Element-R: pass pickleKey in as raw key for indexeddb encryption (#12543

)

* Element-R: pass pickleKey in as raw key for indexeddb encryption

Currently, we pass the `pickleKey` to the rust library for use as a passphrase
for encrypting its crypto store. The Rust libary then passes that passphrase
through 200000 rounds of PBKDF2 to generate an encryption key, which is
(deliberately) slow.

However, the pickleKey is actually 32 bytes of random data (base64-encoded). By
passing the raw key into the rust library, we can therefore save the PBKDF
operation.

Backwards-compatibility with existing sessions is maintained, because if the
rust library discovers that the store was previously encrypted with a key based
on a PBKDF, it will re-base64 and PBKDF the key we provide, thus reconstructing
the right key.

* Update src/Lifecycle.ts

Co-authored-by: Florian Duros <florianduros@element.io>

* Lifecycle-test: clean up test setup

Rely less on the unit under test for setting up the test preconditions -- not
least because we don't really want to fire up matrix clients and the like
during test setup.

* Factor out "encryptPickleKey" method

For a start it makes it easier to grok what's going on, but also I went to use
this in a test

* Improve tests for `Lifecycle.restoreFromLocalStorage`

---------

Co-authored-by: Florian Duros <florianduros@element.io>

src/BasePlatform.ts

@@ -38,7 +38,7 @@ import { idbLoad, idbSave, idbDelete } from "./utils/StorageAccess";
 import { ViewRoomPayload } from "./dispatcher/payloads/ViewRoomPayload";
 import { IConfigOptions } from "./IConfigOptions";
 import SdkConfig from "./SdkConfig";
-import { buildAndEncodePickleKey, getPickleAdditionalData } from "./utils/tokens/pickling";
+import { buildAndEncodePickleKey, encryptPickleKey } from "./utils/tokens/pickling";
 
 export const SSO_HOMESERVER_URL_KEY = "mx_sso_hs_url";
 export const SSO_ID_SERVER_URL_KEY = "mx_sso_is_url";
@@ -378,24 +378,16 @@ export default abstract class BasePlatform {
      *     support storing pickle keys.
      */
     public async createPickleKey(userId: string, deviceId: string): Promise<string | null> {
-        if (!window.crypto || !window.crypto.subtle) {
-            return null;
-        }
-        const crypto = window.crypto;
         const randomArray = new Uint8Array(32);
         crypto.getRandomValues(randomArray);
-        const cryptoKey = await crypto.subtle.generateKey({ name: "AES-GCM", length: 256 }, false, [
-            "encrypt",
-            "decrypt",
-        ]);
-        const iv = new Uint8Array(32);
-        crypto.getRandomValues(iv);
-
-        const additionalData = getPickleAdditionalData(userId, deviceId);
-        const encrypted = await crypto.subtle.encrypt({ name: "AES-GCM", iv, additionalData }, cryptoKey, randomArray);
+        const data = await encryptPickleKey(randomArray, userId, deviceId);
+        if (data === undefined) {
+            // no crypto support
+            return null;
+        }
 
         try {
-            await idbSave("pickleKey", [userId, deviceId], { encrypted, iv, cryptoKey });
+            await idbSave("pickleKey", [userId, deviceId], data);
         } catch (e) {
             return null;
         }

src/Lifecycle.ts

@@ -18,12 +18,12 @@ limitations under the License.
 */
 
 import { ReactNode } from "react";
-import { createClient, MatrixClient, SSOAction, OidcTokenRefresher } from "matrix-js-sdk/src/matrix";
+import { createClient, MatrixClient, SSOAction, OidcTokenRefresher, decodeBase64 } from "matrix-js-sdk/src/matrix";
 import { IEncryptedPayload } from "matrix-js-sdk/src/crypto/aes";
 import { QueryDict } from "matrix-js-sdk/src/utils";
 import { logger } from "matrix-js-sdk/src/logger";
 
-import { IMatrixClientCreds, MatrixClientPeg } from "./MatrixClientPeg";
+import { IMatrixClientCreds, MatrixClientPeg, MatrixClientPegAssignOpts } from "./MatrixClientPeg";
 import { ModuleRunner } from "./modules/ModuleRunner";
 import EventIndexPeg from "./indexing/EventIndexPeg";
 import createMatrixClient from "./utils/createMatrixClient";
@@ -422,6 +422,7 @@ async function onSuccessfulDelegatedAuthLogin(credentials: IMatrixClientCreds):
 }
 
 type TryAgainFunction = () => void;
+
 /**
  * Display a friendly error to the user when token login or OIDC authorization fails
  * @param description error description
@@ -821,7 +822,23 @@ async function doSetLoggedIn(credentials: IMatrixClientCreds, clearStorageEnable
     checkSessionLock();
 
