Updated 18 files, added 1692 files and deleted includes/system/compare.inc (automated)

1 files changed, 803 insertions, 0 deletions

diff --git a/includes/external/matrix/node_modules/matrix-js-sdk/src/crypto/CrossSigning.ts b/includes/external/matrix/node_modules/matrix-js-sdk/src/crypto/CrossSigning.ts
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@@ -0,0 +1,803 @@
+/*
+Copyright 2019 - 2021 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+/**
+ * Cross signing methods
+ */
+
+import { PkSigning } from "@matrix-org/olm";
+
+import { decodeBase64, encodeBase64, IObject, pkSign, pkVerify } from "./olmlib";
+import { logger } from "../logger";
+import { IndexedDBCryptoStore } from "../crypto/store/indexeddb-crypto-store";
+import { decryptAES, encryptAES } from "./aes";
+import { DeviceInfo } from "./deviceinfo";
+import { SecretStorage } from "./SecretStorage";
+import { ICrossSigningKey, ISignedKey, MatrixClient } from "../client";
+import { OlmDevice } from "./OlmDevice";
+import { ICryptoCallbacks } from ".";
+import { ISignatures } from "../@types/signed";
+import { CryptoStore, SecretStorePrivateKeys } from "./store/base";
+import { SecretStorageKeyDescription } from "../secret-storage";
+
+const KEY_REQUEST_TIMEOUT_MS = 1000 * 60;
+
+function publicKeyFromKeyInfo(keyInfo: ICrossSigningKey): string {
+    // `keys` is an object with { [`ed25519:${pubKey}`]: pubKey }
+    // We assume only a single key, and we want the bare form without type
+    // prefix, so we select the values.
+    return Object.values(keyInfo.keys)[0];
+}
+
+export interface ICacheCallbacks {
+    getCrossSigningKeyCache?(type: string, expectedPublicKey?: string): Promise<Uint8Array | null>;
+    storeCrossSigningKeyCache?(type: string, key?: Uint8Array): Promise<void>;
+}
+
+export interface ICrossSigningInfo {
+    keys: Record<string, ICrossSigningKey>;
+    firstUse: boolean;
+    crossSigningVerifiedBefore: boolean;
+}
+
+export class CrossSigningInfo {
+    public keys: Record<string, ICrossSigningKey> = {};
+    public firstUse = true;
+    // This tracks whether we've ever verified this user with any identity.
+    // When you verify a user, any devices online at the time that receive
+    // the verifying signature via the homeserver will latch this to true
+    // and can use it in the future to detect cases where the user has
+    // become unverified later for any reason.
+    private crossSigningVerifiedBefore = false;
+
+    /**
+     * Information about a user's cross-signing keys
+     *
+     * @param userId - the user that the information is about
+     * @param callbacks - Callbacks used to interact with the app
+     *     Requires getCrossSigningKey and saveCrossSigningKeys
+     * @param cacheCallbacks - Callbacks used to interact with the cache
+     */
+    public constructor(
+        public readonly userId: string,
+        private callbacks: ICryptoCallbacks = {},
+        private cacheCallbacks: ICacheCallbacks = {},
+    ) {}
+
+    public static fromStorage(obj: ICrossSigningInfo, userId: string): CrossSigningInfo {
+        const res = new CrossSigningInfo(userId);
+        for (const prop in obj) {
+            if (obj.hasOwnProperty(prop)) {
+                // @ts-ignore - ts doesn't like this and nor should we
+                res[prop] = obj[prop];
+            }
+        }
+        return res;
+    }
+
+    public toStorage(): ICrossSigningInfo {
+        return {
+            keys: this.keys,
+            firstUse: this.firstUse,
+            crossSigningVerifiedBefore: this.crossSigningVerifiedBefore,
+        };
+    }
+
+    /**
+     * Calls the app callback to ask for a private key
+     *
+     * @param type - The key type ("master", "self_signing", or "user_signing")
+     * @param expectedPubkey - The matching public key or undefined to use
+     *     the stored public key for the given key type.
