Adding upstream version 110.0.1.upstream/110.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 753 insertions, 0 deletions

diff --git a/services/fxaccounts/FxAccountsKeys.jsm b/services/fxaccounts/FxAccountsKeys.jsm
new file mode 100644
index 0000000000..a27b53eb7c
--- /dev/null
+++ b/services/fxaccounts/FxAccountsKeys.jsm
@@ -0,0 +1,753 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+"use strict";
+
+const { PromiseUtils } = ChromeUtils.importESModule(
+  "resource://gre/modules/PromiseUtils.sys.mjs"
+);
+const { CommonUtils } = ChromeUtils.import(
+  "resource://services-common/utils.js"
+);
+
+const { CryptoUtils } = ChromeUtils.import(
+  "resource://services-crypto/utils.js"
+);
+
+const {
+  LEGACY_DERIVED_KEYS_NAMES,
+  SCOPE_OLD_SYNC,
+  LEGACY_SCOPE_WEBEXT_SYNC,
+  DEPRECATED_SCOPE_ECOSYSTEM_TELEMETRY,
+  FX_OAUTH_CLIENT_ID,
+  log,
+  logPII,
+} = ChromeUtils.import("resource://gre/modules/FxAccountsCommon.js");
+
+// These are the scopes that correspond to new storage for the `LEGACY_DERIVED_KEYS_NAMES`.
+// We will, if necessary, migrate storage for those keys so that it's associated with
+// these scopes.
+const LEGACY_DERIVED_KEY_SCOPES = [SCOPE_OLD_SYNC, LEGACY_SCOPE_WEBEXT_SYNC];
+
+// These are scopes that we used to store, but are no longer using,
+// and hence should be deleted from storage if present.
+const DEPRECATED_KEY_SCOPES = [DEPRECATED_SCOPE_ECOSYSTEM_TELEMETRY];
+
+/**
+ * Utilities for working with key material linked to the user's account.
+ *
+ * Each Firefox Account has 32 bytes of root key material called `kB` which is
+ * linked to the user's password, and which is used to derive purpose-specific
+ * subkeys for things like encrypting the user's sync data. This class provides
+ * the interface for working with such key material.
+ *
+ * Most recent FxA clients obtain appropriate key material directly as part of
+ * their sign-in flow, using a special extension of the OAuth2.0 protocol to
+ * securely deliver the derived keys without revealing `kB`. Keys obtained in
+ * in this way are called "scoped keys" since each corresponds to a particular
+ * OAuth scope, and this class provides a `getKeyForScope` method that is the
+ * preferred method for consumers to work with such keys.
+ *
+ * However, since the FxA integration in Firefox Desktop pre-dates the use of
+ * OAuth2.0, we also have a lot of code for fetching keys via an older flow.
+ * This flow uses a special `keyFetchToken` to obtain `kB` and then derive various
+ * sub-keys from it. Consumers should consider this an internal implementation
+ * detail of the `FxAccountsKeys` class and should prefer `getKeyForScope` where
+ * possible.  We intend to remove support for Firefox ever directly handling `kB`
+ * at some point in the future.
+ */
+class FxAccountsKeys {
+  constructor(fxAccountsInternal) {
+    this._fxai = fxAccountsInternal;
+  }
+
+  /**
+   * Checks if we currently have the key for a given scope, or if we have enough to
+   * be able to successfully fetch and unwrap it for the signed-in-user.
+   *
+   * Unlike `getKeyForScope`, this will not hit the network to fetch wrapped keys if
+   * they aren't available locally.
+   */
+  canGetKeyForScope(scope) {
+    return this._fxai.withCurrentAccountState(async currentState => {
+      let userData = await currentState.getUserAccountData();
+      if (!userData) {
+        throw new Error("Can't possibly get keys; User is not signed in");
+      }
+      if (!userData.verified) {
+        log.info("Can't get keys; user is not verified");
+        return false;
+      }
+
+      if (userData.scopedKeys && userData.scopedKeys.hasOwnProperty(scope)) {
+        return true;
+      }
+
+      // For sync-related scopes, we might have stored the keys in a legacy format.
