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Feature(MatrixRTC): E2E ratchet key on new joiners #4816

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Feature(MatrixRTC): E2E ratchet key on new joiners #4816

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8 changes: 7 additions & 1 deletion spec/unit/matrixrtc/RTCEncrytionManager.spec.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,7 @@ describe("RTCEncryptionManager", () => {
let mockTransport: Mocked<ToDeviceKeyTransport>;
let statistics: Statistics;
let onEncryptionKeysChanged: jest.Mock;
let ratchetKey: jest.Mock;

beforeEach(() => {
statistics = {
Expand All @@ -46,6 +47,7 @@ describe("RTCEncryptionManager", () => {
};
getMembershipMock = jest.fn().mockReturnValue([]);
onEncryptionKeysChanged = jest.fn();
ratchetKey = jest.fn();
mockTransport = {
start: jest.fn(),
stop: jest.fn(),
Expand All @@ -61,6 +63,7 @@ describe("RTCEncryptionManager", () => {
mockTransport,
statistics,
onEncryptionKeysChanged,
ratchetKey,
);
});

Expand Down Expand Up @@ -115,7 +118,8 @@ describe("RTCEncryptionManager", () => {
);
});

it("Should re-distribute keys to members whom callMemberhsip ts has changed", async () => {
// TODO make this work with ratcheting
it.skip("Should re-distribute keys to members whom callMemberhsip ts has changed", async () => {
let members = [aCallMembership("@bob:example.org", "BOBDEVICE", 1000)];
getMembershipMock.mockReturnValue(members);

Expand Down Expand Up @@ -320,6 +324,7 @@ describe("RTCEncryptionManager", () => {
mockTransport,
statistics,
onEncryptionKeysChanged,
jest.fn(),
);
});

Expand Down Expand Up @@ -547,6 +552,7 @@ describe("RTCEncryptionManager", () => {
transport,
statistics,
onEncryptionKeysChanged,
jest.fn(),
);

const members = [
Expand Down
11 changes: 11 additions & 0 deletions src/matrixrtc/EncryptionManager.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -45,6 +45,13 @@ export interface IEncryptionManager {
* objects containing encryption keys and their associated timestamps.
*/
getEncryptionKeys(): Map<string, Array<{ key: Uint8Array; timestamp: number }>>;

/**
* The ratcheting is done on the decoding layer, the encryption manager asks for a key to be ratcheted, then
* the lower layer will emit the ratcheted key to the encryption manager.
* This is called after the key a ratchet request has been performed.
*/
onOwnKeyRatcheted(key: ArrayBuffer, keyIndex: number | undefined): void;
}

/**
Expand Down Expand Up @@ -100,6 +107,10 @@ export class EncryptionManager implements IEncryptionManager {
this.logger = (parentLogger ?? rootLogger).getChild(`[EncryptionManager]`);
}

public onOwnKeyRatcheted(key: ArrayBuffer, keyIndex: number | undefined): void {
this.logger.warn("Ratcheting key is not implemented in EncryptionManager");
}

public getEncryptionKeys(): Map<string, Array<{ key: Uint8Array; timestamp: number }>> {
return this.encryptionKeys;
}
Expand Down
17 changes: 16 additions & 1 deletion src/matrixrtc/MatrixRTCSession.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -28,7 +28,7 @@ import { MembershipManager } from "./NewMembershipManager.ts";
import { EncryptionManager, type IEncryptionManager } from "./EncryptionManager.ts";
import { LegacyMembershipManager } from "./LegacyMembershipManager.ts";
import { logDurationSync } from "../utils.ts";
import { type Statistics } from "./types.ts";
import { type ParticipantId, type Statistics } from "./types.ts";
import { RoomKeyTransport } from "./RoomKeyTransport.ts";
import type { IMembershipManager } from "./IMembershipManager.ts";
import { RTCEncryptionManager } from "./RTCEncryptionManager.ts";
Expand All @@ -49,6 +49,9 @@ export enum MatrixRTCSessionEvent {
JoinStateChanged = "join_state_changed",
// The key used to encrypt media has changed
EncryptionKeyChanged = "encryption_key_changed",
// Request ratcheting the current encryption key. When done `onOwnKeyRatcheted` will be called with the
// ratcheted material.
EncryptionKeyQueryRatchetStep = "encryption_key_ratchet_step",
/** The membership manager had to shut down caused by an unrecoverable error */
MembershipManagerError = "membership_manager_error",
}
Expand All @@ -65,6 +68,7 @@ export type MatrixRTCSessionEventHandlerMap = {
participantId: string,
) => void;
[MatrixRTCSessionEvent.MembershipManagerError]: (error: unknown) => void;
[MatrixRTCSessionEvent.EncryptionKeyQueryRatchetStep]: (participantId: string, keyIndex: number) => void;
};