+     * @returns An array with [ public key, Olm.PkSigning ]
+     */
+    public async getCrossSigningKey(type: string, expectedPubkey?: string): Promise<[string, PkSigning]> {
+        const shouldCache = ["master", "self_signing", "user_signing"].indexOf(type) >= 0;
+
+        if (!this.callbacks.getCrossSigningKey) {
+            throw new Error("No getCrossSigningKey callback supplied");
+        }
+
+        if (expectedPubkey === undefined) {
+            expectedPubkey = this.getId(type)!;
+        }
+
+        function validateKey(key: Uint8Array | null): [string, PkSigning] | undefined {
+            if (!key) return;
+            const signing = new global.Olm.PkSigning();
+            const gotPubkey = signing.init_with_seed(key);
+            if (gotPubkey === expectedPubkey) {
+                return [gotPubkey, signing];
+            }
+            signing.free();
+        }
+
+        let privkey: Uint8Array | null = null;
+        if (this.cacheCallbacks.getCrossSigningKeyCache && shouldCache) {
+            privkey = await this.cacheCallbacks.getCrossSigningKeyCache(type, expectedPubkey);
+        }
+
+        const cacheresult = validateKey(privkey);
+        if (cacheresult) {
+            return cacheresult;
+        }
+
+        privkey = await this.callbacks.getCrossSigningKey(type, expectedPubkey);
+        const result = validateKey(privkey);
+        if (result) {
+            if (this.cacheCallbacks.storeCrossSigningKeyCache && shouldCache) {
+                await this.cacheCallbacks.storeCrossSigningKeyCache(type, privkey!);
+            }
+            return result;
+        }
+
+        /* No keysource even returned a key */
+        if (!privkey) {
+            throw new Error("getCrossSigningKey callback for " + type + " returned falsey");
+        }
+
+        /* We got some keys from the keysource, but none of them were valid */
+        throw new Error("Key type " + type + " from getCrossSigningKey callback did not match");
+    }
+
+    /**
+     * Check whether the private keys exist in secret storage.
+     * XXX: This could be static, be we often seem to have an instance when we
+     * want to know this anyway...
+     *
+     * @param secretStorage - The secret store using account data
+     * @returns map of key name to key info the secret is encrypted
+     *     with, or null if it is not present or not encrypted with a trusted
+     *     key
+     */
+    public async isStoredInSecretStorage(
+        secretStorage: SecretStorage<MatrixClient | undefined>,
+    ): Promise<Record<string, object> | null> {
+        // check what SSSS keys have encrypted the master key (if any)
+        const stored = (await secretStorage.isStored("m.cross_signing.master")) || {};
+        // then check which of those SSSS keys have also encrypted the SSK and USK
+        function intersect(s: Record<string, SecretStorageKeyDescription>): void {
+            for (const k of Object.keys(stored)) {
+                if (!s[k]) {
+                    delete stored[k];
+                }
+            }
+        }
+        for (const type of ["self_signing", "user_signing"]) {
+            intersect((await secretStorage.isStored(`m.cross_signing.${type}`)) || {});
+        }
+        return Object.keys(stored).length ? stored : null;
+    }
+
+    /**
+     * Store private keys in secret storage for use by other devices. This is
+     * typically called in conjunction with the creation of new cross-signing
+     * keys.
+     *
+     * @param keys - The keys to store
+     * @param secretStorage - The secret store using account data
+     */
+    public static async storeInSecretStorage(
+        keys: Map<string, Uint8Array>,
+        secretStorage: SecretStorage<undefined>,
+    ): Promise<void> {
+        for (const [type, privateKey] of keys) {
+            const encodedKey = encodeBase64(privateKey);
+            await secretStorage.store(`m.cross_signing.${type}`, encodedKey);
+        }
+    }
+
+    /**
+     * Get private keys from secret storage created by some other device. This
+     * also passes the private keys to the app-specific callback.
+     *
+     * @param type - The type of key to get.  One of "master",
+     * "self_signing", or "user_signing".
+     * @param secretStorage - The secret store using account data
+     * @returns The private key
+     */
+    public static async getFromSecretStorage(type: string, secretStorage: SecretStorage): Promise<Uint8Array | null> {
+        const encodedKey = await secretStorage.get(`m.cross_signing.${type}`);
+        if (!encodedKey) {
+            return null;
+        }
+        return decodeBase64(encodedKey);
+    }
+
+    /**
+     * Check whether the private keys exist in the local key cache.