     dis.fire(Action.OnLoggedIn);
-    await startMatrixClient(client, /*startSyncing=*/ !softLogout);
+
+    const clientPegOpts: MatrixClientPegAssignOpts = {};
+    if (credentials.pickleKey) {
+        // The pickleKey, if provided, is probably a base64-encoded 256-bit key, so can be used for the crypto store.
+        if (credentials.pickleKey.length === 43) {
+            clientPegOpts.rustCryptoStoreKey = decodeBase64(credentials.pickleKey);
+        } else {
+            // We have some legacy pickle key. Continue using it as a password.
+            clientPegOpts.rustCryptoStorePassword = credentials.pickleKey;
+        }
+    }
+
+    try {
+        await startMatrixClient(client, /*startSyncing=*/ !softLogout, clientPegOpts);
+    } finally {
+        clientPegOpts.rustCryptoStoreKey?.fill(0);
+    }
 
     return client;
 }
@@ -955,11 +972,16 @@ export function isLoggingOut(): boolean {
 /**
  * Starts the matrix client and all other react-sdk services that
  * listen for events while a session is logged in.
+ *
  * @param client the matrix client to start
- * @param {boolean} startSyncing True (default) to actually start
- * syncing the client.
+ * @param startSyncing - `true` to actually start syncing the client.
+ * @param clientPegOpts - Options to pass through to {@link MatrixClientPeg.start}.
  */
-async function startMatrixClient(client: MatrixClient, startSyncing = true): Promise<void> {
+async function startMatrixClient(
+    client: MatrixClient,
+    startSyncing: boolean,
+    clientPegOpts: MatrixClientPegAssignOpts,
+): Promise<void> {
     logger.log(`Lifecycle: Starting MatrixClient`);
 
     // dispatch this before starting the matrix client: it's used
@@ -990,10 +1012,10 @@ async function startMatrixClient(client: MatrixClient, startSyncing = true): Pro
         // index (e.g. the FilePanel), therefore initialize the event index
         // before the client.
         await EventIndexPeg.init();
-        await MatrixClientPeg.start();
+        await MatrixClientPeg.start(clientPegOpts);
     } else {
         logger.warn("Caller requested only auxiliary services be started");
-        await MatrixClientPeg.assign();
+        await MatrixClientPeg.assign(clientPegOpts);
     }
 
     checkSessionLock();

src/MatrixClientPeg.ts

@@ -66,6 +66,27 @@ export interface IMatrixClientCreds {
     freshLogin?: boolean;
 }
 
+export interface MatrixClientPegAssignOpts {
+    /**
+     * If we are using Rust crypto, a key with which to encrypt the indexeddb.
+     *
+     * If provided, it must be exactly 32 bytes of data. If both this and
+     * {@link MatrixClientPegAssignOpts.rustCryptoStorePassword} are undefined,
+     * the store will be unencrypted.
+     */
+    rustCryptoStoreKey?: Uint8Array;
+
+    /**
+     * If we are using Rust crypto, a password which will be used to derive a key to encrypt the store with.
+     *
+     * An alternative to {@link MatrixClientPegAssignOpts.rustCryptoStoreKey}. Ignored if `rustCryptoStoreKey` is set.
+     *
+     * Deriving a key from a password is (deliberately) a slow operation, so prefer to pass a `rustCryptoStoreKey`
+     * directly where possible.
+     */
+    rustCryptoStorePassword?: string;
+}
+
 /**
  * Holds the current instance of the `MatrixClient` to use across the codebase.
  * Looking for an `MatrixClient`? Just look for the `MatrixClientPeg` on the peg
@@ -94,14 +115,14 @@ export interface IMatrixClientPeg {
     unset(): void;
 
     /**
-     * Prepare the MatrixClient for use, including initialising the store and crypto, but do not start it
+     * Prepare the MatrixClient for use, including initialising the store and crypto, but do not start it.
      */
-    assign(): Promise<IStartClientOpts>;
+    assign(opts?: MatrixClientPegAssignOpts): Promise<IStartClientOpts>;
 
     /**
-     * Prepare the MatrixClient for use, including initialising the store and crypto, and start it
+     * Prepare the MatrixClient for use, including initialising the store and crypto, and start it.
      */
-    start(): Promise<void>;
+    start(opts?: MatrixClientPegAssignOpts): Promise<void>;
 
     /**
      * If we've registered a user ID we set this to the ID of the
@@ -248,7 +269,10 @@ class MatrixClientPegClass implements IMatrixClientPeg {
         PlatformPeg.get()?.reload();
     };
 
-    public async assign(): Promise<IStartClientOpts> {
+    /**
+     * Implementation of {@link IMatrixClientPeg.assign}.
+     */
+    public async assign(assignOpts: MatrixClientPegAssignOpts = {}): Promise<IStartClientOpts> {
         if (!this.matrixClient) {
             throw new Error("createClient must be called first");
         }
@@ -275,7 +299,7 @@ class MatrixClientPegClass implements IMatrixClientPeg {
 
         // try to initialise e2e on the new client
         if (!SettingsStore.getValue("lowBandwidth")) {
-            await this.initClientCrypto();
+            await this.initClientCrypto(assignOpts.rustCryptoStoreKey, assignOpts.rustCryptoStorePassword);
         }
 
         const opts = utils.deepCopy(this.opts);
@@ -301,8 +325,16 @@ class MatrixClientPegClass implements IMatrixClientPeg {
 
