Merge branch 'mutable-references' into next

RFC:
	https://lists.sr.ht/~ireas/nitrokey-rs-dev/%3C20190126174327.tbuyk2s535kfiqm4%40localhost%3E
	https://lists.sr.ht/~ireas/nitrokey-rs-dev/%3C43cc304d-23e8-7f95-2167-ce3f0530b81e%40posteo.net%3E

* mutable-references:
  Store mutable reference to Device in PasswordSafe
  Refactor User and Admin to use a mutable reference
  Require mutable reference if method changes device state
  Add device_mut method to DeviceWrapper
  Implement DerefMut for User and Admin

11 files changed, 346 insertions, 396 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index a9e3065..9227510 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -34,6 +34,14 @@ SPDX-License-Identifier: MIT
 - 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.
+- Let `Admin` and `User` store a mutable reference to the `Device` instead of
+  the `Device` value.
+- Let `PasswordStore` store a mutable reference to the `Device` instead of a
+  non-mutable reference.
 
 # v0.3.4 (2019-01-20)
 - Fix authentication methods that assumed that `char` is signed.
diff --git a/TODO.md b/TODO.md
index 1ff723d..d6a3509 100644
--- a/TODO.md
+++ b/TODO.md
@@ -13,7 +13,6 @@ SPDX-License-Identifier: MIT
 - Clear passwords from memory.
 - Lock password safe in `PasswordSafe::drop()` (see [nitrokey-storage-firmware
   issue 65][]).
-- Disable creation of multiple password safes at the same time.
 - Check timing in Storage tests.
 - Consider restructuring `device::StorageStatus`.
 
diff --git a/src/auth.rs b/src/auth.rs
index 8978f32..573fed3 100644
--- a/src/auth.rs
+++ b/src/auth.rs
@@ -1,7 +1,7 @@
 // Copyright (C) 2018-2019 Robin Krahl <robin.krahl@ireas.org>
 // SPDX-License-Identifier: MIT
 
-use std::ops::Deref;
+use std::ops;
 use std::os::raw::c_char;
 use std::os::raw::c_int;
 
@@ -42,16 +42,10 @@ pub trait Authenticate {
     /// fn perform_other_task(device: &DeviceWrapper) {}
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::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
-    ///     },
+    /// let mut device = nitrokey::connect()?;
+    /// match device.authenticate_user("123456") {
+    ///     Ok(user) => perform_user_task(&user),
+    ///     Err(err) => eprintln!("Could not authenticate as user: {}", err),
     /// };
     /// perform_other_task(&device);
     /// #     Ok(())
@@ -61,9 +55,9 @@ pub trait Authenticate {
     /// [`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, Error)>
+    fn authenticate_user(&mut self, password: &str) -> Result<User<'_, Self>, Error>
     where
-        Self: Device + Sized;
+        Self: Device + std::marker::Sized;
 
     /// Performs admin authentication.  This method consumes the device.  If successful, an
     /// authenticated device is returned.  Otherwise, the current unauthenticated device and the
@@ -88,16 +82,10 @@ pub trait Authenticate {
     /// fn perform_other_task(device: &DeviceWrapper) {}
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
-    /// let device = match device.authenticate_admin("123456") {
-    ///     Ok(admin) => {
-    ///         perform_admin_task(&admin);
-    ///         admin.device()
-    ///     },
-    ///     Err((device, err)) => {
-    ///         eprintln!("Could not authenticate as admin: {}", err);
-    ///         device
-    ///     },
+    /// let mut device = nitrokey::connect()?;
+    /// match device.authenticate_admin("123456") {
+    ///     Ok(admin) => perform_admin_task(&admin),
+    ///     Err(err) => eprintln!("Could not authenticate as admin: {}", err),
     /// };
     /// perform_other_task(&device);
     /// #     Ok(())
@@ -107,13 +95,13 @@ pub trait Authenticate {
     /// [`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, Error)>
+    fn authenticate_admin(&mut self, password: &str) -> Result<Admin<'_, Self>, Error>
     where
-        Self: Device + Sized;
+        Self: Device + std::marker::Sized;
 }
 
-trait AuthenticatedDevice<T> {
-    fn new(device: T, temp_password: Vec<u8>) -> Self;
+trait AuthenticatedDevice<'a, T> {
+    fn new(device: &'a mut T, temp_password: Vec<u8>) -> Self;
 
     fn temp_password_ptr(&self) -> *const c_char;
 }
@@ -128,8 +116,8 @@ trait AuthenticatedDevice<T> {
 /// [`authenticate_admin`]: trait.Authenticate.html#method.authenticate_admin
 /// [`device`]: #method.device
 #[derive(Debug)]
-pub struct User<T: Device> {
-    device: T,
+pub struct User<'a, T: Device> {
+    device: &'a mut T,
     temp_password: Vec<u8>,
 }
 
@@ -143,84 +131,43 @@ pub struct User<T: Device> {
 /// [`authenticate_admin`]: trait.Authenticate.html#method.authenticate_admin
 /// [`device`]: #method.device
 #[derive(Debug)]
-pub struct Admin<T: Device> {
-    device: T,
+pub struct Admin<'a, T: Device> {
+    device: &'a mut T,
     temp_password: Vec<u8>,
 }
 
-fn authenticate<D, A, T>(device: D, password: &str, callback: T) -> Result<A, (D, Error)>
+fn authenticate<'a, D, A, T>(device: &'a mut D, password: &str, callback: T) -> Result<A, Error>
 where
     D: Device,
-    A: AuthenticatedDevice<D>,
+    A: AuthenticatedDevice<'a, D>,
     T: Fn(*const c_char, *const c_char) -> c_int,
 {
-    let temp_password = match generate_password(TEMPORARY_PASSWORD_LENGTH) {
-        Ok(temp_password) => temp_password,
-        Err(err) => return Err((device, err)),
-    };
-    let password = match get_cstring(password) {
-        Ok(password) => password,
-        Err(err) => return Err((device, err)),
-    };
+    let temp_password = generate_password(TEMPORARY_PASSWORD_LENGTH)?;
+    let password = get_cstring(password)?;
     let password_ptr = password.as_ptr();
     let temp_password_ptr = temp_password.as_ptr() as *const c_char;
     match callback(password_ptr, temp_password_ptr) {
         0 => Ok(A::new(device, temp_password)),
-        rv => Err((device, Error::from(rv))),
+        rv => Err(Error::from(rv)),
     }
 }
 
-fn authenticate_user_wrapper<T, C>(
-    device: T,
-    constructor: C,
-    password: &str,
-) -> Result<User<DeviceWrapper>, (DeviceWrapper, Error)>
-where
-    T: Device,
-    C: Fn(T) -> DeviceWrapper,
-{
-    let result = device.authenticate_user(password);
-    match result {
-        Ok(user) => Ok(User::new(constructor(user.device), user.temp_password)),
-        Err((device, err)) => Err((constructor(device), err)),
-    }
-}
-
-fn authenticate_admin_wrapper<T, C>(
-    device: T,
-    constructor: C,
-    password: &str,
-) -> Result<Admin<DeviceWrapper>, (DeviceWrapper, Error)>
-where
-    T: Device,
-    C: Fn(T) -> DeviceWrapper,
-{
-    let result = device.authenticate_admin(password);
-    match result {
-        Ok(user) => Ok(Admin::new(constructor(user.device), user.temp_password)),
-        Err((device, err)) => Err((constructor(device), err)),
-    }
-}
+impl<'a, T: Device> ops::Deref for User<'a, T> {
+    type Target = T;
 
-impl<T: Device> User<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.
-    pub fn device(self) -> T {
+    fn deref(&self) -> &Self::Target {
         self.device
     }
 }
 
-impl<T: Device> Deref for User<T> {
-    type Target = T;
-
-    fn deref(&self) -> &Self::Target {
-        &self.device
+impl<'a, T: Device> ops::DerefMut for User<'a, T> {
+    fn deref_mut(&mut self) -> &mut T {
+        self.device
     }
 }
 
