integrate session backup with session class

src/matrix/Session.js

@@ -23,12 +23,19 @@ import {Account as E2EEAccount} from "./e2ee/Account.js";
 import {Decryption as OlmDecryption} from "./e2ee/olm/Decryption.js";
 import {Encryption as OlmEncryption} from "./e2ee/olm/Encryption.js";
 import {Decryption as MegOlmDecryption} from "./e2ee/megolm/Decryption.js";
+import {SessionBackup} from "./e2ee/megolm/SessionBackup.js";
 import {Encryption as MegOlmEncryption} from "./e2ee/megolm/Encryption.js";
 import {MEGOLM_ALGORITHM} from "./e2ee/common.js";
 import {RoomEncryption} from "./e2ee/RoomEncryption.js";
 import {DeviceTracker} from "./e2ee/DeviceTracker.js";
 import {LockMap} from "../utils/LockMap.js";
 import {groupBy} from "../utils/groupBy.js";
+import {
+    keyFromCredential as ssssKeyFromCredential,
+    readKey as ssssReadKey,
+    writeKey as ssssWriteKey,
+    SecretStorage
+} from "./ssss/index.js"
 
 const PICKLE_KEY = "DEFAULT_KEY";
 
@@ -54,6 +61,7 @@ export class Session {
         this._megolmDecryption = null;
         this._getSyncToken = () => this.syncToken;
         this._olmWorker = olmWorker;
+        this._cryptoDriver = cryptoDriver;
 
         if (olm) {
             this._olmUtil = new olm.Utility();
@@ -130,10 +138,54 @@ export class Session {
             megolmEncryption: this._megolmEncryption,
             megolmDecryption: this._megolmDecryption,
             storage: this._storage,
-            encryptionParams
+            sessionBackup: this._sessionBackup,
+            encryptionParams,
         });
     }
 
+    /**
+     * Enable secret storage by providing the secret storage credential.
+     * This will also see if there is a megolm session backup and try to enable that if so.
+     * 
+     * @param  {string} type       either "passphrase" or "recoverykey"
+     * @param  {string} credential either the passphrase or the recovery key, depending on the type
+     * @return {Promise} resolves or rejects after having tried to enable secret storage
+     */
+    async enableSecretStorage(type, credential) {
+        if (!this._olm) {
+            throw new Error("olm required");
+        }
+        const key = ssssKeyFromCredential(type, credential, this._storage, this._cryptoDriver);
+        // write the key
+        let txn = await this._storage.readWriteTxn([
+            this._storage.storeNames.session,
+        ]);
+        try {
+            ssssWriteKey(key, txn);
+        } catch (err) {
+            txn.abort();
+            throw err;
+        }
+        await txn.complete();
+        // and create session backup, which needs to read from accountData
+        txn = await this._storage.readTxn([
+            this._storage.storeNames.accountData,
+        ]);
+        await this._createSessionBackup(key, txn);
+    }
+
+    async _createSessionBackup(ssssKey, txn) {
+        const secretStorage = new SecretStorage({key: ssssKey, cryptoDriver: this._cryptoDriver});
+        this._sessionBackup = await SessionBackup.fromSecretStorage({olm: this._olm, secretStorage, hsApi: this._hsApi, txn});
+        if (this._sessionBackup) {
+            for (const room of this._rooms.values()) {
+                if (room.isEncrypted) {
+                    room.enableSessionBackup(this._sessionBackup);
+                }
+            }
+        }
+    }
+
     // called after load
     async beforeFirstSync(isNewLogin) {
         if (this._olm) {
@@ -155,6 +207,17 @@ export class Session {
             await this._e2eeAccount.generateOTKsIfNeeded(this._storage);
             await this._e2eeAccount.uploadKeys(this._storage);
             await this._deviceMessageHandler.decryptPending(this.rooms);
+
+            const txn = await this._storage.readTxn([
+                this._storage.storeNames.session,
+                this._storage.storeNames.accountData,
+            ]);
+            // try set up session backup if we stored the ssss key
+            const ssssKey = await ssssReadKey(txn);
+            if (ssssKey) {
+                // txn will end here as this does a network request
+                await this._createSessionBackup(ssssKey, txn);
+            }
         }
     }
 
@@ -200,6 +263,7 @@ export class Session {
     stop() {
         this._olmWorker?.dispose();
         this._sendScheduler.stop();
+        this._sessionBackup?.dispose();
     }
 
     async start(lastVersionResponse) {

src/matrix/e2ee/RoomEncryption.js

@@ -22,7 +22,7 @@ import {makeTxnId} from "../common.js";
 const ENCRYPTED_TYPE = "m.room.encrypted";
 
 export class RoomEncryption {
-    constructor({room, deviceTracker, olmEncryption, megolmEncryption, megolmDecryption, encryptionParams, storage}) {
+    constructor({room, deviceTracker, olmEncryption, megolmEncryption, megolmDecryption, encryptionParams, storage, sessionBackup}) {
         this._room = room;
         this._deviceTracker = deviceTracker;
         this._olmEncryption = olmEncryption;
@@ -37,10 +37,13 @@ export class RoomEncryption {
         this._eventIdsByMissingSession = new Map();
         this._senderDeviceCache = new Map();
         this._storage = storage;
-        this._sessionBackup = null;
+        this._sessionBackup = sessionBackup;
     }
 
