Add reset_pin_key

src/backend.rs

@@ -284,6 +284,24 @@ impl ExtensionImpl<AuthExtension> for AuthBackend {
                 .save(fs, self.location)?;
                 Ok(reply::SetPin.into())
             }
+            AuthRequest::ResetPinKey(request) => {
+                let app_key = self.get_app_key(client_id, trussed_fs, ctx, rng)?;
+                let key_to_wrap =
+                    keystore.load_key(Secrecy::Secret, Some(Kind::Symmetric(32)), &request.key)?;
+                let key_to_wrap = (&*key_to_wrap.material)
+                    .try_into()
+                    .map_err(|_| Error::ReadFailed)?;
+                PinData::reset_given_key(
+                    request.id,
+                    &request.pin,
+                    request.retries,
+                    rng,
+                    &app_key,
+                    key_to_wrap,
+                )
+                .save(fs, self.location)?;
+                Ok(reply::ResetPinKey.into())
+            }
             AuthRequest::DeletePin(request) => {
                 let path = request.id.path();
                 if fs.exists(&path, self.location) {

src/backend/data.rs

@@ -171,6 +171,39 @@ impl PinData {
         }
     }
 
+    pub fn reset_given_key<R>(
+        id: PinId,
+        pin: &Pin,
+        retries: Option<u8>,
+        rng: &mut R,
+        application_key: &Key,
+        mut key_to_wrap: Key,
+    ) -> Self
+    where
+        R: CryptoRng + RngCore,
+    {
+        use chacha20poly1305::{AeadInPlace, KeyInit};
+        let mut salt = Salt::default();
+        rng.fill_bytes(salt.as_mut());
+        let pin_key = derive_key(id, pin, &salt, application_key);
+        let aead = ChaCha8Poly1305::new((&*pin_key).into());
+        let nonce = Default::default();
+        #[allow(clippy::expect_used)]
+        let tag: [u8; CHACHA_TAG_LEN] = aead
+            .encrypt_in_place_detached(&nonce, &[u8::from(id)], &mut *key_to_wrap)
+            .expect("Wrapping the key should always work, length are acceptable")
+            .into();
+        Self {
+            id,
+            retries: retries.map(From::from),
+            salt,
+            data: KeyOrHash::Key(WrappedKeyData {
+                wrapped_key: key_to_wrap,
+                tag: tag.into(),
+            }),
+        }
+    }
+
     pub fn load<S: Filestore>(fs: &mut S, location: Location, id: PinId) -> Result<Self, Error> {
         let path = id.path();
         if !fs.exists(&path, location) {

src/extension.rs

@@ -7,7 +7,10 @@ pub mod reply;
 pub mod request;
 
 use serde::{Deserialize, Serialize};
-use trussed::serde_extensions::{Extension, ExtensionClient, ExtensionResult};
+use trussed::{
+    serde_extensions::{Extension, ExtensionClient, ExtensionResult},
+    types::KeyId,
+};
 
 use crate::{Pin, PinId};
 
@@ -32,6 +35,7 @@ pub enum AuthRequest {
     CheckPin(request::CheckPin),
     GetPinKey(request::GetPinKey),
     SetPin(request::SetPin),
+    ResetPinKey(request::ResetPinKey),
     ChangePin(request::ChangePin),
     DeletePin(request::DeletePin),
     DeleteAllPins(request::DeleteAllPins),
@@ -45,6 +49,7 @@ pub enum AuthReply {
     CheckPin(reply::CheckPin),
     GetPinKey(reply::GetPinKey),
     SetPin(reply::SetPin),
+    ResetPinKey(reply::ResetPinKey),
     ChangePin(reply::ChangePin),
     DeletePin(reply::DeletePin),
     DeleteAllPins(reply::DeleteAllPins),
@@ -114,6 +119,25 @@ pub trait AuthClient: ExtensionClient<AuthExtension> {
         })
     }
 
+    /// Reset a pin.
+    ///
+    /// Similar to [`set_pin`](AuthClient::set_pin), but allows the key that the pin will unwrap to be configured.
+    /// This allows for example backing up the key for a pin, to be able to restore it from another source.
+    fn reset_set_pin_key<I: Into<PinId>>(
+        &mut self,
+        id: I,
+        pin: Pin,
+        retries: Option<u8>,
+        key: KeyId,
+    ) -> AuthResult<'_, reply::ResetPinKey, Self> {
+        self.extension(request::ResetPinKey {
+            id: id.into(),
+            pin,
+            retries,
+            key,
+        })
+    }
+
     /// Change the given PIN and resets its retry counter.
     ///
     /// The key obtained by [`get_pin_key`](AuthClient::get_pin_key) will stay the same