-impl<T: Device> GenerateOtp for User<T> {
-    fn get_hotp_code(&self, slot: u8) -> Result<String, Error> {
+impl<'a, T: Device> 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())
         })
@@ -233,8 +180,8 @@ impl<T: Device> GenerateOtp for User<T> {
     }
 }
 
-impl<T: Device> AuthenticatedDevice<T> for User<T> {
-    fn new(device: T, temp_password: Vec<u8>) -> Self {
+impl<'a, T: Device> AuthenticatedDevice<'a, T> for User<'a, T> {
+    fn new(device: &'a mut T, temp_password: Vec<u8>) -> Self {
         User {
             device,
             temp_password,
@@ -246,22 +193,21 @@ impl<T: Device> AuthenticatedDevice<T> for User<T> {
     }
 }
 
-impl<T: Device> Deref for Admin<T> {
+impl<'a, T: Device> ops::Deref for Admin<'a, T> {
     type Target = T;
 
     fn deref(&self) -> &Self::Target {
-        &self.device
+        self.device
     }
 }
 
-impl<T: Device> Admin<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.
-    pub fn device(self) -> T {
+impl<'a, T: Device> ops::DerefMut for Admin<'a, T> {
+    fn deref_mut(&mut self) -> &mut T {
         self.device
     }
+}
 
+impl<'a, T: Device> Admin<'a, T> {
     /// Writes the given configuration to the Nitrokey device.
     ///
     /// # Errors
@@ -275,21 +221,18 @@ impl<T: Device> Admin<T> {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// let config = Config::new(None, None, None, false);
     /// match device.authenticate_admin("12345678") {
-    ///     Ok(admin) => {
-    ///         admin.write_config(config);
-    ///         ()
-    ///     },
-    ///     Err((_, err)) => eprintln!("Could not authenticate as admin: {}", err),
+    ///     Ok(mut admin) => admin.write_config(config)?,
+    ///     Err(err) => eprintln!("Could not authenticate as admin: {}", err),
     /// };
     /// #     Ok(())
     /// # }
     /// ```
     ///
     /// [`InvalidSlot`]: enum.LibraryError.html#variant.InvalidSlot
-    pub fn write_config(&self, config: Config) -> Result<(), Error> {
+    pub fn write_config(&mut self, config: Config) -> Result<(), Error> {
         let raw_config = RawConfig::try_from(config)?;
         get_command_result(unsafe {
             nitrokey_sys::NK_write_config(
@@ -304,8 +247,8 @@ impl<T: Device> Admin<T> {
     }
 }
 
-impl<T: Device> ConfigureOtp for Admin<T> {
-    fn write_hotp_slot(&self, data: OtpSlotData, counter: u64) -> Result<(), Error> {
+impl<'a, T: Device> 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(
@@ -322,7 +265,7 @@ impl<T: Device> ConfigureOtp for Admin<T> {
         })
     }
 
-    fn write_totp_slot(&self, data: OtpSlotData, time_window: u16) -> Result<(), Error> {
+    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(
@@ -339,21 +282,21 @@ impl<T: Device> ConfigureOtp for Admin<T> {
         })
     }
 
-    fn erase_hotp_slot(&self, slot: u8) -> Result<(), Error> {
+    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<(), Error> {
+    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> {
-    fn new(device: T, temp_password: Vec<u8>) -> Self {
+impl<'a, T: Device> AuthenticatedDevice<'a, T> for Admin<'a, T> {
+    fn new(device: &'a mut T, temp_password: Vec<u8>) -> Self {
         Admin {
             device,
             temp_password,
@@ -366,35 +309,27 @@ impl<T: Device> AuthenticatedDevice<T> for Admin<T> {
 }
 
 impl Authenticate for DeviceWrapper {
-    fn authenticate_user(self, password: &str) -> Result<User<Self>, (Self, Error)> {
-        match self {
-            DeviceWrapper::Storage(storage) => {
-                authenticate_user_wrapper(storage, DeviceWrapper::Storage, password)
-            }
-            DeviceWrapper::Pro(pro) => authenticate_user_wrapper(pro, DeviceWrapper::Pro, password),
-        }
+    fn authenticate_user(&mut self, password: &str) -> Result<User<'_, 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, Error)> {
-        match self {
-            DeviceWrapper::Storage(storage) => {
-                authenticate_admin_wrapper(storage, DeviceWrapper::Storage, password)
-            }
-            DeviceWrapper::Pro(pro) => {
-                authenticate_admin_wrapper(pro, DeviceWrapper::Pro, password)
-            }
-        }
+    fn authenticate_admin(&mut self, password: &str) -> Result<Admin<'_, Self>, Error> {
+        authenticate(self, password, |password_ptr, temp_password_ptr| unsafe {
+            nitrokey_sys::NK_user_authenticate(password_ptr, temp_password_ptr)
+        })
     }
 }
 
 impl Authenticate for Pro {
-    fn authenticate_user(self, password: &str) -> Result<User<Self>, (Self, Error)> {
+    fn authenticate_user(&mut self, password: &str) -> Result<User<'_, 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, Error)> {
+    fn authenticate_admin(&mut self, password: &str) -> Result<Admin<'_, Self>, Error> {
         authenticate(self, password, |password_ptr, temp_password_ptr| unsafe {
             nitrokey_sys::NK_first_authenticate(password_ptr, temp_password_ptr)
         })
@@ -402,13 +337,13 @@ impl Authenticate for Pro {
 }
 
 impl Authenticate for Storage {
-    fn authenticate_user(self, password: &str) -> Result<User<Self>, (Self, Error)> {
+    fn authenticate_user(&mut self, password: &str) -> Result<User<'_, 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, Error)> {
+    fn authenticate_admin(&mut self, password: &str) -> Result<Admin<'_, 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/device.rs b/src/device.rs
index c985802..a0df30e 100644
--- a/src/device.rs
+++ b/src/device.rs
@@ -71,16 +71,10 @@ impl fmt::Display for VolumeMode {
 /// fn perform_other_task(device: &DeviceWrapper) {}
 ///
 /// # fn try_main() -> Result<(), Error> {
-/// let device = nitrokey::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
-///     },
+/// let mut device = nitrokey::connect()?;
+/// match device.authenticate_user("123456") {
+///     Ok(user) => perform_user_task(&user),
+///     Err(err) => eprintln!("Could not authenticate as user: {}", err),
 /// };
 /// perform_other_task(&device);
 /// #     Ok(())
@@ -135,16 +129,10 @@ pub enum DeviceWrapper {
 /// fn perform_other_task(device: &Pro) {}
 ///
 /// # fn try_main() -> Result<(), Error> {
-/// let device = nitrokey::Pro::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
-///     },
+/// let mut device = nitrokey::Pro::connect()?;
+/// match device.authenticate_user("123456") {
+///     Ok(user) => perform_user_task(&user),
+///     Err(err) => eprintln!("Could not authenticate as user: {}", err),
 /// };
 /// perform_other_task(&device);
 /// #     Ok(())
@@ -181,16 +169,10 @@ pub struct Pro {
 /// fn perform_other_task(device: &Storage) {}
 ///
 /// # fn try_main() -> Result<(), Error> {
-/// let device = nitrokey::Storage::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
-///     },
+/// let mut device = nitrokey::Storage::connect()?;
+/// match device.authenticate_user("123456") {
+///     Ok(user) => perform_user_task(&user),
+///     Err(err) => eprintln!("Could not authenticate as user: {}", err),
 /// };
 /// perform_other_task(&device);
 /// #     Ok(())
@@ -452,7 +434,7 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// match device.change_admin_pin("12345678", "12345679") {
     ///     Ok(()) => println!("Updated admin PIN."),
     ///     Err(err) => eprintln!("Failed to update admin PIN: {}", err),
@@ -463,7 +445,7 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
     ///
     /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    fn change_admin_pin(&self, current: &str, new: &str) -> Result<(), Error> {
+    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 {
@@ -485,7 +467,7 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// match device.change_user_pin("123456", "123457") {
     ///     Ok(()) => println!("Updated admin PIN."),
     ///     Err(err) => eprintln!("Failed to update admin PIN: {}", err),
@@ -496,7 +478,7 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
     ///
     /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    fn change_user_pin(&self, current: &str, new: &str) -> Result<(), Error> {
+    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 {
@@ -518,7 +500,7 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// match device.unlock_user_pin("12345678", "123456") {
     ///     Ok(()) => println!("Unlocked user PIN."),
     ///     Err(err) => eprintln!("Failed to unlock user PIN: {}", err),
@@ -529,7 +511,7 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
     ///
     /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    fn unlock_user_pin(&self, admin_pin: &str, user_pin: &str) -> Result<(), Error> {
+    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 {
@@ -552,7 +534,7 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// match device.lock() {
     ///     Ok(()) => println!("Locked the Nitrokey device."),
     ///     Err(err) => eprintln!("Could not lock the Nitrokey device: {}", err),
@@ -560,7 +542,7 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
     /// #     Ok(())
     /// # }
     /// ```
-    fn lock(&self) -> Result<(), Error> {
+    fn lock(&mut self) -> Result<(), Error> {
         get_command_result(unsafe { nitrokey_sys::NK_lock_device() })
     }
 