+     *
+     * @param type - The type of key to get. One of "master",
+     * "self_signing", or "user_signing". Optional, will check all by default.
+     * @returns True if all keys are stored in the local cache.
+     */
+    public async isStoredInKeyCache(type?: string): Promise<boolean> {
+        const cacheCallbacks = this.cacheCallbacks;
+        if (!cacheCallbacks) return false;
+        const types = type ? [type] : ["master", "self_signing", "user_signing"];
+        for (const t of types) {
+            if (!(await cacheCallbacks.getCrossSigningKeyCache?.(t))) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    /**
+     * Get cross-signing private keys from the local cache.
+     *
+     * @returns A map from key type (string) to private key (Uint8Array)
+     */
+    public async getCrossSigningKeysFromCache(): Promise<Map<string, Uint8Array>> {
+        const keys = new Map();
+        const cacheCallbacks = this.cacheCallbacks;
+        if (!cacheCallbacks) return keys;
+        for (const type of ["master", "self_signing", "user_signing"]) {
+            const privKey = await cacheCallbacks.getCrossSigningKeyCache?.(type);
+            if (!privKey) {
+                continue;
+            }
+            keys.set(type, privKey);
+        }
+        return keys;
+    }
+
+    /**
+     * Get the ID used to identify the user. This can also be used to test for
+     * the existence of a given key type.
+     *
+     * @param type - The type of key to get the ID of.  One of "master",
+     * "self_signing", or "user_signing".  Defaults to "master".
+     *
+     * @returns the ID
+     */
+    public getId(type = "master"): string | null {
+        if (!this.keys[type]) return null;
+        const keyInfo = this.keys[type];
+        return publicKeyFromKeyInfo(keyInfo);
+    }
+
+    /**
+     * Create new cross-signing keys for the given key types. The public keys
+     * will be held in this class, while the private keys are passed off to the
+     * `saveCrossSigningKeys` application callback.
+     *
+     * @param level - The key types to reset
+     */
+    public async resetKeys(level?: CrossSigningLevel): Promise<void> {
+        if (!this.callbacks.saveCrossSigningKeys) {
+            throw new Error("No saveCrossSigningKeys callback supplied");
+        }
+
+        // If we're resetting the master key, we reset all keys
+        if (level === undefined || level & CrossSigningLevel.MASTER || !this.keys.master) {
+            level = CrossSigningLevel.MASTER | CrossSigningLevel.USER_SIGNING | CrossSigningLevel.SELF_SIGNING;
+        } else if (level === (0 as CrossSigningLevel)) {
+            return;
+        }
+
+        const privateKeys: Record<string, Uint8Array> = {};
+        const keys: Record<string, ICrossSigningKey> = {};
+        let masterSigning;
+        let masterPub;
+
+        try {
+            if (level & CrossSigningLevel.MASTER) {
+                masterSigning = new global.Olm.PkSigning();
+                privateKeys.master = masterSigning.generate_seed();
+                masterPub = masterSigning.init_with_seed(privateKeys.master);
+                keys.master = {
+                    user_id: this.userId,
+                    usage: ["master"],
+                    keys: {
+                        ["ed25519:" + masterPub]: masterPub,
+                    },
+                };
+            } else {
+                [masterPub, masterSigning] = await this.getCrossSigningKey("master");
+            }
+
+            if (level & CrossSigningLevel.SELF_SIGNING) {
+                const sskSigning = new global.Olm.PkSigning();
+                try {
+                    privateKeys.self_signing = sskSigning.generate_seed();
+                    const sskPub = sskSigning.init_with_seed(privateKeys.self_signing);
+                    keys.self_signing = {
+                        user_id: this.userId,
+                        usage: ["self_signing"],
+                        keys: {
+                            ["ed25519:" + sskPub]: sskPub,
+                        },
+                    };
+                    pkSign(keys.self_signing, masterSigning, this.userId, masterPub);
+                } finally {
+                    sskSigning.free();
+                }
+            }
+
+            if (level & CrossSigningLevel.USER_SIGNING) {
