMIN_PASSWORD));
-    assert_eq!(
-        Ok(()),
-        device.set_unencrypted_volume_mode(ADMIN_PASSWORD, VolumeMode::ReadOnly)
+    assert_ok!((), device.export_firmware(DEFAULT_ADMIN_PIN));
+    assert_ok!(
+        (),
+        device.set_unencrypted_volume_mode(DEFAULT_ADMIN_PIN, VolumeMode::ReadOnly)
     );
 }
diff --git a/tests/lib.rs b/tests/lib.rs
index c92e224..25aae0f 100644
--- a/tests/lib.rs
+++ b/tests/lib.rs
@@ -1,7 +1,28 @@
+// Copyright (C) 2019 Robin Krahl <robin.krahl@ireas.org>
+// SPDX-License-Identifier: MIT
+
+mod util;
+
 #[test]
 fn get_library_version() {
-    let version = nitrokey::get_library_version();
+    let version = unwrap_ok!(nitrokey::get_library_version());
 
     assert!(version.git.is_empty() || version.git.starts_with("v"));
     assert!(version.major > 0);
 }
+
+#[test]
+fn take_manager() {
+    assert!(nitrokey::take().is_ok());
+
+    let result = nitrokey::take();
+    assert!(result.is_ok());
+    let result2 = nitrokey::take();
+    match result2 {
+        Ok(_) => panic!("Expected error, got Ok(_)!"),
+        Err(nitrokey::Error::ConcurrentAccessError) => {}
+        Err(err) => panic!("Expected ConcurrentAccessError, got {}", err),
+    }
+    drop(result);
+    assert!(nitrokey::take().is_ok());
+}
diff --git a/tests/otp.rs b/tests/otp.rs
index 712f7a2..38cd8a9 100644
--- a/tests/otp.rs
+++ b/tests/otp.rs
@@ -1,16 +1,17 @@
+// Copyright (C) 2018-2019 Robin Krahl <robin.krahl@ireas.org>
+// SPDX-License-Identifier: MIT
+
 mod util;
 
 use std::fmt::Debug;
-use std::ops::Deref;
+use std::ops::DerefMut;
 
 use nitrokey::{
-    Admin, Authenticate, CommandError, Config, ConfigureOtp, Device, GenerateOtp, OtpMode,
-    OtpSlotData,
+    Admin, Authenticate, CommandError, Config, ConfigureOtp, Device, GenerateOtp, LibraryError,
+    OtpMode, OtpSlotData, DEFAULT_ADMIN_PIN, DEFAULT_USER_PIN,
 };
 use nitrokey_test::test as test_device;
 
-use crate::util::{ADMIN_PASSWORD, USER_PASSWORD};
-
 // test suite according to RFC 4226, Appendix D
 static HOTP_SECRET: &str = "3132333435363738393031323334353637383930";
 static HOTP_CODES: &[&str] = &[
@@ -20,13 +21,13 @@ static HOTP_CODES: &[&str] = &[
 
 // test suite according to RFC 6238, Appendix B
 static TOTP_SECRET: &str = "3132333435363738393031323334353637383930";
-static TOTP_CODES: &[(u64, &str)] = &[
-    (59, "94287082"),
-    (1111111109, "07081804"),
-    (1111111111, "14050471"),
-    (1234567890, "89005924"),
-    (2000000000, "69279037"),
-    (20000000000, "65353130"),
+static TOTP_CODES: &[(u64, &[&str])] = &[
+    (59, &["94287082", "37359152"]),
+    (1111111109, &["07081804"]),
+    (1111111111, &["14050471"]),
+    (1234567890, &["89005924"]),
+    (2000000000, &["69279037"]),
+    (20000000000, &["65353130"]),
 ];
 
 #[derive(PartialEq)]
@@ -35,268 +36,252 @@ enum TotpTimestampSize {
     U64,
 }
 
-fn make_admin_test_device<T>(device: T) -> Admin<T>
+fn make_admin_test_device<'a, T>(device: T) -> Admin<'a, T>
 where
-    T: Device,
-    (T, nitrokey::CommandError): Debug,
+    T: Device<'a>,
+    (T, nitrokey::Error): Debug,
 {
-    device
-        .authenticate_admin(ADMIN_PASSWORD)
-        .expect("Could not login as admin.")
+    unwrap_ok!(device.authenticate_admin(DEFAULT_ADMIN_PIN))
 }
 
-fn configure_hotp(admin: &ConfigureOtp, counter: u8) {
+fn configure_hotp(admin: &mut dyn ConfigureOtp, counter: u8) {
     let slot_data = OtpSlotData::new(1, "test-hotp", HOTP_SECRET, OtpMode::SixDigits);
-    assert_eq!(Ok(()), admin.write_hotp_slot(slot_data, counter.into()));
+    assert_ok!((), admin.write_hotp_slot(slot_data, counter.into()));
 }
 