@@ -583,7 +565,7 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// match device.factory_reset("12345678") {
     ///     Ok(()) => println!("Performed a factory reset."),
     ///     Err(err) => eprintln!("Could not perform a factory reset: {}", err),
@@ -593,7 +575,7 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
     /// ```
     ///
     /// [`build_aes_key`]: #method.build_aes_key
-    fn factory_reset(&self, admin_pin: &str) -> Result<(), Error> {
+    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()) })
     }
@@ -617,7 +599,7 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::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),
@@ -627,7 +609,7 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
     /// ```
     ///
     /// [`factory_reset`]: #method.factory_reset
-    fn build_aes_key(&self, admin_pin: &str) -> Result<(), Error> {
+    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()) })
     }
@@ -728,6 +710,13 @@ impl DeviceWrapper {
             DeviceWrapper::Pro(ref pro) => pro,
         }
     }
+
+    fn device_mut(&mut self) -> &mut dyn Device {
+        match *self {
+            DeviceWrapper::Storage(ref mut storage) => storage,
+            DeviceWrapper::Pro(ref mut pro) => pro,
+        }
+    }
 }
 
 impl From<Pro> for DeviceWrapper {
@@ -751,8 +740,8 @@ impl GenerateOtp for DeviceWrapper {
         self.device().get_totp_slot_name(slot)
     }
 
-    fn get_hotp_code(&self, slot: u8) -> Result<String, Error> {
-        self.device().get_hotp_code(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> {
@@ -875,7 +864,7 @@ impl Storage {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::Storage::connect()?;
+    /// let mut device = nitrokey::Storage::connect()?;
     /// match device.change_update_pin("12345678", "87654321") {
     ///     Ok(()) => println!("Updated update PIN."),
     ///     Err(err) => eprintln!("Failed to update update PIN: {}", err),
@@ -886,7 +875,7 @@ impl Storage {
     ///
     /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    pub fn change_update_pin(&self, current: &str, new: &str) -> Result<(), Error> {
+    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 {
@@ -912,7 +901,7 @@ impl Storage {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::Storage::connect()?;
+    /// let mut device = nitrokey::Storage::connect()?;
     /// match device.enable_firmware_update("12345678") {
     ///     Ok(()) => println!("Nitrokey entered update mode."),
     ///     Err(err) => eprintln!("Could not enter update mode: {}", err),
@@ -923,7 +912,7 @@ impl Storage {
     ///
     /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    pub fn enable_firmware_update(&self, update_pin: &str) -> Result<(), Error> {
+    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())
@@ -946,7 +935,7 @@ impl Storage {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::Storage::connect()?;
+    /// let mut device = nitrokey::Storage::connect()?;
     /// match device.enable_encrypted_volume("123456") {
     ///     Ok(()) => println!("Enabled the encrypted volume."),
     ///     Err(err) => eprintln!("Could not enable the encrypted volume: {}", err),
@@ -957,7 +946,7 @@ impl Storage {
     ///
     /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    pub fn enable_encrypted_volume(&self, user_pin: &str) -> Result<(), Error> {
+    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()) })
     }
@@ -975,7 +964,7 @@ impl Storage {
     /// fn use_volume() {}
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::Storage::connect()?;
+    /// let mut device = nitrokey::Storage::connect()?;
     /// match device.enable_encrypted_volume("123456") {
     ///     Ok(()) => {
     ///         println!("Enabled the encrypted volume.");
@@ -992,7 +981,7 @@ impl Storage {
     /// #     Ok(())
     /// # }
     /// ```
-    pub fn disable_encrypted_volume(&self) -> Result<(), Error> {
+    pub fn disable_encrypted_volume(&mut self) -> Result<(), Error> {
         get_command_result(unsafe { nitrokey_sys::NK_lock_encrypted_volume() })
     }
 
@@ -1021,7 +1010,7 @@ impl Storage {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::Storage::connect()?;
+    /// let mut device = nitrokey::Storage::connect()?;
     /// device.enable_encrypted_volume("123445")?;
     /// match device.enable_hidden_volume("hidden-pw") {
     ///     Ok(()) => println!("Enabled a hidden volume."),
@@ -1034,7 +1023,7 @@ impl Storage {
     /// [`enable_encrypted_volume`]: #method.enable_encrypted_volume
     /// [`AesDecryptionFailed`]: enum.CommandError.html#variant.AesDecryptionFailed
     /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
-    pub fn enable_hidden_volume(&self, volume_password: &str) -> Result<(), Error> {
+    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())
@@ -1054,7 +1043,7 @@ impl Storage {
     /// fn use_volume() {}
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::Storage::connect()?;
+    /// let mut device = nitrokey::Storage::connect()?;
     /// device.enable_encrypted_volume("123445")?;
     /// match device.enable_hidden_volume("hidden-pw") {
     ///     Ok(()) => {
@@ -1072,7 +1061,7 @@ impl Storage {
     /// #     Ok(())
     /// # }
     /// ```
-    pub fn disable_hidden_volume(&self) -> Result<(), Error> {
+    pub fn disable_hidden_volume(&mut self) -> Result<(), Error> {
         get_command_result(unsafe { nitrokey_sys::NK_lock_hidden_volume() })
     }
 
@@ -1101,7 +1090,7 @@ impl Storage {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::Storage::connect()?;
+    /// let mut device = nitrokey::Storage::connect()?;
     /// device.enable_encrypted_volume("123445")?;
     /// device.create_hidden_volume(0, 0, 100, "hidden-pw")?;
     /// #     Ok(())
@@ -1111,7 +1100,7 @@ impl Storage {
     /// [`AesDecryptionFailed`]: enum.CommandError.html#variant.AesDecryptionFailed
     /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     pub fn create_hidden_volume(
-        &self,
+        &mut self,
         slot: u8,
         start: u8,
         end: u8,
@@ -1141,7 +1130,7 @@ impl Storage {
     /// use nitrokey::VolumeMode;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::Storage::connect()?;
+    /// let mut device = nitrokey::Storage::connect()?;
     /// 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),
@@ -1153,7 +1142,7 @@ impl Storage {
     /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
     pub fn set_unencrypted_volume_mode(
-        &self,
+        &mut self,
         admin_pin: &str,
         mode: VolumeMode,
     ) -> Result<(), Error> {
@@ -1186,7 +1175,7 @@ impl Storage {
     /// use nitrokey::VolumeMode;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::Storage::connect()?;
+    /// let mut device = nitrokey::Storage::connect()?;
     /// 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),
@@ -1198,7 +1187,7 @@ impl Storage {
     /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
     pub fn set_encrypted_volume_mode(
-        &self,
+        &mut self,
         admin_pin: &str,
         mode: VolumeMode,
     ) -> Result<(), Error> {
@@ -1315,7 +1304,7 @@ impl Storage {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::Storage::connect()?;
+    /// let mut device = nitrokey::Storage::connect()?;
     /// 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),
@@ -1326,7 +1315,7 @@ impl Storage {
     ///
     /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    pub fn clear_new_sd_card_warning(&self, admin_pin: &str) -> Result<(), Error> {
+    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())
@@ -1334,7 +1323,7 @@ impl Storage {
     }
 