+                const uskSigning = new global.Olm.PkSigning();
+                try {
+                    privateKeys.user_signing = uskSigning.generate_seed();
+                    const uskPub = uskSigning.init_with_seed(privateKeys.user_signing);
+                    keys.user_signing = {
+                        user_id: this.userId,
+                        usage: ["user_signing"],
+                        keys: {
+                            ["ed25519:" + uskPub]: uskPub,
+                        },
+                    };
+                    pkSign(keys.user_signing, masterSigning, this.userId, masterPub);
+                } finally {
+                    uskSigning.free();
+                }
+            }
+
+            Object.assign(this.keys, keys);
+            this.callbacks.saveCrossSigningKeys(privateKeys);
+        } finally {
+            if (masterSigning) {
+                masterSigning.free();
+            }
+        }
+    }
+
+    /**
+     * unsets the keys, used when another session has reset the keys, to disable cross-signing
+     */
+    public clearKeys(): void {
+        this.keys = {};
+    }
+
+    public setKeys(keys: Record<string, ICrossSigningKey>): void {
+        const signingKeys: Record<string, ICrossSigningKey> = {};
+        if (keys.master) {
+            if (keys.master.user_id !== this.userId) {
+                const error = "Mismatched user ID " + keys.master.user_id + " in master key from " + this.userId;
+                logger.error(error);
+                throw new Error(error);
+            }
+            if (!this.keys.master) {
+                // this is the first key we've seen, so first-use is true
+                this.firstUse = true;
+            } else if (publicKeyFromKeyInfo(keys.master) !== this.getId()) {
+                // this is a different key, so first-use is false
+                this.firstUse = false;
+            } // otherwise, same key, so no change
+            signingKeys.master = keys.master;
+        } else if (this.keys.master) {
+            signingKeys.master = this.keys.master;
+        } else {
+            throw new Error("Tried to set cross-signing keys without a master key");
+        }
+        const masterKey = publicKeyFromKeyInfo(signingKeys.master);
+
+        // verify signatures
+        if (keys.user_signing) {
+            if (keys.user_signing.user_id !== this.userId) {
+                const error = "Mismatched user ID " + keys.master.user_id + " in user_signing key from " + this.userId;
+                logger.error(error);
+                throw new Error(error);
+            }
+            try {
+                pkVerify(keys.user_signing, masterKey, this.userId);
+            } catch (e) {
+                logger.error("invalid signature on user-signing key");
+                // FIXME: what do we want to do here?
+                throw e;
+            }
+        }
+        if (keys.self_signing) {
+            if (keys.self_signing.user_id !== this.userId) {
+                const error = "Mismatched user ID " + keys.master.user_id + " in self_signing key from " + this.userId;
+                logger.error(error);
+                throw new Error(error);
+            }
+            try {
+                pkVerify(keys.self_signing, masterKey, this.userId);
+            } catch (e) {
+                logger.error("invalid signature on self-signing key");
+                // FIXME: what do we want to do here?
+                throw e;
+            }
+        }
+
+        // if everything checks out, then save the keys
+        if (keys.master) {
+            this.keys.master = keys.master;
+            // if the master key is set, then the old self-signing and user-signing keys are obsolete
+            delete this.keys["self_signing"];
+            delete this.keys["user_signing"];
+        }
+        if (keys.self_signing) {
+            this.keys.self_signing = keys.self_signing;
+        }
+        if (keys.user_signing) {
+            this.keys.user_signing = keys.user_signing;
+        }
+    }
+
+    public updateCrossSigningVerifiedBefore(isCrossSigningVerified: boolean): void {
+        // It is critical that this value latches forward from false to true but
+        // never back to false to avoid a downgrade attack.