src/extension/reply.rs

@@ -99,6 +99,26 @@ impl TryFrom<AuthReply> for SetPin {
     }
 }
 
+#[derive(Debug, Deserialize, Serialize)]
+pub struct ResetPinKey;
+
+impl From<ResetPinKey> for AuthReply {
+    fn from(reply: ResetPinKey) -> Self {
+        Self::ResetPinKey(reply)
+    }
+}
+
+impl TryFrom<AuthReply> for ResetPinKey {
+    type Error = Error;
+
+    fn try_from(reply: AuthReply) -> Result<Self> {
+        match reply {
+            AuthReply::ResetPinKey(reply) => Ok(reply),
+            _ => Err(Error::InternalError),
+        }
+    }
+}
+
 #[derive(Debug, Deserialize, Serialize)]
 pub struct ChangePin {
     pub success: bool,

src/extension/request.rs

@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 or MIT
 
 use serde::{Deserialize, Serialize};
+use trussed::types::KeyId;
 
 use super::AuthRequest;
 use crate::{Pin, PinId};
@@ -56,6 +57,21 @@ impl From<SetPin> for AuthRequest {
     }
 }
 
+#[derive(Debug, Deserialize, Serialize)]
+pub struct ResetPinKey {
+    pub id: PinId,
+    pub pin: Pin,
+    pub retries: Option<u8>,
+    /// If true, the PIN can be used to wrap/unwrap an application key
+    pub key: KeyId,
+}
+
+impl From<ResetPinKey> for AuthRequest {
+    fn from(request: ResetPinKey) -> Self {
+        Self::ResetPinKey(request)
+    }
+}
+
 #[derive(Debug, Deserialize, Serialize)]
 pub struct ChangePin {
     pub id: PinId,

tests/backend.rs

@@ -431,6 +431,58 @@ fn pin_key() {
     )
 }
 
+#[test]
+fn reset_pin_key() {
+    run_with_hw_key(
+        BACKENDS,
+        Bytes::from_slice(b"Some HW ikm").unwrap(),
+        |client| {
+            let pin1 = Bytes::from_slice(b"12345678").unwrap();
+            let pin2 = Bytes::from_slice(b"123456").unwrap();
+            let pin3 = Bytes::from_slice(b"1234567890").unwrap();
+
+            syscall!(client.set_pin(Pin::User, pin1.clone(), Some(3), true));
+            assert!(syscall!(client.get_pin_key(Pin::User, pin2.clone()))
+                .result
+                .is_none());
+            assert_eq!(syscall!(client.pin_retries(Pin::User)).retries, Some(2));
+            assert!(!syscall!(client.check_pin(Pin::User, pin2.clone())).success);
+            assert_eq!(syscall!(client.pin_retries(Pin::User)).retries, Some(1));
+            assert!(syscall!(client.check_pin(Pin::User, pin1.clone())).success);
+            let key = syscall!(client.get_pin_key(Pin::User, pin1))
+                .result
+                .unwrap();
+            assert_eq!(syscall!(client.pin_retries(Pin::User)).retries, Some(3));
+            let mac = syscall!(client.sign_hmacsha256(key, b"Some data")).signature;
+
+            syscall!(client.reset_set_pin_key(Pin::User, pin3.clone(), Some(3), key));
+
+            let key2 = syscall!(client.get_pin_key(Pin::User, pin3.clone()))
+                .result
+                .unwrap();
+            let mac2 = syscall!(client.sign_hmacsha256(key2, b"Some data")).signature;
+            assert_eq!(mac, mac2);
+
+            assert!(syscall!(client.change_pin(Pin::User, pin3.clone(), pin2.clone())).success);
+
+            let key3 = syscall!(client.get_pin_key(Pin::User, pin2.clone()))
+                .result
+                .unwrap();
+            let mac3 = syscall!(client.sign_hmacsha256(key3, b"Some data")).signature;
+            assert_eq!(mac, mac3);
+
+            assert!(!syscall!(client.check_pin(Pin::User, pin3.clone())).success);
+            assert!(!syscall!(client.check_pin(Pin::User, pin3.clone())).success);
+            assert!(!syscall!(client.check_pin(Pin::User, pin3)).success);
+            assert!(!syscall!(client.check_pin(Pin::User, pin2.clone())).success);
+            assert!(syscall!(client.get_pin_key(Pin::User, pin2))
+                .result
+                .is_none());
+            assert_eq!(syscall!(client.pin_retries(Pin::User)).retries, Some(0));
+        },
+    )
+}
+
 #[test]
 fn blocked_pin() {
     run(BACKENDS, |client| {