     /// Blinks the red and green LED alternatively and infinitely until the device is reconnected.
-    pub fn wink(&self) -> Result<(), Error> {
+    pub fn wink(&mut self) -> Result<(), Error> {
         get_command_result(unsafe { nitrokey_sys::NK_wink() })
     }
 
@@ -1354,7 +1343,7 @@ impl Storage {
     ///
     /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    pub fn export_firmware(&self, admin_pin: &str) -> Result<(), Error> {
+    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()) })
     }
diff --git a/src/lib.rs b/src/lib.rs
index f7da8e1..d7a8c5e 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -44,16 +44,16 @@
 //! # use nitrokey::Error;
 //!
 //! # fn try_main() -> Result<(), Error> {
-//! let device = nitrokey::connect()?;
+//! let mut device = nitrokey::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) => eprintln!("Could not write slot: {}", err),
 //!         }
 //!     },
-//!     Err((_, err)) => eprintln!("Could not authenticate as admin: {}", err),
+//!     Err(err) => eprintln!("Could not authenticate as admin: {}", err),
 //! }
 //! #     Ok(())
 //! # }
@@ -66,7 +66,7 @@
 //! # use nitrokey::Error;
 //!
 //! # fn try_main() -> Result<(), Error> {
-//! let device = nitrokey::connect()?;
+//! let mut device = nitrokey::connect()?;
 //! match device.get_hotp_code(1) {
 //!     Ok(code) => println!("Generated HOTP code: {}", code),
 //!     Err(err) => eprintln!("Could not generate HOTP code: {}", err),
diff --git a/src/otp.rs b/src/otp.rs
index abaff66..a8dd20b 100644
--- a/src/otp.rs
+++ b/src/otp.rs
@@ -35,16 +35,16 @@ pub trait ConfigureOtp {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::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) => eprintln!("Could not write slot: {}", err),
     ///         }
     ///     },
-    ///     Err((_, err)) => eprintln!("Could not authenticate as admin: {}", err),
+    ///     Err(err) => eprintln!("Could not authenticate as admin: {}", err),
     /// }
     /// #     Ok(())
     /// # }
@@ -53,7 +53,7 @@ pub trait ConfigureOtp {
     /// [`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<(), Error>;
+    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).
@@ -71,16 +71,16 @@ pub trait ConfigureOtp {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::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) => eprintln!("Could not write slot: {}", err),
     ///         }
     ///     },
-    ///     Err((_, err)) => eprintln!("Could not authenticate as admin: {}", err),
+    ///     Err(err) => eprintln!("Could not authenticate as admin: {}", err),
     /// }
     /// #     Ok(())
     /// # }
@@ -89,7 +89,7 @@ pub trait ConfigureOtp {
     /// [`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<(), Error>;
+    fn write_totp_slot(&mut self, data: OtpSlotData, time_window: u16) -> Result<(), Error>;
 
     /// Erases an HOTP slot.
     ///
@@ -104,22 +104,22 @@ pub trait ConfigureOtp {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// match device.authenticate_admin("12345678") {
-    ///     Ok(admin) => {
+    ///     Ok(mut admin) => {
     ///         match admin.erase_hotp_slot(1) {
     ///             Ok(()) => println!("Successfully erased slot."),
     ///             Err(err) => eprintln!("Could not erase slot: {}", err),
     ///         }
     ///     },
-    ///     Err((_, err)) => eprintln!("Could not authenticate as admin: {}", err),
+    ///     Err(err) => eprintln!("Could not authenticate as admin: {}", err),
     /// }
     /// #     Ok(())
     /// # }
     /// ```
     ///
     /// [`InvalidSlot`]: enum.LibraryError.html#variant.InvalidSlot
-    fn erase_hotp_slot(&self, slot: u8) -> Result<(), Error>;
+    fn erase_hotp_slot(&mut self, slot: u8) -> Result<(), Error>;
 
     /// Erases a TOTP slot.
     ///
@@ -134,22 +134,22 @@ pub trait ConfigureOtp {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// match device.authenticate_admin("12345678") {
-    ///     Ok(admin) => {
+    ///     Ok(mut admin) => {
     ///         match admin.erase_totp_slot(1) {
     ///             Ok(()) => println!("Successfully erased slot."),
     ///             Err(err) => eprintln!("Could not erase slot: {}", err),
     ///         }
     ///     },
-    ///     Err((_, err)) => eprintln!("Could not authenticate as admin: {}", err),
+    ///     Err(err) => eprintln!("Could not authenticate as admin: {}", err),
     /// }
     /// #     Ok(())
     /// # }
     /// ```
     ///
     /// [`InvalidSlot`]: enum.LibraryError.html#variant.InvalidSlot
-    fn erase_totp_slot(&self, slot: u8) -> Result<(), Error>;
+    fn erase_totp_slot(&mut self, slot: u8) -> Result<(), Error>;
 }
 
 /// Provides methods to generate OTP codes and to query OTP slots on a Nitrokey
@@ -171,7 +171,7 @@ pub trait GenerateOtp {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// let time = time::SystemTime::now().duration_since(time::UNIX_EPOCH);
     /// match time {
     ///     Ok(time) => device.set_time(time.as_secs(), false)?,
@@ -187,7 +187,7 @@ 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<(), Error> {
+    fn set_time(&mut self, time: u64, force: bool) -> Result<(), Error> {
         let result = if force {
             unsafe { nitrokey_sys::NK_totp_set_time(time) }
         } else {
@@ -270,7 +270,7 @@ pub trait GenerateOtp {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// let code = device.get_hotp_code(1)?;
     /// println!("Generated HOTP code on slot 1: {}", code);
     /// #     Ok(())
@@ -281,7 +281,7 @@ pub trait GenerateOtp {
     /// [`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, Error> {
+    fn get_hotp_code(&mut self, slot: u8) -> Result<String, Error> {
         result_from_string(unsafe { nitrokey_sys::NK_get_hotp_code(slot) })
     }
 
@@ -305,7 +305,7 @@ pub trait GenerateOtp {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// let time = time::SystemTime::now().duration_since(time::UNIX_EPOCH);
     /// match time {
     ///     Ok(time) => {
diff --git a/src/pws.rs b/src/pws.rs
index 1e27935..a5b9d33 100644
--- a/src/pws.rs
+++ b/src/pws.rs
@@ -18,8 +18,7 @@ pub const SLOT_COUNT: u8 = 16;
 /// The password safe stores a tuple consisting of a name, a login and a password on a slot.  The
 /// number of available slots is [`SLOT_COUNT`][].  The slots are addressed starting with zero.  To
 /// retrieve a password safe from a Nitrokey device, use the [`get_password_safe`][] method from
-/// the [`GetPasswordSafe`][] trait.  Note that the device must live at least as long as the
-/// password safe.
+/// the [`GetPasswordSafe`][] trait.
 ///
 /// Once the password safe has been unlocked, it can be accessed without a password.  Therefore it
 /// is mandatory to call [`lock`][] on the corresponding device after the password store is used.
@@ -43,9 +42,10 @@ pub const SLOT_COUNT: u8 = 16;
 /// }
 ///
 /// # fn try_main() -> Result<(), Error> {
-/// let device = nitrokey::connect()?;
+/// let mut device = nitrokey::connect()?;
 /// let pws = device.get_password_safe("123456")?;
 /// use_password_safe(&pws);
+/// drop(pws);
 /// device.lock()?;
 /// #     Ok(())
 /// # }
@@ -57,21 +57,17 @@ pub const SLOT_COUNT: u8 = 16;
 /// [`GetPasswordSafe`]: trait.GetPasswordSafe.html
 #[derive(Debug)]
 pub struct PasswordSafe<'a> {
-    _device: &'a dyn Device,
+    device: &'a mut dyn Device,
 }
 