+        if (!this.crossSigningVerifiedBefore && isCrossSigningVerified) {
+            this.crossSigningVerifiedBefore = true;
+        }
+    }
+
+    public async signObject<T extends object>(data: T, type: string): Promise<T & { signatures: ISignatures }> {
+        if (!this.keys[type]) {
+            throw new Error("Attempted to sign with " + type + " key but no such key present");
+        }
+        const [pubkey, signing] = await this.getCrossSigningKey(type);
+        try {
+            pkSign(data, signing, this.userId, pubkey);
+            return data as T & { signatures: ISignatures };
+        } finally {
+            signing.free();
+        }
+    }
+
+    public async signUser(key: CrossSigningInfo): Promise<ICrossSigningKey | undefined> {
+        if (!this.keys.user_signing) {
+            logger.info("No user signing key: not signing user");
+            return;
+        }
+        return this.signObject(key.keys.master, "user_signing");
+    }
+
+    public async signDevice(userId: string, device: DeviceInfo): Promise<ISignedKey | undefined> {
+        if (userId !== this.userId) {
+            throw new Error(`Trying to sign ${userId}'s device; can only sign our own device`);
+        }
+        if (!this.keys.self_signing) {
+            logger.info("No self signing key: not signing device");
+            return;
+        }
+        return this.signObject<Omit<ISignedKey, "signatures">>(
+            {
+                algorithms: device.algorithms,
+                keys: device.keys,
+                device_id: device.deviceId,
+                user_id: userId,
+            },
+            "self_signing",
+        );
+    }
+
+    /**
+     * Check whether a given user is trusted.
+     *
+     * @param userCrossSigning - Cross signing info for user
+     *
+     * @returns
+     */
+    public checkUserTrust(userCrossSigning: CrossSigningInfo): UserTrustLevel {
+        // if we're checking our own key, then it's trusted if the master key
+        // and self-signing key match
+        if (
+            this.userId === userCrossSigning.userId &&
+            this.getId() &&
+            this.getId() === userCrossSigning.getId() &&
+            this.getId("self_signing") &&
+            this.getId("self_signing") === userCrossSigning.getId("self_signing")
+        ) {
+            return new UserTrustLevel(true, true, this.firstUse);
+        }
+
+        if (!this.keys.user_signing) {
+            // If there's no user signing key, they can't possibly be verified.
+            // They may be TOFU trusted though.
+            return new UserTrustLevel(false, false, userCrossSigning.firstUse);
+        }
+
+        let userTrusted: boolean;
+        const userMaster = userCrossSigning.keys.master;
+        const uskId = this.getId("user_signing")!;
+        try {
+            pkVerify(userMaster, uskId, this.userId);
+            userTrusted = true;
+        } catch (e) {
+            userTrusted = false;
+        }
+        return new UserTrustLevel(userTrusted, userCrossSigning.crossSigningVerifiedBefore, userCrossSigning.firstUse);
+    }
+
+    /**
+     * Check whether a given device is trusted.
+     *
+     * @param userCrossSigning - Cross signing info for user
+     * @param device - The device to check
+     * @param localTrust - Whether the device is trusted locally
+     * @param trustCrossSignedDevices - Whether we trust cross signed devices
+     *
+     * @returns
+     */
+    public checkDeviceTrust(
+        userCrossSigning: CrossSigningInfo,
+        device: DeviceInfo,
+        localTrust: boolean,
+        trustCrossSignedDevices: boolean,
+    ): DeviceTrustLevel {
+        const userTrust = this.checkUserTrust(userCrossSigning);
+
+        const userSSK = userCrossSigning.keys.self_signing;
+        if (!userSSK) {
+            // if the user has no self-signing key then we cannot make any
+            // trust assertions about this device from cross-signing
+            return new DeviceTrustLevel(false, false, localTrust, trustCrossSignedDevices);
+        }
+
+        const deviceObj = deviceToObject(device, userCrossSigning.userId);
+        try {
+            // if we can verify the user's SSK from their master key...
+            pkVerify(userSSK, userCrossSigning.getId()!, userCrossSigning.userId);
+            // ...and this device's key from their SSK...
