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first draft of megolm decryption
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@ -14,12 +14,97 @@ See the License for the specific language governing permissions and
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limitations under the License.
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limitations under the License.
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*/
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*/
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import {DecryptionError} from "../common.js";
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const CACHE_MAX_SIZE = 10;
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export class Decryption {
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export class Decryption {
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constructor({pickleKey, olm}) {
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constructor({pickleKey, olm}) {
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this._pickleKey = pickleKey;
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this._pickleKey = pickleKey;
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this._olm = olm;
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this._olm = olm;
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}
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}
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createSessionCache() {
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return new SessionCache();
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}
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async decryptNewEvent(roomId, event, sessionCache, txn) {
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const {payload, messageIndex} = this._decrypt(roomId, event, sessionCache, txn);
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const sessionId = event.content?.["session_id"];
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this._handleReplayAttacks(roomId, sessionId, messageIndex, event, txn);
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return payload;
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}
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async decryptStoredEvent(roomId, event, sessionCache, txn) {
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const {payload} = this._decrypt(roomId, event, sessionCache, txn);
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return payload;
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}
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async _decrypt(roomId, event, sessionCache, txn) {
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const senderKey = event.content?.["sender_key"];
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const sessionId = event.content?.["session_id"];
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const ciphertext = event.content?.ciphertext;
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if (
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typeof senderKey !== "string" ||
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typeof sessionId !== "string" ||
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typeof ciphertext !== "string"
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) {
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throw new DecryptionError("MEGOLM_INVALID_EVENT", event);
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}
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let session = sessionCache.get(roomId, senderKey, sessionId);
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if (!session) {
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const sessionEntry = await txn.inboundGroupSessions.get(roomId, senderKey, sessionId);
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if (sessionEntry) {
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session = new this._olm.InboundGroupSession();
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try {
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session.unpickle(this._pickleKey, sessionEntry.session);
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} catch (err) {
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session.free();
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throw err;
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}
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sessionCache.add(roomId, senderKey, session);
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}
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}
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if (!session) {
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return;
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}
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const {plaintext, message_index: messageIndex} = session.decrypt(ciphertext);
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let payload;
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try {
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payload = JSON.parse(plaintext);
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} catch (err) {
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throw new DecryptionError("NOT_JSON", event, {plaintext, err});
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}
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if (payload.room_id !== roomId) {
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throw new DecryptionError("MEGOLM_WRONG_ROOM", event,
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{encryptedRoomId: payload.room_id, eventRoomId: roomId});
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}
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return {payload, messageIndex};
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}
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async _handleReplayAttacks(roomId, sessionId, messageIndex, event, txn) {
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const eventId = event.event_id;
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const timestamp = event.origin_server_ts;
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const decryption = await txn.groupSessionDecryptions.get(roomId, sessionId, messageIndex);
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if (decryption && decryption.eventId !== eventId) {
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// the one with the newest timestamp should be the attack
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const decryptedEventIsBad = decryption.timestamp < timestamp;
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const badEventId = decryptedEventIsBad ? eventId : decryption.eventId;
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throw new DecryptionError("MEGOLM_REPLAY_ATTACK", event, {badEventId, otherEventId: decryption.eventId});
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}
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if (!decryption) {
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txn.groupSessionDecryptions.set({
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roomId,
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sessionId,
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messageIndex,
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eventId,
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timestamp
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});
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}
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}
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async addRoomKeys(payloads, txn) {
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async addRoomKeys(payloads, txn) {
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const newSessions = [];
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const newSessions = [];
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for (const {senderKey, event} of payloads) {
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for (const {senderKey, event} of payloads) {
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@ -56,13 +141,49 @@ export class Decryption {
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}
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}
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}
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}
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// this will be passed to the Room in notifyRoomKeys
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return newSessions;
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return newSessions;
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}
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}
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}
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applyRoomKeyChanges(newSessions) {
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class SessionCache {
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// retry decryption with the new sessions
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constructor() {
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if (newSessions.length) {
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this._sessions = [];
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console.log(`I have ${newSessions.length} new inbound group sessions`, newSessions)
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}
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get(roomId, senderKey, sessionId) {
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const idx = this._sessions.findIndex(s => {
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return s.roomId === roomId &&
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s.senderKey === senderKey &&
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sessionId === s.session.session_id();
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});
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if (idx !== -1) {
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const entry = this._sessions[idx];
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// move to top
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if (idx > 0) {
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this._sessions.splice(idx, 1);
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this._sessions.unshift(entry);
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}
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return entry.session;
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}
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}
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}
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}
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add(roomId, senderKey, session) {
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// add new at top
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this._sessions.unshift({roomId, senderKey, session});
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if (this._sessions.length > CACHE_MAX_SIZE) {
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// free sessions we're about to remove
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for (let i = CACHE_MAX_SIZE; i < this._sessions.length; i += 1) {
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this._sessions[i].session.free();
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}
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this._sessions = this._sessions.slice(0, CACHE_MAX_SIZE);
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}
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}
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dispose() {
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for (const entry of this._sessions) {
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entry.session.free();
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}
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}
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}
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}
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