 /// Provides access to a [`PasswordSafe`][].
 ///
-/// The device that implements this trait must always live at least as long as a password safe
-/// retrieved from it.
-///
 /// [`PasswordSafe`]: struct.PasswordSafe.html
 pub trait GetPasswordSafe {
     /// Enables and returns the password safe.
     ///
-    /// The underlying device must always live at least as long as a password safe retrieved from
-    /// it.  It is mandatory to lock the underlying device using [`lock`][] after the password safe
-    /// has been used.  Otherwise, other applications can access the password store without
+    /// It is mandatory to lock the underlying device using [`lock`][] after the password safe has
+    /// been used.  Otherwise, other applications can access the password store without
     /// authentication.
     ///
     /// If this method returns an `AesDecryptionFailed` (Nitrokey Pro) or `Unknown` (Nitrokey
@@ -97,14 +93,14 @@ pub trait GetPasswordSafe {
     /// fn use_password_safe(pws: &PasswordSafe) {}
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// match device.get_password_safe("123456") {
     ///     Ok(pws) => {
     ///         use_password_safe(&pws);
-    ///         device.lock()?;
     ///     },
     ///     Err(err) => eprintln!("Could not open the password safe: {}", err),
     /// };
+    /// device.lock()?;
     /// #     Ok(())
     /// # }
     /// ```
@@ -116,16 +112,21 @@ pub trait GetPasswordSafe {
     /// [`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<'_>, Error>;
+    fn get_password_safe(&mut self, user_pin: &str) -> Result<PasswordSafe<'_>, Error>;
 }
 
 fn get_password_safe<'a>(
-    device: &'a dyn Device,
+    device: &'a mut dyn Device,
     user_pin: &str,
 ) -> Result<PasswordSafe<'a>, Error> {
     let user_pin_string = get_cstring(user_pin)?;
-    get_command_result(unsafe { nitrokey_sys::NK_enable_password_safe(user_pin_string.as_ptr()) })
-        .map(|_| PasswordSafe { _device: device })
+    let result = get_command_result(unsafe {
+        nitrokey_sys::NK_enable_password_safe(user_pin_string.as_ptr())
+    });
+    match result {
+        Ok(()) => Ok(PasswordSafe { device }),
+        Err(err) => Err(err),
+    }
 }
 
 fn get_pws_result(s: String) -> Result<String, Error> {
@@ -148,7 +149,7 @@ impl<'a> PasswordSafe<'a> {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// let pws = device.get_password_safe("123456")?;
     /// pws.get_slot_status()?.iter().enumerate().for_each(|(slot, programmed)| {
     ///     let status = match *programmed {
@@ -193,7 +194,7 @@ impl<'a> PasswordSafe<'a> {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// match device.get_password_safe("123456") {
     ///     Ok(pws) => {
     ///         let name = pws.get_slot_name(0)?;
@@ -230,7 +231,7 @@ impl<'a> PasswordSafe<'a> {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// let pws = device.get_password_safe("123456")?;
     /// let name = pws.get_slot_name(0)?;
     /// let login = pws.get_slot_login(0)?;
@@ -263,7 +264,7 @@ impl<'a> PasswordSafe<'a> {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// let pws = device.get_password_safe("123456")?;
     /// let name = pws.get_slot_name(0)?;
     /// let login = pws.get_slot_login(0)?;
@@ -294,7 +295,7 @@ impl<'a> PasswordSafe<'a> {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// let pws = device.get_password_safe("123456")?;
     /// let name = pws.get_slot_name(0)?;
     /// let login = pws.get_slot_login(0)?;
@@ -307,7 +308,7 @@ impl<'a> PasswordSafe<'a> {
     /// [`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,
@@ -340,8 +341,8 @@ impl<'a> PasswordSafe<'a> {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
-    /// let pws = device.get_password_safe("123456")?;
+    /// let mut device = nitrokey::connect()?;
+    /// let mut pws = device.get_password_safe("123456")?;
     /// match pws.erase_slot(0) {
     ///     Ok(()) => println!("Erased slot 0."),
     ///     Err(err) => eprintln!("Could not erase slot 0: {}", err),
@@ -351,7 +352,7 @@ impl<'a> PasswordSafe<'a> {
     /// ```
     ///
     /// [`InvalidSlot`]: enum.LibraryError.html#variant.InvalidSlot
-    pub fn erase_slot(&self, slot: u8) -> Result<(), Error> {
+    pub fn erase_slot(&mut self, slot: u8) -> Result<(), Error> {
         get_command_result(unsafe { nitrokey_sys::NK_erase_password_safe_slot(slot) })
     }
 }
@@ -364,19 +365,19 @@ impl<'a> Drop for PasswordSafe<'a> {
 }
 
 impl GetPasswordSafe for Pro {
-    fn get_password_safe(&self, user_pin: &str) -> Result<PasswordSafe<'_>, Error> {
+    fn get_password_safe(&mut self, user_pin: &str) -> Result<PasswordSafe<'_>, Error> {
         get_password_safe(self, user_pin)
     }
 }
 
 impl GetPasswordSafe for Storage {
-    fn get_password_safe(&self, user_pin: &str) -> Result<PasswordSafe<'_>, Error> {
+    fn get_password_safe(&mut self, user_pin: &str) -> Result<PasswordSafe<'_>, Error> {
         get_password_safe(self, user_pin)
     }
 }
 
 impl GetPasswordSafe for DeviceWrapper {
-    fn get_password_safe(&self, user_pin: &str) -> Result<PasswordSafe<'_>, Error> {
+    fn get_password_safe(&mut self, user_pin: &str) -> Result<PasswordSafe<'_>, Error> {
         get_password_safe(self, user_pin)
     }
 }
diff --git a/tests/device.rs b/tests/device.rs
index 969a7df..bffd767 100644
--- a/tests/device.rs
+++ b/tests/device.rs
@@ -98,42 +98,35 @@ fn get_firmware_version(device: Pro) {
     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));
-    let device = match result {
-        Ok(admin) => admin.device(),
-        Err((device, _)) => device,
-    };
+fn admin_retry<T: Authenticate + Device>(device: &mut T, suffix: &str, count: u8) {
+    assert_any_ok!(device.authenticate_admin(&(ADMIN_PASSWORD.to_owned() + suffix)));
     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));
-    let device = match result {
-        Ok(admin) => admin.device(),
-        Err((device, _)) => device,
-    };
+fn user_retry<T: Authenticate + Device>(device: &mut T, suffix: &str, count: u8) {
+    assert_any_ok!(device.authenticate_user(&(USER_PASSWORD.to_owned() + suffix)));
     assert_ok!(count, device.get_user_retry_count());
-    return device;
 }
 
 #[test_device]
 fn get_retry_count(device: DeviceWrapper) {
-    let device = admin_retry(device, "", 3);
-    let device = admin_retry(device, "123", 2);
-    let device = admin_retry(device, "456", 1);
-    let device = admin_retry(device, "", 3);
-
-    let device = user_retry(device, "", 3);
-    let device = user_retry(device, "123", 2);
-    let device = user_retry(device, "456", 1);
-    user_retry(device, "", 3);
+    let mut device = device;
+
+    admin_retry(&mut device, "", 3);
+    admin_retry(&mut device, "123", 2);
+    admin_retry(&mut device, "456", 1);
+    admin_retry(&mut device, "", 3);
+
+    user_retry(&mut device, "", 3);
+    user_retry(&mut device, "123", 2);
+    user_retry(&mut device, "456", 1);
+    user_retry(&mut device, "", 3);
 }
 
 #[test_device]
 fn config(device: DeviceWrapper) {
-    let admin = unwrap_ok!(device.authenticate_admin(ADMIN_PASSWORD));
+    let mut device = device;
+    let mut admin = unwrap_ok!(device.authenticate_admin(ADMIN_PASSWORD));
 
     let config = Config::new(None, None, None, true);
     assert_ok!((), admin.write_config(config));
@@ -153,41 +146,52 @@ fn config(device: DeviceWrapper) {
 