-fn check_hotp_codes(device: &GenerateOtp, offset: u8) {
+fn check_hotp_codes(device: &mut dyn GenerateOtp, offset: u8) {
     HOTP_CODES.iter().enumerate().for_each(|(i, code)| {
         if i >= offset as usize {
-            let result = device.get_hotp_code(1);
-            assert_eq!(code, &result.unwrap());
+            assert_ok!(code.to_string(), device.get_hotp_code(1));
         }
     });
 }
 
 #[test_device]
 fn set_time(device: DeviceWrapper) {
-    assert_eq!(Ok(()), device.set_time(1546385382, true));
-    assert_eq!(Ok(()), device.set_time(1546385392, false));
-    assert_eq!(
-        Err(CommandError::Timestamp),
-        device.set_time(1546385292, false)
-    );
-    assert_eq!(Ok(()), device.set_time(1546385382, true));
+    let mut device = device;
+    assert_ok!((), device.set_time(1546385382, true));
+    assert_ok!((), device.set_time(1546385392, false));
+    assert_cmd_err!(CommandError::Timestamp, device.set_time(1546385292, false));
+    assert_ok!((), device.set_time(1546385382, true));
 }
 
 #[test_device]
 fn hotp_no_pin(device: DeviceWrapper) {
-    let admin = make_admin_test_device(device);
+    let mut admin = make_admin_test_device(device);
     let config = Config::new(None, None, None, false);
-    assert_eq!(Ok(()), admin.write_config(config));
+    assert_ok!((), admin.write_config(config));
 
-    configure_hotp(&admin, 0);
-    check_hotp_codes(admin.deref(), 0);
+    configure_hotp(&mut admin, 0);
+    check_hotp_codes(admin.deref_mut(), 0);
 
-    configure_hotp(&admin, 5);
-    check_hotp_codes(admin.deref(), 5);
+    configure_hotp(&mut admin, 5);
+    check_hotp_codes(admin.deref_mut(), 5);
 
-    configure_hotp(&admin, 0);
-    check_hotp_codes(&admin.device(), 0);
+    configure_hotp(&mut admin, 0);
+    check_hotp_codes(&mut admin.device(), 0);
 }
 
 #[test_device]
 fn hotp_pin(device: DeviceWrapper) {
-    let admin = make_admin_test_device(device);
+    let mut admin = make_admin_test_device(device);
     let config = Config::new(None, None, None, true);
-    assert_eq!(Ok(()), admin.write_config(config));
+    assert_ok!((), admin.write_config(config));
 
-    configure_hotp(&admin, 0);
-    let user = admin.device().authenticate_user(USER_PASSWORD).unwrap();
-    check_hotp_codes(&user, 0);
+    configure_hotp(&mut admin, 0);
+    let mut user = unwrap_ok!(admin.device().authenticate_user(DEFAULT_USER_PIN));
+    check_hotp_codes(&mut user, 0);
 
-    assert!(user.device().get_hotp_code(1).is_err());
+    assert_cmd_err!(CommandError::NotAuthorized, user.device().get_hotp_code(1));
 }
 
 #[test_device]
 fn hotp_slot_name(device: DeviceWrapper) {
-    let admin = make_admin_test_device(device);
+    let mut admin = make_admin_test_device(device);
     let slot_data = OtpSlotData::new(1, "test-hotp", HOTP_SECRET, OtpMode::SixDigits);
-    assert_eq!(Ok(()), admin.write_hotp_slot(slot_data, 0));
+    assert_ok!((), admin.write_hotp_slot(slot_data, 0));
 
     let device = admin.device();
-    let result = device.get_hotp_slot_name(1);
-    assert_eq!("test-hotp", result.unwrap());
-    let result = device.get_hotp_slot_name(4);
-    assert_eq!(CommandError::InvalidSlot, result.unwrap_err());
+    assert_ok!("test-hotp".to_string(), device.get_hotp_slot_name(1));
+    assert_lib_err!(LibraryError::InvalidSlot, device.get_hotp_slot_name(4));
 }
 