     /**
      * Attempt to initialize the crypto layer on a newly-created MatrixClient
+     *
+     * @param rustCryptoStoreKey - If we are using Rust crypto, a key with which to encrypt the indexeddb.
+     *   If provided, it must be exactly 32 bytes of data. If both this and `rustCryptoStorePassword` are
+     *   undefined, the store will be unencrypted.
+     *
+     * @param rustCryptoStorePassword - An alternative to `rustCryptoStoreKey`. Ignored if `rustCryptoStoreKey` is set.
+     *    A password which will be used to derive a key to encrypt the store with. Deriving a key from a password is
+     *    (deliberately) a slow operation, so prefer to pass a `rustCryptoStoreKey` directly where possible.
      */
-    private async initClientCrypto(): Promise<void> {
+    private async initClientCrypto(rustCryptoStoreKey?: Uint8Array, rustCryptoStorePassword?: string): Promise<void> {
         if (!this.matrixClient) {
             throw new Error("createClient must be called first");
         }
@@ -338,7 +370,13 @@ class MatrixClientPegClass implements IMatrixClientPeg {
 
         // Now we can initialise the right crypto impl.
         if (useRustCrypto) {
-            await this.matrixClient.initRustCrypto();
+            if (!rustCryptoStoreKey && !rustCryptoStorePassword) {
+                logger.error("Warning! Not using an encryption key for rust crypto store.");
+            }
+            await this.matrixClient.initRustCrypto({
+                storageKey: rustCryptoStoreKey,
+                storagePassword: rustCryptoStorePassword,
+            });
 
             StorageManager.setCryptoInitialised(true);
             // TODO: device dehydration and whathaveyou
@@ -367,8 +405,11 @@ class MatrixClientPegClass implements IMatrixClientPeg {
         }
     }
 
-    public async start(): Promise<void> {
-        const opts = await this.assign();
+    /**
+     * Implementation of {@link IMatrixClientPeg.start}.
+     */
+    public async start(assignOpts?: MatrixClientPegAssignOpts): Promise<void> {
+        const opts = await this.assign(assignOpts);
 
         logger.log(`MatrixClientPeg: really starting MatrixClient`);
         await this.matrixClient!.startClient(opts);

src/utils/tokens/pickling.ts

@@ -20,6 +20,20 @@ limitations under the License.
 import { encodeUnpaddedBase64 } from "matrix-js-sdk/src/matrix";
 import { logger } from "matrix-js-sdk/src/logger";
 
+/**
+ * Encrypted format of a pickle key, as stored in IndexedDB.
+ */
+export interface EncryptedPickleKey {
+    /** The encrypted payload. */
+    encrypted?: BufferSource;
+
+    /** Initialisation vector for the encryption. */
+    iv?: BufferSource;
+
+    /** The encryption key which was used to encrypt the payload. */
+    cryptoKey?: CryptoKey;
+}
+
 /**
  * Calculates the `additionalData` for the AES-GCM key used by the pickling processes. This
  * additional data is *not* encrypted, but *is* authenticated. The additional data is constructed
@@ -46,6 +60,32 @@ export function getPickleAdditionalData(userId: string, deviceId: string): Uint8
     return additionalData;
 }
 
+/**
+ * Encrypt the given pickle key, ready for storage in the database.
+ *
+ * @param pickleKey - The key to be encrypted.
+ * @param userId - The user ID the pickle key belongs to.
+ * @param deviceId - The device ID the pickle key belongs to.
+ *
+ * @returns Data object ready for storing in indexeddb.
+ */
+export async function encryptPickleKey(
+    pickleKey: Uint8Array,
+    userId: string,
+    deviceId: string,
+): Promise<EncryptedPickleKey | undefined> {
+    if (!crypto?.subtle) {
+        return undefined;
+    }
+    const cryptoKey = await crypto.subtle.generateKey({ name: "AES-GCM", length: 256 }, false, ["encrypt", "decrypt"]);
+    const iv = new Uint8Array(32);
+    crypto.getRandomValues(iv);
+
+    const additionalData = getPickleAdditionalData(userId, deviceId);
+    const encrypted = await crypto.subtle.encrypt({ name: "AES-GCM", iv, additionalData }, cryptoKey, pickleKey);
+    return { encrypted, iv, cryptoKey };
+}
+
 /**
  * Decrypts the provided data into a pickle key and base64-encodes it ready for use elsewhere.
  *
@@ -59,7 +99,7 @@ export function getPickleAdditionalData(userId: string, deviceId: string): Uint8
  * @returns A promise that resolves to the encoded pickle key, or undefined if the key cannot be built and encoded.
  */
 export async function buildAndEncodePickleKey(
-    data: { encrypted?: BufferSource; iv?: BufferSource; cryptoKey?: CryptoKey } | undefined,
+    data: EncryptedPickleKey | undefined,
     userId: string,
     deviceId: string,
 ): Promise<string | undefined> {