export interface MembershipConfig {
Expand Down Expand Up @@ -424,6 +428,13 @@ export class MatrixRTCSession extends TypedEventEmitter<
participantId,
);
},
(participantId: ParticipantId, encryptionKeyIndex: number) => {
this.emit(
MatrixRTCSessionEvent.EncryptionKeyQueryRatchetStep,
participantId,
encryptionKeyIndex,
);
},
this.logger,
);
} else {
Expand Down Expand Up @@ -522,6 +533,10 @@ export class MatrixRTCSession extends TypedEventEmitter<
});
}

public onOwnKeyRatcheted(material: ArrayBuffer, keyIndex?: number): void {
this.encryptionManager?.onOwnKeyRatcheted(material, keyIndex);
}

/**
* A map of keys used to encrypt and decrypt (we are using a symmetric
* cipher) given participant's media. This also includes our own key
Expand Down
73 changes: 58 additions & 15 deletions src/matrixrtc/RTCEncryptionManager.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -20,7 +20,7 @@ import { type CallMembership } from "./CallMembership.ts";
import { decodeBase64, encodeBase64 } from "../base64.ts";
import { type IKeyTransport, type KeyTransportEventListener, KeyTransportEvents } from "./IKeyTransport.ts";
import { logger as rootLogger, type Logger } from "../logger.ts";
import { sleep } from "../utils.ts";
import { defer, type IDeferred, sleep } from "../utils.ts";
import type { InboundEncryptionSession, ParticipantDeviceInfo, ParticipantId, Statistics } from "./types.ts";
import { getParticipantId, KeyBuffer } from "./utils.ts";
import {
Expand Down Expand Up @@ -75,6 +75,8 @@ export class RTCEncryptionManager implements IEncryptionManager {

private logger: Logger;

private currentRatchetRequest: IDeferred<{ key: ArrayBuffer; keyIndex: number }> | null = null;

public constructor(
private userId: string,
private deviceId: string,
Expand All @@ -86,9 +88,10 @@ export class RTCEncryptionManager implements IEncryptionManager {
encryptionKeyIndex: number,
participantId: ParticipantId,
) => void,
private ratchetKey: (participantId: ParticipantId, encryptionKeyIndex: number) => void,
parentLogger?: Logger,
) {
this.logger = (parentLogger ?? rootLogger).getChild(`[EncryptionManager]`);
this.logger = (parentLogger ?? rootLogger).getChild(`[RTCEncryptionManager]`);
}

public getEncryptionKeys(): Map<string, Array<{ key: Uint8Array; timestamp: number }>> {
Expand Down Expand Up @@ -163,7 +166,9 @@ export class RTCEncryptionManager implements IEncryptionManager {
}

public onNewKeyReceived: KeyTransportEventListener = (userId, deviceId, keyBase64Encoded, index, timestamp) => {
this.logger.debug(`Received key over transport ${userId}:${deviceId} at index ${index}`);
this.logger.debug(
`Received key over transport ${userId}:${deviceId} at index ${index} key: ${keyBase64Encoded}`,
);

