Implement sharing of megolm keys

src/crypto/OlmDevice.js

@@ -796,6 +796,62 @@ OlmDevice.prototype.decryptGroupMessage = function(
     );
 };
 
+/**
+ * Determine if we have the keys for a given megolm session
+ *
+ * @param {string} roomId    room in which the message was received
+ * @param {string} senderKey base64-encoded curve25519 key of the sender
+ * @param {sring} sessionId session identifier
+ *
+ * @returns {boolean} true if we have the keys to this session
+ */
+OlmDevice.prototype.hasInboundSessionKeys = function(roomId, senderKey, sessionId) {
+    const s = this._sessionStore.getEndToEndInboundGroupSession(
+        senderKey, sessionId,
+    );
+
+    if (s === null) {
+        return false;
+    }
+
+    const r = JSON.parse(s);
+    if (roomId !== r.room_id) {
+        console.warn(
+            `requested keys for inbound group session ${senderKey}|` +
+            `${sessionId}, with incorrect room_id (expected ${r.room_id}, ` +
+            `was ${roomId})`,
+        );
+        return false;
+    }
+
+    return true;
+};
+
+/**
+ * Extract the keys to a given megolm session, for sharing
+ *
+ * @param {string} roomId    room in which the message was received
+ * @param {string} senderKey base64-encoded curve25519 key of the sender
+ * @param {string} sessionId session identifier
+ *
+ * @returns {{chain_index: number, key: string}} details of the session key. The
+ *    key is a base64-encoded megolm key in export format.
+ */
+OlmDevice.prototype.getInboundGroupSessionKey = function(roomId, senderKey, sessionId) {
+    function getKey(session, keysClaimed) {
+        const messageIndex = session.first_known_index();
+
+        return {
+            "chain_index": messageIndex,
+            "key": session.export_session(messageIndex),
+        };
+    }
+
+    return this._getInboundGroupSession(
+        roomId, senderKey, sessionId, getKey,
+    );
+};
+
 /**
  * Export an inbound group session
  *

src/crypto/algorithms/base.js

@@ -89,12 +89,11 @@ export {EncryptionAlgorithm}; // https://github.com/jsdoc3/jsdoc/issues/1272
 /**
  * base type for decryption implementations
  *
- * @alias module:crypto/algorithms/base.DecryptionAlgorithm
- *
  * @param {object} params parameters
  * @param {string} params.userId  The UserID for the local user
  * @param {module:crypto} params.crypto crypto core
  * @param {module:crypto/OlmDevice} params.olmDevice olm.js wrapper
+ * @param {module:base-apis~MatrixBaseApis} baseApis base matrix api interface
  * @param {string=} params.roomId The ID of the room we will be receiving
  *     from. Null for to-device events.
  */
@@ -103,6 +102,7 @@ class DecryptionAlgorithm {
         this._userId = params.userId;
         this._crypto = params.crypto;
         this._olmDevice = params.olmDevice;
+        this._baseApis = params.baseApis;
         this._roomId = params.roomId;
     }
 

src/crypto/algorithms/megolm.js

@@ -663,6 +663,89 @@ MegolmDecryption.prototype.onRoomKeyEvent = function(event) {
 };
 
 
+MegolmDecryption.prototype.hasKeysForKeyRequest = function(keyRequest) {
+    const body = keyRequest.requestBody;
+
+    return this._olmDevice.hasInboundSessionKeys(
+        body.room_id,
+        body.sender_key,
+        body.session_id,
+        // TODO: ratchet index
+    );
+};
+
+
+MegolmDecryption.prototype.shareKeysWithDevice = function(keyRequest) {
+    const userId = keyRequest.userId;
+    const deviceId = keyRequest.deviceId;
+    const deviceInfo = this._crypto.getStoredDevice(userId, deviceId);
+    const body = keyRequest.requestBody;
+
+    olmlib.ensureOlmSessionsForDevices(
+        this._olmDevice, this._baseApis, {
+            [userId]: [deviceInfo],
+        },
+    ).then((devicemap) => {
+        const olmSessionResult = devicemap[userId][deviceId];
+        if (!olmSessionResult.sessionId) {
+            // no session with this device, probably because there
+            // were no one-time keys.
+            //
+            // ensureOlmSessionsForUsers has already done the logging,
+            // so just skip it.
+            return;
+        }
+
+        console.log(
+            "sharing keys for session " + body.sender_key + "|"
+            + body.session_id + " with device "
+            + userId + ":" + deviceId,
+        );
+
+        const key = this._olmDevice.getInboundGroupSessionKey(
+            body.room_id, body.sender_key, body.session_id,
+        );
+
+        const payload = {
+            type: "m.forwarded_room_key",
+            content: {
+                algorithm: olmlib.MEGOLM_ALGORITHM,
+                room_id: body.room_id,
+                sender_key: body.sender_key,
+                session_id: body.session_id,
+                session_key: key.key,
+                chain_index: key.chain_index,
+            },
+        };
+
+        const encryptedContent = {
+            algorithm: olmlib.OLM_ALGORITHM,
+            sender_key: this._olmDevice.deviceCurve25519Key,
+            ciphertext: {},
+        };
+
+        olmlib.encryptMessageForDevice(
+            encryptedContent.ciphertext,
+            this._userId,
+            this._deviceId,
+            this._olmDevice,
+            userId,
+            deviceInfo,
+            payload,
+        );
+
+        const contentMap = {
+            [userId]: {
+                [deviceId]: encryptedContent,
+            },
+        };
+
+        // TODO: retries
+        return this._baseApis.sendToDevice("m.room.encrypted", contentMap);
+    }).done();
+};
+
+
 /**
  * @inheritdoc
  *

src/crypto/index.js

@@ -1238,6 +1238,7 @@ Crypto.prototype._getRoomDecryptor = function(roomId, algorithm) {
         userId: this._userId,
         crypto: this,
         olmDevice: this._olmDevice,
+        baseApis: this._baseApis,
         roomId: roomId,
     });