 #[test_device]
 fn hotp_error(device: DeviceWrapper) {
-    let admin = make_admin_test_device(device);
+    let mut admin = make_admin_test_device(device);
     let slot_data = OtpSlotData::new(1, "", HOTP_SECRET, OtpMode::SixDigits);
-    assert_eq!(
-        Err(CommandError::NoName),
-        admin.write_hotp_slot(slot_data, 0)
-    );
+    assert_cmd_err!(CommandError::NoName, admin.write_hotp_slot(slot_data, 0));
     let slot_data = OtpSlotData::new(4, "test", HOTP_SECRET, OtpMode::SixDigits);
-    assert_eq!(
-        Err(CommandError::InvalidSlot),
+    assert_lib_err!(
+        LibraryError::InvalidSlot,
         admin.write_hotp_slot(slot_data, 0)
     );
     let slot_data = OtpSlotData::new(1, "test", "foobar", OtpMode::SixDigits);
-    assert_eq!(
-        Err(CommandError::InvalidHexString),
+    assert_lib_err!(
+        LibraryError::InvalidHexString,
         admin.write_hotp_slot(slot_data, 0)
     );
     let code = admin.get_hotp_code(4);
-    assert_eq!(CommandError::InvalidSlot, code.unwrap_err());
+    assert_lib_err!(LibraryError::InvalidSlot, code);
 }
 
 #[test_device]
 fn hotp_erase(device: DeviceWrapper) {
-    let admin = make_admin_test_device(device);
+    let mut admin = make_admin_test_device(device);
     let config = Config::new(None, None, None, false);
-    assert_eq!(Ok(()), admin.write_config(config));
+    assert_ok!((), admin.write_config(config));
     let slot_data = OtpSlotData::new(1, "test1", HOTP_SECRET, OtpMode::SixDigits);
-    assert_eq!(Ok(()), admin.write_hotp_slot(slot_data, 0));
+    assert_ok!((), admin.write_hotp_slot(slot_data, 0));
     let slot_data = OtpSlotData::new(2, "test2", HOTP_SECRET, OtpMode::SixDigits);
-    assert_eq!(Ok(()), admin.write_hotp_slot(slot_data, 0));
+    assert_ok!((), admin.write_hotp_slot(slot_data, 0));
 
-    assert_eq!(Ok(()), admin.erase_hotp_slot(1));
+    assert_ok!((), admin.erase_hotp_slot(1));
 
-    let device = admin.device();
+    let mut device = admin.device();
     let result = device.get_hotp_slot_name(1);
-    assert_eq!(CommandError::SlotNotProgrammed, result.unwrap_err());
+    assert_cmd_err!(CommandError::SlotNotProgrammed, result);
     let result = device.get_hotp_code(1);
-    assert_eq!(CommandError::SlotNotProgrammed, result.unwrap_err());
+    assert_cmd_err!(CommandError::SlotNotProgrammed, result);
 
-    assert_eq!("test2", device.get_hotp_slot_name(2).unwrap());
+    assert_ok!("test2".to_string(), device.get_hotp_slot_name(2));
 }
 
-fn configure_totp(admin: &ConfigureOtp, factor: u64) {
+fn configure_totp(admin: &mut dyn ConfigureOtp, factor: u64) {
     let slot_data = OtpSlotData::new(1, "test-totp", TOTP_SECRET, OtpMode::EightDigits);
     let time_window = 30u64.checked_mul(factor).unwrap();
-    assert_eq!(Ok(()), admin.write_totp_slot(slot_data, time_window as u16));
+    assert_ok!((), admin.write_totp_slot(slot_data, time_window as u16));
 }
 
-fn check_totp_codes(device: &GenerateOtp, factor: u64, timestamp_size: TotpTimestampSize) {
-    for (i, &(base_time, code)) in TOTP_CODES.iter().enumerate() {
+fn check_totp_codes(device: &mut dyn GenerateOtp, factor: u64, timestamp_size: TotpTimestampSize) {
+    for (base_time, codes) in TOTP_CODES {
         let time = base_time.checked_mul(factor).unwrap();
         let is_u64 = time > u32::max_value() as u64;
         if is_u64 != (timestamp_size == TotpTimestampSize::U64) {
             continue;
         }
 
-        assert_eq!(Ok(()), device.set_time(time, true));
-        let result = device.get_totp_code(1);
-        assert!(result.is_ok());
-        let result_code = result.unwrap();
-        assert_eq!(
-            code, result_code,
-            "TOTP code {} should be {} but is {}",
-            i, code, result_code
+        assert_ok!((), device.set_time(time, true));
+        let code = unwrap_ok!(device.get_totp_code(1));
+        assert!(
+            code.contains(&code),
+            "Generated TOTP code {} for {}, but expected one of {}",
+            code,
+            base_time,
+            codes.join(", ")
         );
     }
 }
 
 #[test_device]
 fn totp_no_pin(device: DeviceWrapper) {
-    // TODO: this test may fail due to bad timing --> find solution
-    let admin = make_admin_test_device(device);
+    let mut admin = make_admin_test_device(device);
     let config = Config::new(None, None, None, false);
-    assert_eq!(Ok(()), admin.write_config(config));
+    assert_ok!((), admin.write_config(config));
 
