crypto: Add methods to export/import cross signing keys

matrix_sdk_crypto/src/lib.rs

@@ -56,7 +56,7 @@ pub use requests::{
     IncomingResponse, KeysQueryRequest, OutgoingRequest, OutgoingRequests,
     OutgoingVerificationRequest, RoomMessageRequest, ToDeviceRequest,
 };
-pub use store::CryptoStoreError;
+pub use store::{CrossSigningKeyExport, CryptoStoreError, SecretImportError};
 pub use verification::{
     AcceptSettings, CancelInfo, QrVerification, Sas, Verification, VerificationRequest,
 };

matrix_sdk_crypto/src/machine.rs

@@ -38,6 +38,7 @@ use ruma::{
             EncryptedEventContent, EncryptedEventScheme, EncryptedToDeviceEventContent,
         },
         room_key::RoomKeyToDeviceEventContent,
+        secret::request::SecretName,
         AnyMessageEventContent, AnyRoomEvent, AnyToDeviceEvent, SyncMessageEvent, ToDeviceEvent,
     },
     DeviceId, DeviceIdBox, DeviceKeyAlgorithm, EventEncryptionAlgorithm, RoomId, UInt, UserId,
@@ -59,10 +60,10 @@ use crate::{
     session_manager::{GroupSessionManager, SessionManager},
     store::{
         Changes, CryptoStore, DeviceChanges, IdentityChanges, MemoryStore, Result as StoreResult,
-        Store,
+        SecretImportError, Store,
     },
     verification::{Verification, VerificationMachine, VerificationRequest},
-    ToDeviceRequest,
+    CrossSigningKeyExport, ToDeviceRequest,
 };
 
 /// State machine implementation of the Olm/Megolm encryption protocol used for
@@ -1262,6 +1263,38 @@ impl OlmMachine {
     pub async fn cross_signing_status(&self) -> CrossSigningStatus {
         self.user_identity.lock().await.status().await
     }
+
+    /// Export all the private cross signing keys we have.
+    ///
+    /// The export will contain the seed for the ed25519 keys as a unpadded
+    /// base64 encoded string.
+    ///
+    /// This method returns `None` if we don't have any private cross signing
+    /// keys.
+    pub async fn export_cross_signing_keys(&self) -> Option<CrossSigningKeyExport> {
+        let master_key = self.store.export_secret(&SecretName::CrossSigningMasterKey).await;
+        let self_signing_key =
+            self.store.export_secret(&SecretName::CrossSigningSelfSigningKey).await;
+        let user_signing_key =
+            self.store.export_secret(&SecretName::CrossSigningUserSigningKey).await;
+
+        if master_key.is_none() && self_signing_key.is_none() && user_signing_key.is_none() {
+            None
+        } else {
+            Some(CrossSigningKeyExport { master_key, self_signing_key, user_signing_key })
+        }
+    }
+
+    /// Import our private cross signing keys.
+    ///
+    /// The export needs to contain the seed for the ed25519 keys as an unpadded
+    /// base64 encoded string.
+    pub async fn import_cross_signing_keys(
+        &self,
+        export: CrossSigningKeyExport,
+    ) -> Result<CrossSigningStatus, SecretImportError> {
+        self.store.import_cross_signing_keys(export).await
+    }
 }
 
 #[cfg(test)]

matrix_sdk_crypto/src/olm/signing/mod.rs

@@ -164,43 +164,81 @@ impl PrivateCrossSigningIdentity {
         &self,
         public_identity: OwnUserIdentity,
         secret_name: &SecretName,
-        seed: String,
+        seed: &str,
     ) -> Result<(), SecretImportError> {
-        let seed = decode(seed)?;
+        let (master, self_signing, user_signing) = match secret_name {
+            SecretName::CrossSigningMasterKey => (Some(seed), None, None),
+            SecretName::CrossSigningSelfSigningKey => (None, Some(seed), None),
+            SecretName::CrossSigningUserSigningKey => (None, None, Some(seed)),
+            _ => return Ok(()),
+        };
 
-        match secret_name {
-            SecretName::CrossSigningMasterKey => {
-                let master = MasterSigning::from_seed(self.user_id().clone(), seed);
+        self.import_secrets(public_identity, master, self_signing, user_signing).await
+    }
 
-                if public_identity.master_key() == &master.public_key {
-                    *self.master_key.lock().await = Some(master);
-                    Ok(())
-                } else {
-                    Err(SecretImportError::MissmatchedPublicKeys)
-                }
+    pub(crate) async fn import_secrets(
+        &self,
+        public_identity: OwnUserIdentity,
+        master_key: Option<&str>,
+        self_signing_key: Option<&str>,
+        user_signing_key: Option<&str>,
+    ) -> Result<(), SecretImportError> {
+        let master = if let Some(master_key) = master_key {
+            let seed = decode(master_key)?;
+
+            let master = MasterSigning::from_seed(self.user_id().clone(), seed);
+
+            if public_identity.master_key() == &master.public_key {
+                Ok(Some(master))
+                // *self.master_key.lock().await = Some(master);
+            } else {
+                Err(SecretImportError::MissmatchedPublicKeys)
             }
-            SecretName::CrossSigningUserSigningKey => {
-                let subkey = UserSigning::from_seed(self.user_id().clone(), seed);
+        } else {
+            Ok(None)
+        }?;
 