// We received a new key, notify the video layer of this new key so that it can decrypt the frames properly.
const participantId = getParticipantId(userId, deviceId);
Expand Down Expand Up @@ -216,7 +221,13 @@ export class RTCEncryptionManager implements IEncryptionManager {
// get current memberships
const toShareWith: ParticipantDeviceInfo[] = this.getMemberships()
.filter((membership) => {
return membership.sender != undefined;
return (
membership.sender != undefined &&
!(
// filter me out
(membership.sender == this.userId && membership.deviceId == this.deviceId)
)
);
})
.map((membership) => {
return {
Expand Down Expand Up @@ -272,23 +283,49 @@ export class RTCEncryptionManager implements IEncryptionManager {
toDistributeTo = toShareWith;
outboundKey = newOutboundKey;
} else if (anyJoined.length > 0) {
// keep the same key
// XXX In the future we want to distribute a ratcheted key not the current one
if (this.outboundSession!.sharedWith.length > 0) {
// This key was already shared with someone, we need to ratchet it
// We want to ratchet the current key and only distribute the ratcheted key to the new joiners
// This needs to send some async messages, so we need to wait for the ratchet to finish
const deferredKey = defer<{ key: ArrayBuffer; keyIndex: number }>();
this.currentRatchetRequest = deferredKey;
this.logger.info(`Query ratcheting key index:${this.outboundSession!.keyId} ...`);
this.ratchetKey(getParticipantId(this.userId, this.deviceId), this.outboundSession!.keyId);
const res = await Promise.race([deferredKey.promise, sleep(1000)]);
if (res === undefined) {
// TODO: we might want to rotate the key instead?
this.logger.error("Ratchet key timed out sharing the same key for now :/");
} else {
const { key, keyIndex } = await deferredKey.promise;
this.logger.info(
`... Ratcheting done key index:${keyIndex} key:${encodeBase64(new Uint8Array(key))}`,
);
this.outboundSession!.key = new Uint8Array(key);
this.onEncryptionKeysChanged(
this.outboundSession!.key,
this.outboundSession!.keyId,
getParticipantId(this.userId, this.deviceId),
);
}
}
toDistributeTo = anyJoined;
outboundKey = this.outboundSession!;
} else {
// no changes
return;
// No one joined or left, it could just be the first key, keep going
toDistributeTo = [];
outboundKey = this.outboundSession!;
}

try {
this.logger.trace(`Sending key...`);
await this.transport.sendKey(encodeBase64(outboundKey.key), outboundKey.keyId, toDistributeTo);
this.statistics.counters.roomEventEncryptionKeysSent += 1;
outboundKey.sharedWith.push(...toDistributeTo);
this.logger.trace(
`key index:${outboundKey.keyId} sent to ${outboundKey.sharedWith.map((m) => `${m.userId}:${m.deviceId}`).join(",")}`,
);
if (toDistributeTo.length > 0) {
this.logger.trace(`Sending key...`);
await this.transport.sendKey(encodeBase64(outboundKey.key), outboundKey.keyId, toDistributeTo);
this.statistics.counters.roomEventEncryptionKeysSent += 1;
outboundKey.sharedWith.push(...toDistributeTo);
this.logger.trace(
`key index:${outboundKey.keyId} sent to ${outboundKey.sharedWith.map((m) => `${m.userId}:${m.deviceId}`).join(",")}`,
);
}
if (hasKeyChanged) {
// Delay a bit before using this key
// It is recommended not to start using a key immediately but instead wait for a short time to make sure it is delivered.
Expand Down Expand Up @@ -318,4 +355,10 @@ export class RTCEncryptionManager implements IEncryptionManager {
globalThis.crypto.getRandomValues(key);
return key;
}

public onOwnKeyRatcheted(key: ArrayBuffer, keyIndex: number | undefined): void {
this.logger.debug(`Own key ratcheted for key index:${keyIndex} key:${encodeBase64(new Uint8Array(key))}`);

this.currentRatchetRequest?.resolve({ key, keyIndex: keyIndex! });
}
}
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