-    configure_totp(&admin, 1);
-    check_totp_codes(admin.deref(), 1, TotpTimestampSize::U32);
+    configure_totp(&mut admin, 1);
+    check_totp_codes(admin.deref_mut(), 1, TotpTimestampSize::U32);
 
-    configure_totp(&admin, 2);
-    check_totp_codes(admin.deref(), 2, TotpTimestampSize::U32);
+    configure_totp(&mut admin, 2);
+    check_totp_codes(admin.deref_mut(), 2, TotpTimestampSize::U32);
 
-    configure_totp(&admin, 1);
-    check_totp_codes(&admin.device(), 1, TotpTimestampSize::U32);
+    configure_totp(&mut admin, 1);
+    check_totp_codes(&mut admin.device(), 1, TotpTimestampSize::U32);
 }
 
 #[test_device]
 // Nitrokey Storage does only support timestamps that fit in a 32-bit
 // unsigned integer, so don't test with it.
 fn totp_no_pin_64(device: Pro) {
-    let admin = make_admin_test_device(device);
+    let mut admin = make_admin_test_device(device);
     let config = Config::new(None, None, None, false);
-    assert_eq!(Ok(()), admin.write_config(config));
+    assert_ok!((), admin.write_config(config));
 
-    configure_totp(&admin, 1);
-    check_totp_codes(admin.deref(), 1, TotpTimestampSize::U64);
+    configure_totp(&mut admin, 1);
+    check_totp_codes(admin.deref_mut(), 1, TotpTimestampSize::U64);
 
-    configure_totp(&admin, 2);
-    check_totp_codes(admin.deref(), 2, TotpTimestampSize::U64);
+    configure_totp(&mut admin, 2);
+    check_totp_codes(admin.deref_mut(), 2, TotpTimestampSize::U64);
 
-    configure_totp(&admin, 1);
-    check_totp_codes(&admin.device(), 1, TotpTimestampSize::U64);
+    configure_totp(&mut admin, 1);
+    check_totp_codes(&mut admin.device(), 1, TotpTimestampSize::U64);
 }
 
 #[test_device]
 fn totp_pin(device: DeviceWrapper) {
-    // TODO: this test may fail due to bad timing --> find solution
-    let admin = make_admin_test_device(device);
+    let mut admin = make_admin_test_device(device);
     let config = Config::new(None, None, None, true);
-    assert_eq!(Ok(()), admin.write_config(config));
+    assert_ok!((), admin.write_config(config));
 
-    configure_totp(&admin, 1);
-    let user = admin.device().authenticate_user(USER_PASSWORD).unwrap();
-    check_totp_codes(&user, 1, TotpTimestampSize::U32);
+    configure_totp(&mut admin, 1);
+    let mut user = unwrap_ok!(admin.device().authenticate_user(DEFAULT_USER_PIN));
+    check_totp_codes(&mut user, 1, TotpTimestampSize::U32);
 
-    assert!(user.device().get_totp_code(1).is_err());
+    assert_cmd_err!(CommandError::NotAuthorized, user.device().get_totp_code(1));
 }
 
 #[test_device]
 // See comment for totp_no_pin_64.
 fn totp_pin_64(device: Pro) {
-    let admin = make_admin_test_device(device);
+    let mut admin = make_admin_test_device(device);
     let config = Config::new(None, None, None, true);
-    assert_eq!(Ok(()), admin.write_config(config));
+    assert_ok!((), admin.write_config(config));
 
-    configure_totp(&admin, 1);
-    let user = admin.device().authenticate_user(USER_PASSWORD).unwrap();
-    check_totp_codes(&user, 1, TotpTimestampSize::U64);
+    configure_totp(&mut admin, 1);
+    let mut user = unwrap_ok!(admin.device().authenticate_user(DEFAULT_USER_PIN));
+    check_totp_codes(&mut user, 1, TotpTimestampSize::U64);
 
-    assert!(user.device().get_totp_code(1).is_err());
+    assert_cmd_err!(CommandError::NotAuthorized, user.device().get_totp_code(1));
 }
 
 #[test_device]
 fn totp_slot_name(device: DeviceWrapper) {
-    let admin = make_admin_test_device(device);
+    let mut admin = make_admin_test_device(device);
     let slot_data = OtpSlotData::new(1, "test-totp", TOTP_SECRET, OtpMode::EightDigits);
-    assert_eq!(Ok(()), admin.write_totp_slot(slot_data, 0));
+    assert_ok!((), admin.write_totp_slot(slot_data, 0));
 
     let device = admin.device();
     let result = device.get_totp_slot_name(1);
-    assert!(result.is_ok());
-    assert_eq!("test-totp", result.unwrap());
+    assert_ok!("test-totp", result);
     let result = device.get_totp_slot_name(16);
-    assert_eq!(CommandError::InvalidSlot, result.unwrap_err());
+    assert_lib_err!(LibraryError::InvalidSlot, result);
 }
 