-                if public_identity.user_signing_key() == &subkey.public_key {
-                    *self.user_signing_key.lock().await = Some(subkey);
-                    Ok(())
-                } else {
-                    Err(SecretImportError::MissmatchedPublicKeys)
-                }
-            }
-            SecretName::CrossSigningSelfSigningKey => {
-                let subkey = SelfSigning::from_seed(self.user_id().clone(), seed);
+        let user_signing = if let Some(user_signing_key) = user_signing_key {
+            let seed = decode(user_signing_key)?;
+            let subkey = UserSigning::from_seed(self.user_id().clone(), seed);
 
-                if public_identity.self_signing_key() == &subkey.public_key {
-                    *self.self_signing_key.lock().await = Some(subkey);
-                    Ok(())
-                } else {
-                    Err(SecretImportError::MissmatchedPublicKeys)
-                }
+            if public_identity.user_signing_key() == &subkey.public_key {
+                // *self.user_signing_key.lock().await = Some(subkey);
+                Ok(Some(subkey))
+            } else {
+                Err(SecretImportError::MissmatchedPublicKeys)
             }
-            _ => Ok(()),
+        } else {
+            Ok(None)
+        }?;
+
+        let self_signing = if let Some(self_signing_key) = self_signing_key {
+            let seed = decode(self_signing_key)?;
+            let subkey = SelfSigning::from_seed(self.user_id().clone(), seed);
+
+            if public_identity.self_signing_key() == &subkey.public_key {
+                // *self.self_signing_key.lock().await = Some(subkey);
+                Ok(Some(subkey))
+            } else {
+                Err(SecretImportError::MissmatchedPublicKeys)
+            }
+        } else {
+            Ok(None)
+        }?;
+
+        if let Some(master) = master {
+            *self.master_key.lock().await = Some(master);
         }
+
+        if let Some(self_signing) = self_signing {
+            *self.self_signing_key.lock().await = Some(self_signing);
+        }
+
+        if let Some(user_signing) = user_signing {
+            *self.user_signing_key.lock().await = Some(user_signing);
+        }
+
+        Ok(())
     }
 
     /// Get the names of the secrets we are missing.

matrix_sdk_crypto/src/store/mod.rs

@@ -63,6 +63,7 @@ use ruma::{
 use serde_json::Error as SerdeError;
 use thiserror::Error;
 use tracing::{info, warn};
+use zeroize::Zeroize;
 
 #[cfg(feature = "sled_cryptostore")]
 pub use self::sled::SledStore;
@@ -136,8 +137,33 @@ impl DeviceChanges {
     }
 }
 
+/// A struct containing private cross signing keys that can be backed up or
+/// uploaded to the secret store.
+#[derive(Zeroize)]
+#[zeroize(drop)]
+pub struct CrossSigningKeyExport {
+    /// The seed of the master key encoded as unpadded base64.
+    pub master_key: Option<String>,
+    /// The seed of the self signing key encoded as unpadded base64.
+    pub self_signing_key: Option<String>,
+    /// The seed of the user signing key encoded as unpadded base64.
+    pub user_signing_key: Option<String>,
+}
+
+impl Debug for CrossSigningKeyExport {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("CrossSigningKeyExport")
+            .field("master_key", &self.master_key.is_some())
+            .field("self_signing_key", &self.self_signing_key.is_some())
+            .field("user_signing_key", &self.user_signing_key.is_some())
+            .finish_non_exhaustive()
+    }
+}
+
+/// Error describing what went wrong when importing private cross signing keys
+/// or the key backup key.
 #[derive(Debug, Error)]
-pub(crate) enum SecretImportError {
+pub enum SecretImportError {
     /// The seed for the private key wasn't valid base64.
     #[error(transparent)]
     Base64(#[from] DecodeError),
@@ -367,11 +393,42 @@ impl Store {
         }
     }
 
+    pub async fn import_cross_signing_keys(
+        &self,
+        export: CrossSigningKeyExport,
+    ) -> Result<CrossSigningStatus, SecretImportError> {
+        if let Some(public_identity) = self.get_identity(&self.user_id).await?.and_then(|i| i.own())
+        {
+            let identity = self.identity.lock().await;
+
+            identity
+                .import_secrets(
+                    public_identity,
+                    export.master_key.as_deref(),
+                    export.self_signing_key.as_deref(),
+                    export.user_signing_key.as_deref(),
+                )
+                .await?;
+
+            let status = identity.status().await;
+            info!(status =? status, "Successfully imported the private cross signing keys");
+
+            let changes =
+                Changes { private_identity: Some(identity.clone()), ..Default::default() };
+
+            self.save_changes(changes).await?;
+        }
+
+        Ok(self.identity.lock().await.status().await)
+    }
+
     pub async fn import_secret(
         &self,
         secret_name: &SecretName,
         secret: String,
     ) -> Result<(), SecretImportError> {
+        let secret = zeroize::Zeroizing::new(secret);
+
         match secret_name {
             SecretName::CrossSigningMasterKey
             | SecretName::CrossSigningUserSigningKey
@@ -381,7 +438,7 @@ impl Store {
                 {
                     let identity = self.identity.lock().await;
 
-                    identity.import_secret(public_identity, secret_name, secret).await?;
+                    identity.import_secret(public_identity, secret_name, &secret).await?;
                     info!(
                         secret_name = secret_name.as_ref(),
                         "Successfully imported a private cross signing key"