 #[test_device]
 fn change_user_pin(device: DeviceWrapper) {
-    let device = device.authenticate_user(USER_PASSWORD).unwrap().device();
-    let device = device.authenticate_user(USER_NEW_PASSWORD).unwrap_err().0;
+    let mut device = device;
+    assert_any_ok!(device.authenticate_user(USER_PASSWORD));
+    assert_cmd_err!(
+        CommandError::WrongPassword,
+        device.authenticate_user(USER_NEW_PASSWORD)
+    );
 
     assert_ok!((), device.change_user_pin(USER_PASSWORD, USER_NEW_PASSWORD));
 
-    let device = device.authenticate_user(USER_PASSWORD).unwrap_err().0;
-    let device = device
-        .authenticate_user(USER_NEW_PASSWORD)
-        .unwrap()
-        .device();
+    assert_cmd_err!(
+        CommandError::WrongPassword,
+        device.authenticate_user(USER_PASSWORD)
+    );
+    assert_any_ok!(device.authenticate_user(USER_NEW_PASSWORD));
 
     let result = device.change_user_pin(USER_PASSWORD, USER_PASSWORD);
     assert_cmd_err!(CommandError::WrongPassword, result);
 
     assert_ok!((), device.change_user_pin(USER_NEW_PASSWORD, USER_PASSWORD));
 
-    let device = device.authenticate_user(USER_PASSWORD).unwrap().device();
-    assert!(device.authenticate_user(USER_NEW_PASSWORD).is_err());
+    assert_any_ok!(device.authenticate_user(USER_PASSWORD));
+    assert_cmd_err!(
+        CommandError::WrongPassword,
+        device.authenticate_user(USER_NEW_PASSWORD)
+    );
 }
 
 #[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 mut device = device;
+    assert_any_ok!(device.authenticate_admin(ADMIN_PASSWORD));
+    assert_cmd_err!(
+        CommandError::WrongPassword,
+        device.authenticate_admin(ADMIN_NEW_PASSWORD)
+    );
 
     assert_ok!(
         (),
         device.change_admin_pin(ADMIN_PASSWORD, ADMIN_NEW_PASSWORD)
     );
 
-    let device = device.authenticate_admin(ADMIN_PASSWORD).unwrap_err().0;
-    let device = device
-        .authenticate_admin(ADMIN_NEW_PASSWORD)
-        .unwrap()
-        .device();
+    assert_cmd_err!(
+        CommandError::WrongPassword,
+        device.authenticate_admin(ADMIN_PASSWORD)
+    );
+    assert_any_ok!(device.authenticate_admin(ADMIN_NEW_PASSWORD));
 
     assert_cmd_err!(
         CommandError::WrongPassword,
@@ -199,28 +203,24 @@ fn change_admin_pin(device: DeviceWrapper) {
         device.change_admin_pin(ADMIN_NEW_PASSWORD, ADMIN_PASSWORD)
     );
 
-    let device = device.authenticate_admin(ADMIN_PASSWORD).unwrap().device();
-    device.authenticate_admin(ADMIN_NEW_PASSWORD).unwrap_err();
+    assert_any_ok!(device.authenticate_admin(ADMIN_PASSWORD));
+    assert_cmd_err!(
+        CommandError::WrongPassword,
+        device.authenticate_admin(ADMIN_NEW_PASSWORD)
+    );
 }
 
-fn require_failed_user_login<D>(device: D, password: &str, error: CommandError) -> D
-where
-    D: Device + Authenticate,
-    nitrokey::User<D>: std::fmt::Debug,
-{
-    let result = device.authenticate_user(password);
-    assert!(result.is_err());
-    let err = result.unwrap_err();
-    match err.1 {
-        Error::CommandError(err) => assert_eq!(error, err),
-        _ => assert!(false),
-    };
-    err.0
+fn require_failed_user_login<D: Authenticate + Device>(device: &mut D, password: &str) {
+    assert_cmd_err!(
+        CommandError::WrongPassword,
+        device.authenticate_user(password)
+    );
 }
 
 #[test_device]
 fn unlock_user_pin(device: DeviceWrapper) {
-    let device = device.authenticate_user(USER_PASSWORD).unwrap().device();
+    let mut device = device;
+    assert_any_ok!(device.authenticate_user(USER_PASSWORD));
     assert_ok!((), device.unlock_user_pin(ADMIN_PASSWORD, USER_PASSWORD));
     assert_cmd_err!(
         CommandError::WrongPassword,
@@ -229,10 +229,10 @@ fn unlock_user_pin(device: DeviceWrapper) {
 
     // block user PIN
     let wrong_password = USER_PASSWORD.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);
+    require_failed_user_login(&mut device, &wrong_password);
+    require_failed_user_login(&mut device, &wrong_password);
+    require_failed_user_login(&mut device, &wrong_password);
+    require_failed_user_login(&mut device, USER_PASSWORD);
 
     // unblock with current PIN
     assert_cmd_err!(
@@ -240,13 +240,13 @@ fn unlock_user_pin(device: DeviceWrapper) {
         device.unlock_user_pin(USER_PASSWORD, USER_PASSWORD)
     );
     assert_ok!((), device.unlock_user_pin(ADMIN_PASSWORD, USER_PASSWORD));
-    let device = device.authenticate_user(USER_PASSWORD).unwrap().device();
+    assert_any_ok!(device.authenticate_user(USER_PASSWORD));
 
     // 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);
+    require_failed_user_login(&mut device, &wrong_password);
+    require_failed_user_login(&mut device, &wrong_password);
+    require_failed_user_login(&mut device, &wrong_password);
+    require_failed_user_login(&mut device, USER_PASSWORD);
 
     // unblock with new PIN
     assert_cmd_err!(
@@ -272,12 +272,12 @@ fn assert_utf8_err_or_ne(left: &str, right: Result<String, Error>) {
 
 #[test_device]
 fn factory_reset(device: DeviceWrapper) {
-    let admin = unwrap_ok!(device.authenticate_admin(ADMIN_PASSWORD));
+    let mut device = device;
+    let mut admin = unwrap_ok!(device.authenticate_admin(ADMIN_PASSWORD));
     let otp_data = OtpSlotData::new(1, "test", "0123468790", OtpMode::SixDigits);
     assert_ok!((), admin.write_totp_slot(otp_data, 30));
 
-    let device = admin.device();
-    let pws = unwrap_ok!(device.get_password_safe(USER_PASSWORD));
+    let mut pws = unwrap_ok!(device.get_password_safe(USER_PASSWORD));
     assert_ok!((), pws.write_slot(0, "test", "testlogin", "testpw"));
     drop(pws);
 
@@ -297,23 +297,24 @@ fn factory_reset(device: DeviceWrapper) {
     );
     assert_ok!((), device.factory_reset(ADMIN_NEW_PASSWORD));
 
-    let device = device.authenticate_admin(ADMIN_PASSWORD).unwrap().device();
+    assert_any_ok!(device.authenticate_admin(ADMIN_PASSWORD));
 
     let user = unwrap_ok!(device.authenticate_user(USER_PASSWORD));
     assert_cmd_err!(CommandError::SlotNotProgrammed, user.get_totp_slot_name(1));
 
-    let device = user.device();
     let pws = unwrap_ok!(device.get_password_safe(USER_PASSWORD));
     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_ok!((), device.build_aes_key(ADMIN_PASSWORD));
 }
 
 #[test_device]
 fn build_aes_key(device: DeviceWrapper) {
-    let pws = unwrap_ok!(device.get_password_safe(USER_PASSWORD));
+    let mut device = device;
+    let mut pws = unwrap_ok!(device.get_password_safe(USER_PASSWORD));
     assert_ok!((), pws.write_slot(0, "test", "testlogin", "testpw"));
     drop(pws);
 
@@ -323,7 +324,7 @@ fn build_aes_key(device: DeviceWrapper) {
     );
     assert_ok!((), device.build_aes_key(ADMIN_PASSWORD));
 
