Add Device::build_aes_key method

This patch adds the build_aes_key method to the Device trait that uses
the NK_build_aes_key function to build new AES keys on the device.  This
effectively resets the password safe and the encrypted storage.  It is
unclear whether other data (e. g. the one-time passwords) are affected
too.

5 files changed, 61 insertions, 1 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8ecaef3..2551350 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,7 @@
 - Add the `Storage::change_update_pin` method that changes the firmware update
   PIN.
 - Add the `Device::factory_reset` method that performs a factory reset.
+- Add the `Device::build_aes_key` method that builds a new AES key on the Nitrokey.
 
 # v0.2.3 (2018-12-31)
 
diff --git a/TODO.md b/TODO.md
index 5bcfa68..9555747 100644
--- a/TODO.md
+++ b/TODO.md
@@ -1,6 +1,5 @@
 - Add support for the currently unsupported commands:
     - `NK_set_unencrypted_volume_rorw_pin_type_user`
-    - `NK_build_aes_key`
     - `NK_is_AES_supported`
     - `NK_send_startup`
     - `NK_unlock_hidden_volume`
diff --git a/src/device.rs b/src/device.rs
index 8702405..bc48cd2 100644
--- a/src/device.rs
+++ b/src/device.rs
@@ -540,6 +540,37 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp {
         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 using `gpg --card-edit`.  You can also use it to
+    /// destory 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(())
+    /// # }
+    /// ```
+    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,
diff --git a/src/pws.rs b/src/pws.rs
index c20ad1d..ebd5fcd 100644
--- a/src/pws.rs
+++ b/src/pws.rs
@@ -71,6 +71,11 @@ pub trait GetPasswordSafe {
     /// has been used.  Otherwise, other applications can access the password store without
     /// authentication.
     ///
+    /// If this method returns an `AesDecryptionFailed` (Nitrokey Pro) or `Unknown` (Nitrokey
+    /// Storage) error, the AES data object on the smart card could not be accessed.  This problem
+    /// occurs after a factory reset using `gpg --card-edit` and can be fixed using the
+    /// [`Device::build_aes_key`][] command.
+    ///
     /// # Errors
     ///
     /// - [`AesDecryptionFailed`][] if the secret for the password safe could not be decrypted
@@ -104,6 +109,7 @@ pub trait GetPasswordSafe {
     /// [`device`]: struct.PasswordSafe.html#method.device
     /// [`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
     /// [`Unknown`]: enum.CommandError.html#variant.Unknown
     /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
diff --git a/tests/device.rs b/tests/device.rs
index 363b8d8..06e014e 100644
--- a/tests/device.rs
+++ b/tests/device.rs
@@ -347,6 +347,29 @@ fn factory_reset() {
 }
 
 #[test]
+#[cfg_attr(not(any(feature = "test-pro", feature = "test-storage")), ignore)]
+fn build_aes_key() {
+    let device = Target::connect().unwrap();
+
+    let pws = device.get_password_safe(USER_PASSWORD).unwrap();
+    assert_eq!(Ok(()), pws.write_slot(0, "test", "testlogin", "testpw"));
+    drop(pws);
+
+    assert_eq!(
+        Err(CommandError::WrongPassword),
+        device.build_aes_key(USER_PASSWORD)
+    );
+    assert_eq!(Ok(()), device.build_aes_key(ADMIN_PASSWORD));
+
+    let device = device.authenticate_admin(ADMIN_PASSWORD).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());
+}
+
+#[test]
 #[cfg_attr(not(feature = "test-storage"), ignore)]
 fn change_update_pin() {
     let device = Storage::connect().unwrap();