From 2d6230f19994cac347424525637771821a998775 Mon Sep 17 00:00:00 2001
From: Hugh Nimmo-Smith <hughns@users.noreply.github.com>
Date: Fri, 27 Sep 2024 16:54:48 +0100
Subject: [PATCH] Rotate RTC key when a new member joins (#4422)

---
 spec/unit/matrixrtc/MatrixRTCSession.spec.ts | 21 +++++++++++++-------
 src/matrixrtc/MatrixRTCSession.ts            |  6 +++---
 2 files changed, 17 insertions(+), 10 deletions(-)

diff --git a/spec/unit/matrixrtc/MatrixRTCSession.spec.ts b/spec/unit/matrixrtc/MatrixRTCSession.spec.ts
index 31614010396..e3572b88d54 100644
--- a/spec/unit/matrixrtc/MatrixRTCSession.spec.ts
+++ b/spec/unit/matrixrtc/MatrixRTCSession.spec.ts
@@ -686,25 +686,27 @@ describe("MatrixRTCSession", () => {
             expect(client.cancelPendingEvent).toHaveBeenCalledWith(eventSentinel);
         });
 
-        it("Re-sends key if a new member joins", async () => {
+        it("Rotates key if a new member joins", async () => {
             jest.useFakeTimers();
             try {
                 const mockRoom = makeMockRoom([membershipTemplate]);
                 sess = MatrixRTCSession.roomSessionForRoom(client, mockRoom);
 
-                const keysSentPromise1 = new Promise((resolve) => {
-                    sendEventMock.mockImplementation(resolve);
+                const keysSentPromise1 = new Promise<EncryptionKeysEventContent>((resolve) => {
+                    sendEventMock.mockImplementation((_roomId, _evType, payload) => resolve(payload));
                 });
 
                 sess.joinRoomSession([mockFocus], mockFocus, { manageMediaKeys: true });
-                await keysSentPromise1;
+                const firstKeysPayload = await keysSentPromise1;
+                expect(firstKeysPayload.keys).toHaveLength(1);
+                expect(firstKeysPayload.keys[0].index).toEqual(0);
                 expect(sess!.statistics.counters.roomEventEncryptionKeysSent).toEqual(1);
 
                 sendEventMock.mockClear();
                 jest.advanceTimersByTime(10000);
 
-                const keysSentPromise2 = new Promise((resolve) => {
-                    sendEventMock.mockImplementation(resolve);
+                const keysSentPromise2 = new Promise<EncryptionKeysEventContent>((resolve) => {
+                    sendEventMock.mockImplementation((_roomId, _evType, payload) => resolve(payload));
                 });
 
                 const onMembershipsChanged = jest.fn();
@@ -719,9 +721,14 @@ describe("MatrixRTCSession", () => {
                     .mockReturnValue(makeMockRoomState([membershipTemplate, member2], mockRoom.roomId));
                 sess.onMembershipUpdate();
 
-                await keysSentPromise2;
+                jest.advanceTimersByTime(10000);
+
+                const secondKeysPayload = await keysSentPromise2;
 
                 expect(sendEventMock).toHaveBeenCalled();
+                expect(secondKeysPayload.keys).toHaveLength(1);
+                expect(secondKeysPayload.keys[0].index).toEqual(1);
+                expect(secondKeysPayload.keys[0].key).not.toEqual(firstKeysPayload.keys[0].key);
                 expect(sess!.statistics.counters.roomEventEncryptionKeysSent).toEqual(2);
             } finally {
                 jest.useRealTimers();
diff --git a/src/matrixrtc/MatrixRTCSession.ts b/src/matrixrtc/MatrixRTCSession.ts
index 1cf486062f7..5a1d6e6e73d 100644
--- a/src/matrixrtc/MatrixRTCSession.ts
+++ b/src/matrixrtc/MatrixRTCSession.ts
@@ -776,8 +776,8 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
                 logger.debug(`Member(s) have left: queueing sender key rotation`);
                 this.makeNewKeyTimeout = setTimeout(this.onRotateKeyTimeout, MAKE_KEY_DELAY);
             } else if (anyJoined) {
-                logger.debug(`New member(s) have joined: re-sending keys`);
-                this.requestKeyEventSend();
+                logger.debug(`New member(s) have joined: queueing sender key rotation`);
+                this.makeNewKeyTimeout = setTimeout(this.onRotateKeyTimeout, MAKE_KEY_DELAY);
             } else if (oldFingerprints) {
                 // does it look like any of the members have updated their memberships?
                 const newFingerprints = this.lastMembershipFingerprints!;
@@ -788,7 +788,7 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
                     Array.from(oldFingerprints).some((x) => !newFingerprints.has(x)) ||
                     Array.from(newFingerprints).some((x) => !oldFingerprints.has(x));
                 if (candidateUpdates) {
-                    logger.debug(`Member(s) have updated/reconnected: re-sending keys`);
+                    logger.debug(`Member(s) have updated/reconnected: re-sending keys to everyone`);
                     this.requestKeyEventSend();
                 }
             }