 #[test_device]
 fn totp_error(device: DeviceWrapper) {
-    let admin = make_admin_test_device(device);
+    let mut admin = make_admin_test_device(device);
     let slot_data = OtpSlotData::new(1, "", TOTP_SECRET, OtpMode::SixDigits);
-    assert_eq!(
-        Err(CommandError::NoName),
-        admin.write_totp_slot(slot_data, 0)
-    );
+    assert_cmd_err!(CommandError::NoName, admin.write_totp_slot(slot_data, 0));
     let slot_data = OtpSlotData::new(20, "test", TOTP_SECRET, OtpMode::SixDigits);
-    assert_eq!(
-        Err(CommandError::InvalidSlot),
+    assert_lib_err!(
+        LibraryError::InvalidSlot,
         admin.write_totp_slot(slot_data, 0)
     );
     let slot_data = OtpSlotData::new(4, "test", "foobar", OtpMode::SixDigits);
-    assert_eq!(
-        Err(CommandError::InvalidHexString),
+    assert_lib_err!(
+        LibraryError::InvalidHexString,
         admin.write_totp_slot(slot_data, 0)
     );
     let code = admin.get_totp_code(20);
-    assert_eq!(CommandError::InvalidSlot, code.unwrap_err());
+    assert_lib_err!(LibraryError::InvalidSlot, code);
 }
 
 #[test_device]
 fn totp_erase(device: DeviceWrapper) {
-    let admin = make_admin_test_device(device);
+    let mut admin = make_admin_test_device(device);
     let config = Config::new(None, None, None, false);
-    assert_eq!(Ok(()), admin.write_config(config));
+    assert_ok!((), admin.write_config(config));
     let slot_data = OtpSlotData::new(1, "test1", TOTP_SECRET, OtpMode::SixDigits);
-    assert_eq!(Ok(()), admin.write_totp_slot(slot_data, 0));
+    assert_ok!((), admin.write_totp_slot(slot_data, 0));
     let slot_data = OtpSlotData::new(2, "test2", TOTP_SECRET, OtpMode::SixDigits);
-    assert_eq!(Ok(()), admin.write_totp_slot(slot_data, 0));
+    assert_ok!((), admin.write_totp_slot(slot_data, 0));
 
-    assert_eq!(Ok(()), admin.erase_totp_slot(1));
+    assert_ok!((), admin.erase_totp_slot(1));
 
     let device = admin.device();
     let result = device.get_totp_slot_name(1);
-    assert_eq!(CommandError::SlotNotProgrammed, result.unwrap_err());
+    assert_cmd_err!(CommandError::SlotNotProgrammed, result);
     let result = device.get_totp_code(1);
-    assert_eq!(CommandError::SlotNotProgrammed, result.unwrap_err());
+    assert_cmd_err!(CommandError::SlotNotProgrammed, result);
 
-    assert_eq!("test2", device.get_totp_slot_name(2).unwrap());
+    assert_ok!("test2".to_string(), device.get_totp_slot_name(2));
 }
diff --git a/tests/pws.rs b/tests/pws.rs
index fbcc0c1..7169695 100644
--- a/tests/pws.rs
+++ b/tests/pws.rs
@@ -1,18 +1,22 @@
+// Copyright (C) 2018-2019 Robin Krahl <robin.krahl@ireas.org>
+// SPDX-License-Identifier: MIT
+
 mod util;
 
 use std::ffi::CStr;
 
 use libc::{c_int, c_void, free};
-use nitrokey::{CommandError, Device, GetPasswordSafe, PasswordSafe, SLOT_COUNT};
+use nitrokey::{
+    CommandError, Device, Error, GetPasswordSafe, LibraryError, PasswordSafe, DEFAULT_ADMIN_PIN,
+    DEFAULT_USER_PIN, SLOT_COUNT,
+};
 use nitrokey_sys;
 use nitrokey_test::test as test_device;
 
-use crate::util::{ADMIN_PASSWORD, USER_PASSWORD};
-
-fn get_slot_name_direct(slot: u8) -> Result<String, CommandError> {
+fn get_slot_name_direct(slot: u8) -> Result<String, Error> {
     let ptr = unsafe { nitrokey_sys::NK_get_password_safe_slot_name(slot) };
     if ptr.is_null() {
-        return Err(CommandError::Undefined);
+        return Err(Error::UnexpectedError);
     }
     let s = unsafe { CStr::from_ptr(ptr).to_string_lossy().into_owned() };
     unsafe { free(ptr as *mut c_void) };
@@ -21,141 +25,135 @@ fn get_slot_name_direct(slot: u8) -> Result<String, CommandError> {
             let error = unsafe { nitrokey_sys::NK_get_last_command_status() } as c_int;
             match error {
                 0 => Ok(s),
-                other => Err(CommandError::from(other)),
+                other => Err(Error::from(other)),
             }
         }
         false => Ok(s),
     }
 }
 