+            pkVerify(deviceObj, publicKeyFromKeyInfo(userSSK), userCrossSigning.userId);
+            // ...then we trust this device as much as far as we trust the user
+            return DeviceTrustLevel.fromUserTrustLevel(userTrust, localTrust, trustCrossSignedDevices);
+        } catch (e) {
+            return new DeviceTrustLevel(false, false, localTrust, trustCrossSignedDevices);
+        }
+    }
+
+    /**
+     * @returns Cache callbacks
+     */
+    public getCacheCallbacks(): ICacheCallbacks {
+        return this.cacheCallbacks;
+    }
+}
+
+interface DeviceObject extends IObject {
+    algorithms: string[];
+    keys: Record<string, string>;
+    device_id: string;
+    user_id: string;
+}
+
+function deviceToObject(device: DeviceInfo, userId: string): DeviceObject {
+    return {
+        algorithms: device.algorithms,
+        keys: device.keys,
+        device_id: device.deviceId,
+        user_id: userId,
+        signatures: device.signatures,
+    };
+}
+
+export enum CrossSigningLevel {
+    MASTER = 4,
+    USER_SIGNING = 2,
+    SELF_SIGNING = 1,
+}
+
+/**
+ * Represents the ways in which we trust a user
+ */
+export class UserTrustLevel {
+    public constructor(
+        private readonly crossSigningVerified: boolean,
+        private readonly crossSigningVerifiedBefore: boolean,
+        private readonly tofu: boolean,
+    ) {}
+
+    /**
+     * @returns true if this user is verified via any means
+     */
+    public isVerified(): boolean {
+        return this.isCrossSigningVerified();
+    }
+
+    /**
+     * @returns true if this user is verified via cross signing
+     */
+    public isCrossSigningVerified(): boolean {
+        return this.crossSigningVerified;
+    }
+
+    /**
+     * @returns true if we ever verified this user before (at least for
+     * the history of verifications observed by this device).
+     */
+    public wasCrossSigningVerified(): boolean {
+        return this.crossSigningVerifiedBefore;
+    }
+
+    /**
+     * @returns true if this user's key is trusted on first use
+     */
+    public isTofu(): boolean {
+        return this.tofu;
+    }
+}
+
+/**
+ * Represents the ways in which we trust a device
+ */
+export class DeviceTrustLevel {
+    public constructor(
+        public readonly crossSigningVerified: boolean,
+        public readonly tofu: boolean,
+        private readonly localVerified: boolean,
+        private readonly trustCrossSignedDevices: boolean,
+    ) {}
+
+    public static fromUserTrustLevel(
+        userTrustLevel: UserTrustLevel,
+        localVerified: boolean,
+        trustCrossSignedDevices: boolean,
+    ): DeviceTrustLevel {
+        return new DeviceTrustLevel(
+            userTrustLevel.isCrossSigningVerified(),
+            userTrustLevel.isTofu(),
+            localVerified,
+            trustCrossSignedDevices,
+        );
+    }
+
+    /**
+     * @returns true if this device is verified via any means
+     */
+    public isVerified(): boolean {
+        return Boolean(this.isLocallyVerified() || (this.trustCrossSignedDevices && this.isCrossSigningVerified()));
+    }
+
+    /**
+     * @returns true if this device is verified via cross signing
+     */
+    public isCrossSigningVerified(): boolean {
+        return this.crossSigningVerified;
+    }
+
+    /**
+     * @returns true if this device is verified locally
+     */
+    public isLocallyVerified(): boolean {
+        return this.localVerified;
+    }
+
+    /**
+     * @returns true if this device is trusted from a user's key
+     * that is trusted on first use
+     */
+    public isTofu(): boolean {
+        return this.tofu;
+    }
+}
+
+export function createCryptoStoreCacheCallbacks(store: CryptoStore, olmDevice: OlmDevice): ICacheCallbacks {
+    return {
+        getCrossSigningKeyCache: async function (
+            type: keyof SecretStorePrivateKeys,
+            _expectedPublicKey: string,
+        ): Promise<Uint8Array> {
+            const key = await new Promise<any>((resolve) => {
+                return store.doTxn("readonly", [IndexedDBCryptoStore.STORE_ACCOUNT], (txn) => {
+                    store.getSecretStorePrivateKey(txn, resolve, type);
+                });
+            });
+
+            if (key && key.ciphertext) {
+                const pickleKey = Buffer.from(olmDevice.pickleKey);
+                const decrypted = await decryptAES(key, pickleKey, type);
+                return decodeBase64(decrypted);
+            } else {
+                return key;
+            }
+        },
+        storeCrossSigningKeyCache: async function (
+            type: keyof SecretStorePrivateKeys,
+            key?: Uint8Array,
+        ): Promise<void> {
+            if (!(key instanceof Uint8Array)) {
+                throw new Error(`storeCrossSigningKeyCache expects Uint8Array, got ${key}`);
+            }
+            const pickleKey = Buffer.from(olmDevice.pickleKey);
+            const encryptedKey = await encryptAES(encodeBase64(key), pickleKey, type);
+            return store.doTxn("readwrite", [IndexedDBCryptoStore.STORE_ACCOUNT], (txn) => {
+                store.storeSecretStorePrivateKey(txn, type, encryptedKey);
+            });
+        },
+    };
+}
+
+export type KeysDuringVerification = [[string, PkSigning], [string, PkSigning], [string, PkSigning], void];
+
+/**
+ * Request cross-signing keys from another device during verification.