-    setSessionBackup(sessionBackup) {
+    enableSessionBackup(sessionBackup) {
+        if (this._sessionBackup) {
+            return;
+        }
         this._sessionBackup = sessionBackup;
         // TODO: query session backup for all missing sessions so far
         // can we query multiple? no, only for sessionId, all for room, or all

src/matrix/e2ee/megolm/Decryption.js

@@ -159,6 +159,7 @@ export class Decryption {
     async addRoomKeyFromBackup(roomId, sessionId, sessionInfo, txn) {
         const sessionKey = sessionInfo["session_key"];
         const senderKey = sessionInfo["sender_key"];
+        // TODO: can we just trust this?
         const claimedEd25519Key = sessionInfo["sender_claimed_keys"]?.["ed25519"];
 
         if (

src/matrix/e2ee/megolm/SessionBackup.js

@@ -17,31 +17,28 @@ limitations under the License.
 import {base64} from "../../utils/base-encoding.js";
 
 export class SessionBackup {
-    constructor({olm, backupInfo, privateKey, hsApi}) {
-        this._olm = olm;
+    constructor({backupInfo, decryption, hsApi}) {
         this._backupInfo = backupInfo;
-        this._privateKey = privateKey;
+        this._decryption = decryption;
         this._hsApi = hsApi;
     }
 
     async getSession(roomId, sessionId) {
         const sessionResponse = await this._hsApi.roomKeyForRoomAndSession(this._backupInfo.version, roomId, sessionId).response();
-        const decryption = new this._olm.PkDecryption();
-        try {
-            decryption.init_with_private_key(this._privateKey);
-            const sessionInfo = this._decryption.decrypt(
-                sessionResponse.session_data.ephemeral,
-                sessionResponse.session_data.mac,
-                sessionResponse.session_data.ciphertext,
-            );
-            return JSON.parse(sessionInfo);
-        } finally {
-            decryption.free();
-        }
+        const sessionInfo = this._decryption.decrypt(
+            sessionResponse.session_data.ephemeral,
+            sessionResponse.session_data.mac,
+            sessionResponse.session_data.ciphertext,
+        );
+        return JSON.parse(sessionInfo);
     }
 
-    static async fromSecretStorage({olm, secretStorage, hsApi}) {
-        const base64PrivateKey = await secretStorage.readSecret("m.megolm_backup.v1");
+    dispose() {
+        this._decryption.free();
+    }
+
+    static async fromSecretStorage({olm, secretStorage, hsApi, txn}) {
+        const base64PrivateKey = await secretStorage.readSecret("m.megolm_backup.v1", txn);
         if (base64PrivateKey) {
             const privateKey = base64.decode(base64PrivateKey);
             const backupInfo = await hsApi.roomKeysVersion().response();
@@ -52,10 +49,11 @@ export class SessionBackup {
                 if (pubKey !== expectedPubKey) {
                     throw new Error(`Bad backup key, public key does not match. Calculated ${pubKey} but expected ${expectedPubKey}`);
                 }
-            } finally {
+            } catch(err) {
                 decryption.free();
+                throw err;
             }
-            return new SessionBackup({olm, backupInfo, privateKey, hsApi});
+            return new SessionBackup({backupInfo, decryption, hsApi});
         }
     }
 }

src/matrix/room/Room.js

@@ -429,6 +429,10 @@ export class Room extends EventEmitter {
         return !!this._summary.encryption;
     }
 
+    enableSessionBackup(sessionBackup) {
+        this._roomEncryption?.enableSessionBackup(sessionBackup);
+    }
+
     get isTrackingMembers() {
         return this._summary.isTrackingMembers;
     }

src/matrix/ssss/SecretStorage.js

@@ -17,16 +17,12 @@ limitations under the License.
 import {base64} from "../../utils/base-encoding.js";
 
 export class SecretStorage {
-    constructor({key, storage, cryptoDriver}) {
+    constructor({key, cryptoDriver}) {
         this._key = key;
-        this._storage = storage;
         this._cryptoDriver = cryptoDriver;
     }
 
-    async readSecret(name) {
-        const txn = await this._storage.readTxn([
-            this._storage.storeNames.accountData
-        ]);
+    async readSecret(name, txn) {
         const accountData = await txn.accountData.get(name);
         if (!accountData) {
             return;

src/matrix/ssss/index.js

@@ -34,17 +34,8 @@ async function readDefaultKeyDescription(storage) {
     return new KeyDescription(id, keyAccountData);
 }
 
-export async function writeKey(storage, key) {
-    const txn = await storage.readWriteTxn([
-        storage.storeNames.session
-    ]);
-    try {
-        txn.session.set("ssssKey", {id: key.id, binaryKey: key.binaryKey});
-    } catch (err) {
-        txn.abort();
-        throw err;
-    }
-    await txn.complete();
+export async function writeKey(key, txn) {
+    txn.session.set("ssssKey", {id: key.id, binaryKey: key.binaryKey});
 }
 
 export async function readKey(txn) {