-fn get_pws<T>(device: &T) -> PasswordSafe
+fn get_pws<'a, T>(device: &mut T) -> PasswordSafe<'_, 'a>
 where
-    T: Device,
+    T: Device<'a>,
 {
-    device.get_password_safe(USER_PASSWORD).unwrap()
+    unwrap_ok!(device.get_password_safe(DEFAULT_USER_PIN))
 }
 
 #[test_device]
 fn enable(device: DeviceWrapper) {
-    assert!(device
-        .get_password_safe(&(USER_PASSWORD.to_owned() + "123"))
-        .is_err());
-    assert!(device.get_password_safe(USER_PASSWORD).is_ok());
-    assert!(device.get_password_safe(ADMIN_PASSWORD).is_err());
-    assert!(device.get_password_safe(USER_PASSWORD).is_ok());
+    let mut device = device;
+    assert_cmd_err!(
+        CommandError::WrongPassword,
+        device.get_password_safe(&(DEFAULT_USER_PIN.to_owned() + "123"))
+    );
+    assert_any_ok!(device.get_password_safe(DEFAULT_USER_PIN));
+    assert_cmd_err!(
+        CommandError::WrongPassword,
+        device.get_password_safe(DEFAULT_ADMIN_PIN)
+    );
+    assert_any_ok!(device.get_password_safe(DEFAULT_USER_PIN));
 }
 
 #[test_device]
 fn drop(device: DeviceWrapper) {
+    let mut device = device;
     {
-        let pws = get_pws(&device);
-        assert_eq!(Ok(()), pws.write_slot(1, "name", "login", "password"));
-        assert_eq!("name", pws.get_slot_name(1).unwrap());
+        let mut pws = get_pws(&mut device);
+        assert_ok!((), pws.write_slot(1, "name", "login", "password"));
+        assert_ok!("name".to_string(), pws.get_slot_name(1));
         let result = get_slot_name_direct(1);
-        assert_eq!(Ok(String::from("name")), result);
+        assert_ok!(String::from("name"), result);
     }
     let result = get_slot_name_direct(1);
-    assert_eq!(Ok(String::from("name")), result);
-    assert_eq!(Ok(()), device.lock());
+    assert_ok!(String::from("name"), result);
+    assert_ok!((), device.lock());
     let result = get_slot_name_direct(1);
-    assert_eq!(Err(CommandError::NotAuthorized), result);
+    assert_cmd_err!(CommandError::NotAuthorized, result);
 }
 
 #[test_device]
 fn get_status(device: DeviceWrapper) {
-    let pws = get_pws(&device);
+    let mut device = device;
+    let mut pws = get_pws(&mut device);
     for i in 0..SLOT_COUNT {
-        assert_eq!(Ok(()), pws.erase_slot(i), "Could not erase slot {}", i);
+        assert_ok!((), pws.erase_slot(i));
     }
-    let status = pws.get_slot_status().unwrap();
+    let status = unwrap_ok!(pws.get_slot_status());
     assert_eq!(status, [false; SLOT_COUNT as usize]);
 
-    assert_eq!(Ok(()), pws.write_slot(1, "name", "login", "password"));
-    let status = pws.get_slot_status().unwrap();
+    assert_ok!((), pws.write_slot(1, "name", "login", "password"));
+    let status = unwrap_ok!(pws.get_slot_status());
     for i in 0..SLOT_COUNT {
         assert_eq!(i == 1, status[i as usize]);
     }
 
     for i in 0..SLOT_COUNT {
-        assert_eq!(Ok(()), pws.write_slot(i, "name", "login", "password"));
+        assert_ok!((), pws.write_slot(i, "name", "login", "password"));
     }
-    let status = pws.get_slot_status().unwrap();
-    assert_eq!(status, [true; SLOT_COUNT as usize]);
+    assert_ok!([true; SLOT_COUNT as usize], pws.get_slot_status());
 }
 