+ *
+ * @param baseApis - base Matrix API interface
+ * @param userId - The user ID being verified
+ * @param deviceId - The device ID being verified
+ */
+export async function requestKeysDuringVerification(
+    baseApis: MatrixClient,
+    userId: string,
+    deviceId: string,
+): Promise<KeysDuringVerification | void> {
+    // If this is a self-verification, ask the other party for keys
+    if (baseApis.getUserId() !== userId) {
+        return;
+    }
+    logger.log("Cross-signing: Self-verification done; requesting keys");
+    // This happens asynchronously, and we're not concerned about waiting for
+    // it. We return here in order to test.
+    return new Promise<KeysDuringVerification | void>((resolve, reject) => {
+        const client = baseApis;
+        const original = client.crypto!.crossSigningInfo;
+
+        // We already have all of the infrastructure we need to validate and
+        // cache cross-signing keys, so instead of replicating that, here we set
+        // up callbacks that request them from the other device and call
+        // CrossSigningInfo.getCrossSigningKey() to validate/cache
+        const crossSigning = new CrossSigningInfo(
+            original.userId,
+            {
+                getCrossSigningKey: async (type): Promise<Uint8Array> => {
+                    logger.debug("Cross-signing: requesting secret", type, deviceId);
+                    const { promise } = client.requestSecret(`m.cross_signing.${type}`, [deviceId]);
+                    const result = await promise;
+                    const decoded = decodeBase64(result);
+                    return Uint8Array.from(decoded);
+                },
+            },
+            original.getCacheCallbacks(),
+        );
+        crossSigning.keys = original.keys;
+
+        // XXX: get all keys out if we get one key out
+        // https://github.com/vector-im/element-web/issues/12604
+        // then change here to reject on the timeout
+        // Requests can be ignored, so don't wait around forever
+        const timeout = new Promise<void>((resolve) => {
+            setTimeout(resolve, KEY_REQUEST_TIMEOUT_MS, new Error("Timeout"));
+        });
+
+        // also request and cache the key backup key
+        const backupKeyPromise = (async (): Promise<void> => {
+            const cachedKey = await client.crypto!.getSessionBackupPrivateKey();
+            if (!cachedKey) {
+                logger.info("No cached backup key found. Requesting...");
+                const secretReq = client.requestSecret("m.megolm_backup.v1", [deviceId]);
+                const base64Key = await secretReq.promise;
+                logger.info("Got key backup key, decoding...");
+                const decodedKey = decodeBase64(base64Key);
+                logger.info("Decoded backup key, storing...");
+                await client.crypto!.storeSessionBackupPrivateKey(Uint8Array.from(decodedKey));
+                logger.info("Backup key stored. Starting backup restore...");
+                const backupInfo = await client.getKeyBackupVersion();
+                // no need to await for this - just let it go in the bg
+                client.restoreKeyBackupWithCache(undefined, undefined, backupInfo!).then(() => {
+                    logger.info("Backup restored.");
+                });
+            }
+        })();
+
+        // We call getCrossSigningKey() for its side-effects
+        return Promise.race<KeysDuringVerification | void>([
+            Promise.all([
+                crossSigning.getCrossSigningKey("master"),
+                crossSigning.getCrossSigningKey("self_signing"),
+                crossSigning.getCrossSigningKey("user_signing"),
+                backupKeyPromise,
+            ]) as Promise<KeysDuringVerification>,
+            timeout,
+        ]).then(resolve, reject);
+    }).catch((e) => {
+        logger.warn("Cross-signing: failure while requesting keys:", e);
+    });
+}