-    let device = device.authenticate_admin(ADMIN_PASSWORD).unwrap().device();
+    assert_any_ok!(device.authenticate_admin(ADMIN_PASSWORD));
 
     let pws = unwrap_ok!(device.get_password_safe(USER_PASSWORD));
     assert_utf8_err_or_ne("test", pws.get_slot_name(0));
@@ -333,6 +334,7 @@ fn build_aes_key(device: DeviceWrapper) {
 
 #[test_device]
 fn change_update_pin(device: Storage) {
+    let mut device = device;
     assert_cmd_err!(
         CommandError::WrongPassword,
         device.change_update_pin(UPDATE_NEW_PIN, UPDATE_PIN)
@@ -343,6 +345,7 @@ fn change_update_pin(device: Storage) {
 
 #[test_device]
 fn encrypted_volume(device: Storage) {
+    let mut device = device;
     assert_ok!((), device.lock());
 
     assert_eq!(1, count_nitrokey_block_devices());
@@ -361,6 +364,7 @@ fn encrypted_volume(device: Storage) {
 
 #[test_device]
 fn hidden_volume(device: Storage) {
+    let mut device = device;
     assert_ok!((), device.lock());
 
     assert_eq!(1, count_nitrokey_block_devices());
@@ -396,6 +400,7 @@ fn hidden_volume(device: Storage) {
 
 #[test_device]
 fn lock(device: Storage) {
+    let mut device = device;
     assert_ok!((), device.enable_encrypted_volume(USER_PASSWORD));
     assert_ok!((), device.lock());
     assert_eq!(1, count_nitrokey_block_devices());
@@ -405,6 +410,7 @@ fn lock(device: Storage) {
 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!(
         (),
@@ -441,12 +447,13 @@ fn set_unencrypted_volume_mode(device: Storage) {
         );
     }
 
-    fn assert_success(device: &Storage, mode: VolumeMode) {
+    fn assert_success(device: &mut Storage, mode: VolumeMode) {
         assert_ok!((), device.set_unencrypted_volume_mode(ADMIN_PASSWORD, mode));
         assert_mode(&device, mode);
     }
 
-    assert_success(&device, VolumeMode::ReadOnly);
+    let mut device = device;
+    assert_success(&mut device, VolumeMode::ReadOnly);
 
     assert_cmd_err!(
         CommandError::WrongPassword,
@@ -454,9 +461,9 @@ fn set_unencrypted_volume_mode(device: Storage) {
     );
     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]
@@ -488,6 +495,7 @@ fn get_production_info(device: Storage) {
 
 #[test_device]
 fn clear_new_sd_card_warning(device: Storage) {
+    let mut device = device;
     assert_ok!((), device.factory_reset(ADMIN_PASSWORD));
     thread::sleep(time::Duration::from_secs(3));
     assert_ok!((), device.build_aes_key(ADMIN_PASSWORD));
@@ -506,6 +514,7 @@ fn clear_new_sd_card_warning(device: Storage) {
 
 #[test_device]
 fn export_firmware(device: Storage) {
+    let mut device = device;
     assert_cmd_err!(
         CommandError::WrongPassword,
         device.export_firmware("someadminpn")
diff --git a/tests/otp.rs b/tests/otp.rs
index fc0e79e..8ca8311 100644
--- a/tests/otp.rs
+++ b/tests/otp.rs
@@ -3,8 +3,7 @@
 
 mod util;
 
-use std::fmt::Debug;
-use std::ops::Deref;
+use std::ops::DerefMut;
 
 use nitrokey::{
     Admin, Authenticate, CommandError, Config, ConfigureOtp, Device, GenerateOtp, LibraryError,
@@ -38,22 +37,19 @@ enum TotpTimestampSize {
     U64,
 }
 
-fn make_admin_test_device<T>(device: T) -> Admin<T>
+fn make_admin_test_device<'a, T>(device: &'a mut T) -> Admin<'a, T>
 where
     T: Device,
-    (T, nitrokey::Error): Debug,
 {
-    device
-        .authenticate_admin(ADMIN_PASSWORD)
-        .expect("Could not login as admin.")
+    unwrap_ok!(device.authenticate_admin(ADMIN_PASSWORD))
 }
 
-fn configure_hotp(admin: &ConfigureOtp, counter: u8) {
+fn configure_hotp(admin: &mut ConfigureOtp, counter: u8) {
     let slot_data = OtpSlotData::new(1, "test-hotp", HOTP_SECRET, OtpMode::SixDigits);
     assert_ok!((), admin.write_hotp_slot(slot_data, counter.into()));
 }
 
-fn check_hotp_codes(device: &GenerateOtp, offset: u8) {
+fn check_hotp_codes(device: &mut GenerateOtp, offset: u8) {
     HOTP_CODES.iter().enumerate().for_each(|(i, code)| {
         if i >= offset as usize {
             assert_ok!(code.to_string(), device.get_hotp_code(1));
@@ -63,6 +59,7 @@ fn check_hotp_codes(device: &GenerateOtp, offset: u8) {
 
 #[test_device]
 fn set_time(device: DeviceWrapper) {
+    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));
@@ -71,47 +68,50 @@ fn set_time(device: DeviceWrapper) {
 
 #[test_device]
 fn hotp_no_pin(device: DeviceWrapper) {
-    let admin = make_admin_test_device(device);
+    let mut device = device;
+    let mut admin = make_admin_test_device(&mut device);
     let config = Config::new(None, None, None, false);
     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 device, 0);
 }
 
 #[test_device]
 fn hotp_pin(device: DeviceWrapper) {
-    let admin = make_admin_test_device(device);
+    let mut device = device;
+    let mut admin = make_admin_test_device(&mut device);
     let config = Config::new(None, None, None, true);
     assert_ok!((), admin.write_config(config));
 
-    configure_hotp(&admin, 0);
-    let user = unwrap_ok!(admin.device().authenticate_user(USER_PASSWORD));
-    check_hotp_codes(&user, 0);
+    configure_hotp(&mut admin, 0);
+    let mut user = unwrap_ok!(device.authenticate_user(USER_PASSWORD));
+    check_hotp_codes(&mut user, 0);
 
-    assert_cmd_err!(CommandError::NotAuthorized, user.device().get_hotp_code(1));
+    assert_cmd_err!(CommandError::NotAuthorized, user.get_hotp_code(1));
 }
 
 #[test_device]
 fn hotp_slot_name(device: DeviceWrapper) {
-    let admin = make_admin_test_device(device);
+    let mut device = device;
+    let mut admin = make_admin_test_device(&mut device);
     let slot_data = OtpSlotData::new(1, "test-hotp", HOTP_SECRET, OtpMode::SixDigits);
     assert_ok!((), admin.write_hotp_slot(slot_data, 0));
 
-    let device = admin.device();
     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 device = device;
+    let mut admin = make_admin_test_device(&mut device);
     let slot_data = OtpSlotData::new(1, "", HOTP_SECRET, OtpMode::SixDigits);
     assert_cmd_err!(CommandError::NoName, admin.write_hotp_slot(slot_data, 0));
     let slot_data = OtpSlotData::new(4, "test", HOTP_SECRET, OtpMode::SixDigits);
@@ -130,7 +130,8 @@ fn hotp_error(device: DeviceWrapper) {
 
 #[test_device]
 fn hotp_erase(device: DeviceWrapper) {
-    let admin = make_admin_test_device(device);
+    let mut device = device;
+    let mut admin = make_admin_test_device(&mut device);
     let config = Config::new(None, None, None, false);
     assert_ok!((), admin.write_config(config));
     let slot_data = OtpSlotData::new(1, "test1", HOTP_SECRET, OtpMode::SixDigits);
@@ -140,7 +141,6 @@ fn hotp_erase(device: DeviceWrapper) {
 
     assert_ok!((), admin.erase_hotp_slot(1));
 
-    let device = admin.device();
     let result = device.get_hotp_slot_name(1);
     assert_cmd_err!(CommandError::SlotNotProgrammed, result);
     let result = device.get_hotp_code(1);
@@ -149,13 +149,13 @@ fn hotp_erase(device: DeviceWrapper) {
     assert_ok!("test2".to_string(), device.get_hotp_slot_name(2));
 }
 