 #[test_device]
 fn get_data(device: DeviceWrapper) {
-    let pws = get_pws(&device);
-    assert_eq!(Ok(()), pws.write_slot(1, "name", "login", "password"));
-    assert_eq!("name", pws.get_slot_name(1).unwrap());
-    assert_eq!("login", pws.get_slot_login(1).unwrap());
-    assert_eq!("password", pws.get_slot_password(1).unwrap());
-
-    assert_eq!(Ok(()), pws.erase_slot(1));
-    assert_eq!(Err(CommandError::SlotNotProgrammed), pws.get_slot_name(1));
-    assert_eq!(Err(CommandError::SlotNotProgrammed), pws.get_slot_login(1));
-    assert_eq!(
-        Err(CommandError::SlotNotProgrammed),
-        pws.get_slot_password(1)
-    );
+    let mut device = device;
+    let mut pws = get_pws(&mut device);
+    assert_ok!((), pws.write_slot(1, "name", "login", "password"));
+    assert_ok!("name".to_string(), pws.get_slot_name(1));
+    assert_ok!("login".to_string(), pws.get_slot_login(1));
+    assert_ok!("password".to_string(), pws.get_slot_password(1));
+
+    assert_ok!((), pws.erase_slot(1));
+    assert_cmd_err!(CommandError::SlotNotProgrammed, pws.get_slot_name(1));
+    assert_cmd_err!(CommandError::SlotNotProgrammed, pws.get_slot_login(1));
+    assert_cmd_err!(CommandError::SlotNotProgrammed, pws.get_slot_password(1));
 
     let name = "with å";
     let login = "pär@test.com";
     let password = "'i3lJc[09?I:,[u7dWz9";
-    assert_eq!(Ok(()), pws.write_slot(1, name, login, password));
-    assert_eq!(name, pws.get_slot_name(1).unwrap());
-    assert_eq!(login, pws.get_slot_login(1).unwrap());
-    assert_eq!(password, pws.get_slot_password(1).unwrap());
-
-    assert_eq!(
-        Err(CommandError::InvalidSlot),
-        pws.get_slot_name(SLOT_COUNT)
-    );
-    assert_eq!(
-        Err(CommandError::InvalidSlot),
-        pws.get_slot_login(SLOT_COUNT)
-    );
-    assert_eq!(
-        Err(CommandError::InvalidSlot),
-        pws.get_slot_password(SLOT_COUNT)
-    );
+    assert_ok!((), pws.write_slot(1, name, login, password));
+    assert_ok!(name.to_string(), pws.get_slot_name(1));
+    assert_ok!(login.to_string(), pws.get_slot_login(1));
+    assert_ok!(password.to_string(), pws.get_slot_password(1));
+
+    assert_lib_err!(LibraryError::InvalidSlot, pws.get_slot_name(SLOT_COUNT));
+    assert_lib_err!(LibraryError::InvalidSlot, pws.get_slot_login(SLOT_COUNT));
+    assert_lib_err!(LibraryError::InvalidSlot, pws.get_slot_password(SLOT_COUNT));
 }
 
 #[test_device]
 fn write(device: DeviceWrapper) {
-    let pws = get_pws(&device);
+    let mut device = device;
+    let mut pws = get_pws(&mut device);
 
-    assert_eq!(
-        Err(CommandError::InvalidSlot),
+    assert_lib_err!(
+        LibraryError::InvalidSlot,
         pws.write_slot(SLOT_COUNT, "name", "login", "password")
     );
 
-    assert_eq!(Ok(()), pws.write_slot(0, "", "login", "password"));
-    assert_eq!(Err(CommandError::SlotNotProgrammed), pws.get_slot_name(0));
-    assert_eq!(Ok(String::from("login")), pws.get_slot_login(0));
-    assert_eq!(Ok(String::from("password")), pws.get_slot_password(0));
-
-    assert_eq!(Ok(()), pws.write_slot(0, "name", "", "password"));
-    assert_eq!(Ok(String::from("name")), pws.get_slot_name(0));
-    assert_eq!(Err(CommandError::SlotNotProgrammed), pws.get_slot_login(0));
-    assert_eq!(Ok(String::from("password")), pws.get_slot_password(0));
-
-    assert_eq!(Ok(()), pws.write_slot(0, "name", "login", ""));
-    assert_eq!(Ok(String::from("name")), pws.get_slot_name(0));
-    assert_eq!(Ok(String::from("login")), pws.get_slot_login(0));
-    assert_eq!(
-        Err(CommandError::SlotNotProgrammed),
-        pws.get_slot_password(0)
-    );
+    assert_ok!((), pws.write_slot(0, "", "login", "password"));
+    assert_cmd_err!(CommandError::SlotNotProgrammed, pws.get_slot_name(0));
+    assert_ok!(String::from("login"), pws.get_slot_login(0));
+    assert_ok!(String::from("password"), pws.get_slot_password(0));
+
+    assert_ok!((), pws.write_slot(0, "name", "", "password"));
+    assert_ok!(String::from("name"), pws.get_slot_name(0));
+    assert_cmd_err!(CommandError::SlotNotProgrammed, pws.get_slot_login(0));
+    assert_ok!(String::from("password"), pws.get_slot_password(0));
+
+    assert_ok!((), pws.write_slot(0, "name", "login", ""));
+    assert_ok!(String::from("name"), pws.get_slot_name(0));
+    assert_ok!(String::from("login"), pws.get_slot_login(0));
+    assert_cmd_err!(CommandError::SlotNotProgrammed, pws.get_slot_password(0));
 }
 
