Element-R: implement {get,store}SessionBackupPrivateKey (#3622)

package.json

@@ -55,7 +55,7 @@
     ],
     "dependencies": {
         "@babel/runtime": "^7.12.5",
-        "@matrix-org/matrix-sdk-crypto-wasm": "^1.0.1",
+        "@matrix-org/matrix-sdk-crypto-wasm": "^1.1.0",
         "another-json": "^0.2.0",
         "bs58": "^5.0.0",
         "content-type": "^1.0.4",

spec/unit/rust-crypto/rust-crypto.spec.ts

@@ -503,6 +503,16 @@ describe("RustCrypto", () => {
             );
         });
     });
+
+    describe("get|storeSessionBackupPrivateKey", () => {
+        it("can save and restore a key", async () => {
+            const key = "testtesttesttesttesttesttesttest";
+            const rustCrypto = await makeTestRustCrypto();
+            await rustCrypto.storeSessionBackupPrivateKey(new TextEncoder().encode(key));
+            const fetched = await rustCrypto.getSessionBackupPrivateKey();
+            expect(new TextDecoder().decode(fetched!)).toEqual(key);
+        });
+    });
 });
 
 /** build a basic RustCrypto instance for testing

src/client.ts

@@ -3726,10 +3726,10 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
         backupInfo: IKeyBackupInfo,
         opts?: IKeyBackupRestoreOpts,
     ): Promise<IKeyBackupRestoreResult> {
-        if (!this.crypto) {
+        if (!this.cryptoBackend) {
             throw new Error("End-to-end encryption disabled");
         }
-        const privKey = await this.crypto.getSessionBackupPrivateKey();
+        const privKey = await this.cryptoBackend.getSessionBackupPrivateKey();
         if (!privKey) {
             throw new Error("Couldn't get key");
         }
@@ -3767,7 +3767,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
         const cacheCompleteCallback = opts?.cacheCompleteCallback;
         const progressCallback = opts?.progressCallback;
 
-        if (!this.crypto) {
+        if (!this.cryptoBackend) {
             throw new Error("End-to-end encryption disabled");
         }
 
@@ -3790,9 +3790,13 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
                 return Promise.reject(new MatrixError({ errcode: MatrixClient.RESTORE_BACKUP_ERROR_BAD_KEY }));
             }
 
+            if (!(privKey instanceof Uint8Array)) {
+                // eslint-disable-next-line @typescript-eslint/no-base-to-string
+                throw new Error(`restoreKeyBackup expects Uint8Array, got ${privKey}`);
+            }
             // Cache the key, if possible.
             // This is async.
-            this.crypto
+            this.cryptoBackend
                 .storeSessionBackupPrivateKey(privKey)
                 .catch((e) => {
                     logger.warn("Error caching session backup key:", e);
@@ -3849,7 +3853,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
             algorithm.free();
         }
 
-        await this.getCrypto()?.importRoomKeys(keys, {
+        await this.cryptoBackend.importRoomKeys(keys, {
             progressCallback,
             untrusted,
             source: "backup",

src/crypto-api.ts

@@ -284,6 +284,30 @@ export interface CryptoApi {
      * @returns a VerificationRequest when the request has been sent to the other party.
      */
     requestDeviceVerification(userId: string, deviceId: string): Promise<VerificationRequest>;
+
+    ///////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+    //
+    // Secure key backup
+    //
+    ///////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+
+    /**
+     * Fetch the backup decryption key we have saved in our store.
+     *
+     * This can be used for gossiping the key to other devices.
+     *
+     * @returns the key, if any, or null
+     */
+    getSessionBackupPrivateKey(): Promise<Uint8Array | null>;
+
+    /**
+     * Store the backup decryption key.
+     *
+     * This should be called if the client has received the key from another device via secret sharing (gossiping).
+     *
+     * @param key - the backup decryption key
+     */
+    storeSessionBackupPrivateKey(key: Uint8Array): Promise<void>;
 }
 
 /**

src/rust-crypto/rust-crypto.ts

@@ -698,6 +698,33 @@ export class RustCrypto extends TypedEventEmitter<RustCryptoEvents, RustCryptoEv
         return new RustVerificationRequest(request, this.outgoingRequestProcessor, this._supportedVerificationMethods);
     }
 
+    /**
+     * Fetch the backup decryption key we have saved in our store.
+     *
+     * Implementation of {@link CryptoApi#getSessionBackupPrivateKey}.
+     *
+     * @returns the key, if any, or null
+     */
+    public async getSessionBackupPrivateKey(): Promise<Uint8Array | null> {
+        const backupKeys: RustSdkCryptoJs.BackupKeys = await this.olmMachine.getBackupKeys();
+        if (!backupKeys.decryptionKeyBase64) return null;
+        return Buffer.from(backupKeys.decryptionKeyBase64, "base64");
+    }
+
+    /**
+     * Store the backup decryption key.
+     *
+     * Implementation of {@link CryptoApi#storeSessionBackupPrivateKey}.
+     *
+     * @param key - the backup decryption key
+     */
+    public async storeSessionBackupPrivateKey(key: Uint8Array): Promise<void> {
+        const base64Key = Buffer.from(key).toString("base64");
+
+        // TODO get version from backupManager
+        await this.olmMachine.saveBackupDecryptionKey(RustSdkCryptoJs.BackupDecryptionKey.fromBase64(base64Key), "");
+    }
+
     ///////////////////////////////////////////////////////////////////////////////////////////////////////////////////
     //
     // SyncCryptoCallbacks implementation

yarn.lock

@@ -1482,10 +1482,10 @@
     "@jridgewell/resolve-uri" "3.1.0"
     "@jridgewell/sourcemap-codec" "1.4.14"
 
-"@matrix-org/matrix-sdk-crypto-wasm@^1.0.1":
-  version "1.0.1"
-  resolved "https://registry.yarnpkg.com/@matrix-org/matrix-sdk-crypto-wasm/-/matrix-sdk-crypto-wasm-1.0.1.tgz#21a0557a7bb3f60b37c6d412be8906c056fe79b8"
-  integrity sha512-VTwV5IowvhhLXwAsDDAv02bC5/qBQbG2YtpYAije11253sQ3MePIoSR+dS40Ih3lAlEzqQ00GU3O+i45jMzIRQ==
+"@matrix-org/matrix-sdk-crypto-wasm@^1.1.0":
+  version "1.1.0"
+  resolved "https://registry.yarnpkg.com/@matrix-org/matrix-sdk-crypto-wasm/-/matrix-sdk-crypto-wasm-1.1.0.tgz#43996a2c5fc8786999eeaaf6df51007244f6b3c4"
+  integrity sha512-BSMYqXRgQOHG3N18z8b05x3UQcdLL3XDrxjtjjA88t9PadZ7RwNowLm1Sx3ESzdzRX+r1SEVAWs2JnTTs0rv3Q==
 
 "@matrix-org/olm@https://gitlab.matrix.org/api/v4/projects/27/packages/npm/@matrix-org/olm/-/@matrix-org/olm-3.2.14.tgz":
   version "3.2.14"