crypto: Expose a way to pin a user's identity

bindings/matrix-sdk-ffi/CHANGELOG.md

@@ -31,4 +31,5 @@ Breaking changes:
 
 Additions:
 
+- Add `Encryption::get_user_identity`
 - Add `ClientBuilder::room_key_recipient_strategy`

bindings/matrix-sdk-ffi/src/encryption.rs

@@ -410,6 +410,50 @@ impl Encryption {
     pub async fn wait_for_e2ee_initialization_tasks(&self) {
         self.inner.wait_for_e2ee_initialization_tasks().await;
     }
+
+    /// Get the E2EE identity of a user.
+    ///
+    /// Returns an error if this user does not exist, if there is an error
+    /// contacting the crypto store, or if our client is not logged in.
+    pub async fn get_user_identity(
+        &self,
+        user_id: String,
+    ) -> Result<Arc<UserIdentity>, ClientError> {
+        Ok(Arc::new(UserIdentity {
+            inner: self
+                .inner
+                .get_user_identity(user_id.as_str().try_into()?)
+                .await?
+                .ok_or(ClientError::new("User not found"))?,
+        }))
+    }
+}
+
+/// The E2EE identity of a user.
+#[derive(uniffi::Object)]
+pub struct UserIdentity {
+    inner: matrix_sdk::encryption::identities::UserIdentity,
+}
+
+#[uniffi::export]
+impl UserIdentity {
+    /// Remember this identity, ensuring it does not result in a pin violation.
+    ///
+    /// When we first see a user, we assume their cryptographic identity has not
+    /// been tampered with by the homeserver or another entity with
+    /// man-in-the-middle capabilities. We remember this identity and call this
+    /// action "pinning".
+    ///
+    /// If the identity presented for the user changes later on, the newly
+    /// presented identity is considered to be in "pin violation". This
+    /// method explicitly accepts the new identity, allowing it to replace
+    /// the previously pinned one and bringing it out of pin violation.
+    ///
+    /// UIs should display a warning to the user when encountering an identity
+    /// which is not verified and is in pin violation.
+    pub(crate) async fn pin(&self) -> Result<(), ClientError> {
+        Ok(self.inner.pin().await?)
+    }
 }
 
 #[derive(uniffi::Object)]

crates/matrix-sdk-crypto/src/identities/user.rs

@@ -125,6 +125,32 @@ impl UserIdentity {
         }
     }
 
+    /// Remember this identity, ensuring it does not result in a pin violation.
+    ///
+    /// When we first see a user, we assume their cryptographic identity has not
+    /// been tampered with by the homeserver or another entity with
+    /// man-in-the-middle capabilities. We remember this identity and call this
+    /// action "pinning".
+    ///
+    /// If the identity presented for the user changes later on, the newly
+    /// presented identity is considered to be in "pin violation". This
+    /// method explicitly accepts the new identity, allowing it to replace
+    /// the previously pinned one and bringing it out of pin violation.
+    ///
+    /// UIs should display a warning to the user when encountering an identity
+    /// which is not verified and is in pin violation. See
+    /// [`OtherUserIdentity::identity_needs_user_approval`].
+    pub async fn pin(&self) -> Result<(), CryptoStoreError> {
+        match self {
+            UserIdentity::Own(_) => {
+                // Nothing to be done for our own identity: we already
+                // consider it trusted in this sense.
+                Ok(())
+            }
+            UserIdentity::Other(u) => u.pin_current_master_key().await,
+        }
+    }
+
     /// Was this identity previously verified, and is no longer?
     pub fn has_verification_violation(&self) -> bool {
         match self {
@@ -737,7 +763,21 @@ impl OtherUserIdentityData {
         &self.self_signing_key
     }
 
-    /// Pin the current identity
+    /// Remember this identity, ensuring it does not result in a pin violation.
+    ///
+    /// When we first see a user, we assume their cryptographic identity has not
+    /// been tampered with by the homeserver or another entity with
+    /// man-in-the-middle capabilities. We remember this identity and call this
+    /// action "pinning".
+    ///
+    /// If the identity presented for the user changes later on, the newly
+    /// presented identity is considered to be in "pin violation". This
+    /// method explicitly accepts the new identity, allowing it to replace
+    /// the previously pinned one and bringing it out of pin violation.
+    ///
+    /// UIs should display a warning to the user when encountering an identity
+    /// which is not verified and is in pin violation. See
+    /// [`OtherUserIdentity::identity_needs_user_approval`].
     pub(crate) fn pin(&self) {
         let mut m = self.pinned_master_key.write().unwrap();
         *m = self.master_key.as_ref().clone()

crates/matrix-sdk/CHANGELOG.md

@@ -28,6 +28,7 @@ Breaking changes:
 
 Additions:
 
+- new `UserIdentity::pin` method.
 - new `ClientBuilder::with_decryption_trust_requirement` method.
 - new `ClientBuilder::with_room_key_recipient_strategy` method
 - new `Room.set_account_data` and `Room.set_account_data_raw` RoomAccountData setters, analogous to the GlobalAccountData

crates/matrix-sdk/src/encryption/identities/users.rs

@@ -422,6 +422,24 @@ impl UserIdentity {
         self.inner.withdraw_verification().await
     }
 
+    /// Remember this identity, ensuring it does not result in a pin violation.
+    ///
+    /// When we first see a user, we assume their cryptographic identity has not
+    /// been tampered with by the homeserver or another entity with
+    /// man-in-the-middle capabilities. We remember this identity and call this
+    /// action "pinning".
+    ///
+    /// If the identity presented for the user changes later on, the newly
+    /// presented identity is considered to be in "pin violation". This
+    /// method explicitly accepts the new identity, allowing it to replace
+    /// the previously pinned one and bringing it out of pin violation.
+    ///
+    /// UIs should display a warning to the user when encountering an identity
+    /// which is not verified and is in pin violation.
+    pub async fn pin(&self) -> Result<(), CryptoStoreError> {
+        self.inner.pin().await
+    }
+
     /// Get the public part of the Master key of this user identity.
     ///
     /// The public part of the Master key is usually used to uniquely identify

crates/matrix-sdk/src/room/identity_status_changes.rs

@@ -430,9 +430,10 @@ mod tests {
                     );
 
                     // Pin it
-                    self.crypto_other_identity()
+                    self.user_identity()
                         .await
-                        .pin_current_master_key()
+                        .expect("User should exist")
+                        .pin()
                         .await
                         .expect("Should not fail to pin");
                 } else {