 #[test_device]
 fn erase(device: DeviceWrapper) {
-    let pws = get_pws(&device);
-    assert_eq!(Err(CommandError::InvalidSlot), pws.erase_slot(SLOT_COUNT));
-
-    assert_eq!(Ok(()), pws.write_slot(0, "name", "login", "password"));
-    assert_eq!(Ok(()), pws.erase_slot(0));
-    assert_eq!(Ok(()), pws.erase_slot(0));
-    assert_eq!(Err(CommandError::SlotNotProgrammed), pws.get_slot_name(0));
+    let mut device = device;
+    let mut pws = get_pws(&mut device);
+    assert_lib_err!(LibraryError::InvalidSlot, pws.erase_slot(SLOT_COUNT));
+
+    assert_ok!((), pws.write_slot(0, "name", "login", "password"));
+    assert_ok!((), pws.erase_slot(0));
+    assert_ok!((), pws.erase_slot(0));
+    assert_cmd_err!(CommandError::SlotNotProgrammed, pws.get_slot_name(0));
 }
diff --git a/tests/util/mod.rs b/tests/util/mod.rs
index cbf6b93..f2b20ec 100644
--- a/tests/util/mod.rs
+++ b/tests/util/mod.rs
@@ -1,2 +1,113 @@
-pub static ADMIN_PASSWORD: &str = "12345678";
-pub static USER_PASSWORD: &str = "123456";
+// Copyright (C) 2018-2019 Robin Krahl <robin.krahl@ireas.org>
+// SPDX-License-Identifier: MIT
+
+#[macro_export]
+macro_rules! unwrap_ok {
+    ($val:expr) => {{
+        match $val {
+            Ok(val) => val,
+            Err(err) => panic!(
+                r#"assertion failed: `(left == right)`
+  left: `Ok(_)`,
+ right: `Err({:?})`"#,
+                err
+            ),
+        }
+    }};
+}
+
+#[macro_export]
+macro_rules! assert_any_ok {
+    ($val:expr) => {{
+        match &$val {
+            Ok(_) => {}
+            Err(err) => panic!(
+                r#"assertion failed: `(left == right)`
+  left: `Ok(_)`,
+ right: `Err({:?})`"#,
+                err
+            ),
+        }
+    }};
+}
+
+#[macro_export]
+macro_rules! assert_ok {
+    ($left:expr, $right:expr) => {{
+        match &$right {
+            Ok(right) => match &$left {
+                left => {
+                    if !(*left == *right) {
+                        panic!(
+                            r#"assertion failed: `(left == right)`
+  left: `{:?}`,
+ right: `{:?}`"#,
+                            left, right
+                        )
+                    }
+                }
+            },
+            Err(right_err) => panic!(
+                r#"assertion failed: `(left == right)`
+  left: `Ok({:?})`,
+ right: `Err({:?})`"#,
+                $left, right_err
+            ),
+        }
+    }};
+}
+
+#[macro_export]
+macro_rules! assert_err {
+    ($err:path, $left:expr, $right:expr) => {
+        match &$right {
+            Err($err(ref right_err)) => match &$left {
+                left_err => {
+                    if !(*left_err == *right_err) {
+                        panic!(
+                            r#"assertion failed: `(left == right)`
+  left: `{:?}`,
+ right: `{:?}`"#,
+                            left_err, right_err
+                        )
+                    }
+                }
+            },
+            Err(ref right_err) => panic!(
+                r#"assertion failed: `(left == right)`
+  left: `{:?}`,
+ right: `{:?}`"#,
+                $err($left),
+                right_err
+            ),
+            Ok(right_ok) => panic!(
+                r#"assertion failed: `(left == right)`
+  left: `Err({:?})`,
+ right: `Ok({:?})`"#,
+                $err($left),
+                right_ok
+            ),
+        }
+    };
+}
+
+#[macro_export]
+macro_rules! assert_cmd_err {
+    ($left:expr, $right:expr) => {
+        assert_err!(::nitrokey::Error::CommandError, $left, $right);
+    };
+}
+
+#[macro_export]
+macro_rules! assert_cmu_err {
+    ($left:expr, $right:expr) => {
+        assert_err!(::nitrokey::Error::CommunicationError, $left, $right);
+    };
+}
+
+#[macro_export]
+macro_rules! assert_lib_err {
+    ($left:expr, $right:expr) => {
+        assert_err!(::nitrokey::Error::LibraryError, $left, $right);
+    };
+}