-fn configure_totp(admin: &ConfigureOtp, factor: u64) {
+fn configure_totp(admin: &mut ConfigureOtp, factor: u64) {
     let slot_data = OtpSlotData::new(1, "test-totp", TOTP_SECRET, OtpMode::EightDigits);
     let time_window = 30u64.checked_mul(factor).unwrap();
     assert_ok!((), admin.write_totp_slot(slot_data, time_window as u16));
 }
 
-fn check_totp_codes(device: &GenerateOtp, factor: u64, timestamp_size: TotpTimestampSize) {
+fn check_totp_codes(device: &mut 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;
@@ -177,74 +177,76 @@ fn check_totp_codes(device: &GenerateOtp, factor: u64, timestamp_size: TotpTimes
 
 #[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 device = device;
+    let mut admin = make_admin_test_device(&mut device);
     let config = Config::new(None, None, None, false);
     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 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 device = device;
+    let mut admin = make_admin_test_device(&mut device);
     let config = Config::new(None, None, None, false);
     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 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 device = device;
+    let mut admin = make_admin_test_device(&mut device);
     let config = Config::new(None, None, None, true);
     assert_ok!((), admin.write_config(config));
 
-    configure_totp(&admin, 1);
-    let user = unwrap_ok!(admin.device().authenticate_user(USER_PASSWORD));
-    check_totp_codes(&user, 1, TotpTimestampSize::U32);
+    configure_totp(&mut admin, 1);
+    let mut user = unwrap_ok!(device.authenticate_user(USER_PASSWORD));
+    check_totp_codes(&mut user, 1, TotpTimestampSize::U32);
 
-    assert_cmd_err!(CommandError::NotAuthorized, user.device().get_totp_code(1));
+    assert_cmd_err!(CommandError::NotAuthorized, user.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 device = device;
+    let mut admin = make_admin_test_device(&mut device);
     let config = Config::new(None, None, None, true);
     assert_ok!((), admin.write_config(config));
 
-    configure_totp(&admin, 1);
-    let user = unwrap_ok!(admin.device().authenticate_user(USER_PASSWORD));
-    check_totp_codes(&user, 1, TotpTimestampSize::U64);
+    configure_totp(&mut admin, 1);
+    let mut user = unwrap_ok!(admin.authenticate_user(USER_PASSWORD));
+    check_totp_codes(&mut user, 1, TotpTimestampSize::U64);
 
-    assert_cmd_err!(CommandError::NotAuthorized, user.device().get_totp_code(1));
+    assert_cmd_err!(CommandError::NotAuthorized, device.get_totp_code(1));
 }
 
 #[test_device]
 fn totp_slot_name(device: DeviceWrapper) {
-    let admin = make_admin_test_device(device);
+    let mut device = device;
+    let mut admin = make_admin_test_device(&mut device);
     let slot_data = OtpSlotData::new(1, "test-totp", TOTP_SECRET, OtpMode::EightDigits);
     assert_ok!((), admin.write_totp_slot(slot_data, 0));
 
-    let device = admin.device();
     let result = device.get_totp_slot_name(1);
     assert_ok!("test-totp", result);
     let result = device.get_totp_slot_name(16);
@@ -253,7 +255,8 @@ fn totp_slot_name(device: DeviceWrapper) {
 
 #[test_device]
 fn totp_error(device: DeviceWrapper) {
-    let admin = make_admin_test_device(device);
+    let mut device = device;
+    let mut admin = make_admin_test_device(&mut device);
     let slot_data = OtpSlotData::new(1, "", TOTP_SECRET, OtpMode::SixDigits);
     assert_cmd_err!(CommandError::NoName, admin.write_totp_slot(slot_data, 0));
     let slot_data = OtpSlotData::new(20, "test", TOTP_SECRET, OtpMode::SixDigits);
@@ -272,7 +275,8 @@ fn totp_error(device: DeviceWrapper) {
 
 #[test_device]
 fn totp_erase(device: DeviceWrapper) {
-    let admin = make_admin_test_device(device);
+    let mut device = device;
+    let mut admin = make_admin_test_device(&mut device);
     let config = Config::new(None, None, None, false);
     assert_ok!((), admin.write_config(config));
     let slot_data = OtpSlotData::new(1, "test1", TOTP_SECRET, OtpMode::SixDigits);
@@ -282,7 +286,6 @@ fn totp_erase(device: DeviceWrapper) {
 
     assert_ok!((), admin.erase_totp_slot(1));
 
-    let device = admin.device();
     let result = device.get_totp_slot_name(1);
     assert_cmd_err!(CommandError::SlotNotProgrammed, result);
     let result = device.get_totp_code(1);
diff --git a/tests/pws.rs b/tests/pws.rs
index 32dc8f7..7805803 100644
--- a/tests/pws.rs
+++ b/tests/pws.rs
@@ -33,7 +33,7 @@ fn get_slot_name_direct(slot: u8) -> Result<String, Error> {
     }
 }
 
-fn get_pws<T>(device: &T) -> PasswordSafe
+fn get_pws<T>(device: &mut T) -> PasswordSafe
 where
     T: Device,
 {
@@ -42,6 +42,7 @@ where
 
 #[test_device]
 fn enable(device: DeviceWrapper) {
+    let mut device = device;
     assert_cmd_err!(
         CommandError::WrongPassword,
         device.get_password_safe(&(USER_PASSWORD.to_owned() + "123"))
@@ -56,8 +57,9 @@ fn enable(device: DeviceWrapper) {
 
 #[test_device]
 fn drop(device: DeviceWrapper) {
+    let mut device = device;
     {
-        let pws = get_pws(&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));
         let result = get_slot_name_direct(1);
@@ -72,7 +74,8 @@ fn drop(device: DeviceWrapper) {
 
 #[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_ok!((), pws.erase_slot(i));
     }
@@ -93,7 +96,8 @@ fn get_status(device: DeviceWrapper) {
 
 #[test_device]
 fn get_data(device: DeviceWrapper) {
-    let pws = get_pws(&device);
+    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));
@@ -119,7 +123,8 @@ fn get_data(device: DeviceWrapper) {
 
 #[test_device]
 fn write(device: DeviceWrapper) {
-    let pws = get_pws(&device);
+    let mut device = device;
+    let mut pws = get_pws(&mut device);
 
     assert_lib_err!(
         LibraryError::InvalidSlot,
@@ -144,7 +149,8 @@ fn write(device: DeviceWrapper) {
 
 #[test_device]
 fn erase(device: DeviceWrapper) {
-    let pws = get_pws(&device);
+    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"));
diff --git a/tests/util/mod.rs b/tests/util/mod.rs
index bd207a9..f80372d 100644
--- a/tests/util/mod.rs
+++ b/tests/util/mod.rs
@@ -8,7 +8,7 @@ pub static USER_PASSWORD: &str = "123456";
 
 #[macro_export]
 macro_rules! unwrap_ok {
-    ($val:expr) => {{
+    ($val:expr) => {
         match $val {
             Ok(val) => val,
             Err(err) => panic!(
@@ -18,12 +18,12 @@ macro_rules! unwrap_ok {
                 err
             ),
         }
-    }};
+    };
 }
 
 #[macro_export]
 macro_rules! assert_any_ok {
-    ($val:expr) => {{
+    ($val:expr) => {
         match &$val {
             Ok(_) => {}
             Err(err) => panic!(
@@ -33,12 +33,12 @@ macro_rules! assert_any_ok {
                 err
             ),
         }
-    }};
+    };
 }
 
 #[macro_export]
 macro_rules! assert_ok {
-    ($left:expr, $right:expr) => {{
+    ($left:expr, $right:expr) => {
         match &$right {
             Ok(right) => match &$left {
                 left => {
@@ -59,7 +59,7 @@ macro_rules! assert_ok {
                 $left, right_err
             ),
         }
-    }};
+    };
 }
 
 #[macro_export]