+      if (scope == SCOPE_OLD_SYNC) {
+        if (userData.kSync && userData.kXCS) {
+          return true;
+        }
+      }
+      if (scope == LEGACY_SCOPE_WEBEXT_SYNC) {
+        if (userData.kExtSync && userData.kExtKbHash) {
+          return true;
+        }
+      }
+
+      // `kB` is deprecated, but if we have it, we can use it to derive any scoped key.
+      if (userData.kB) {
+        return true;
+      }
+
+      // If we have a `keyFetchToken` we can fetch `kB`.
+      if (userData.keyFetchToken) {
+        return true;
+      }
+
+      log.info("Can't get keys; no key material or tokens available");
+      return false;
+    });
+  }
+
+  /**
+   * Get the key for a specified OAuth scope.
+   *
+   * @param {String} scope The OAuth scope whose key should be returned
+   *
+   * @return Promise<JWK>
+   *        If no key is available the promise resolves to `null`.
+   *        If a key is available for the given scope, th promise resolves to a JWK with fields:
+   *        {
+   *          scope: The requested scope
+   *          kid: Key identifier
+   *          k: Derived key material
+   *          kty: Always "oct" for scoped keys
+   *        }
+   *
+   */
+  async getKeyForScope(scope) {
+    const { scopedKeys } = await this._loadOrFetchKeys();
+    if (!scopedKeys.hasOwnProperty(scope)) {
+      throw new Error(`Key not available for scope "${scope}"`);
+    }
+    return {
+      scope,
+      ...scopedKeys[scope],
+    };
+  }
+
+  /**
+   * Format a JWK key material as hex rather than base64.
+   *
+   * This is a backwards-compatibility helper for code that needs raw key bytes rather
+   * than the JWK format offered by FxA scopes keys.
+   *
+   * @param {Object} jwk The JWK from which to extract the `k` field as hex.
+   *
+   */
+  keyAsHex(jwk) {
+    return CommonUtils.base64urlToHex(jwk.k);
+  }
+
+  /**
+   * Format a JWK kid as hex rather than base64.
+   *
+   * This is a backwards-compatibility helper for code that needs a raw key fingerprint
+   * for use as a key identifier, rather than the timestamp+fingerprint format used by
+   * FxA scoped keys.
+   *
+   * @param {Object} jwk The JWK from which to extract the `kid` field as hex.
+   */
+  kidAsHex(jwk) {
+    // The kid format is "{timestamp}-{b64url(fingerprint)}", but we have to be careful
+    // because the fingerprint component may contain "-" as well, and we want to ensure
+    // the timestamp component was non-empty.
+    const idx = jwk.kid.indexOf("-") + 1;
+    if (idx <= 1) {
+      throw new Error(`Invalid kid: ${jwk.kid}`);
+    }
+    return CommonUtils.base64urlToHex(jwk.kid.slice(idx));
+  }
+
+  /**
+   * Fetch encryption keys for the signed-in-user from the FxA API server.
+   *
+   * Not for user consumption.  Exists to cause the keys to be fetched.
+   *
+   * Returns user data so that it can be chained with other methods.
+   *
+   * @return Promise
+   *        The promise resolves to the credentials object of the signed-in user:
+   *        {
+   *          email: The user's email address
+   *          uid: The user's unique id
+   *          sessionToken: Session for the FxA server
+   *          scopedKeys: Object mapping OAuth scopes to corresponding derived keys
+   *          kSync: An encryption key for Sync
+   *          kXCS: A key hash of kB for the X-Client-State header
+   *          kExtSync: An encryption key for WebExtensions syncing
+   *          kExtKbHash: A key hash of kB for WebExtensions syncing
+   *          verified: email verification status
+   *        }
+   * @throws If there is no user signed in.
+   */
+  async _loadOrFetchKeys() {
+    return this._fxai.withCurrentAccountState(async currentState => {
+      try {
+        let userData = await currentState.getUserAccountData();
+        if (!userData) {
+          throw new Error("Can't get keys; User is not signed in");
+        }
+        // If we have all the keys in latest storage location, we're good.
+        if (userData.scopedKeys) {
+          if (
+            LEGACY_DERIVED_KEY_SCOPES.every(scope =>
+              userData.scopedKeys.hasOwnProperty(scope)
+            ) &&
+            !DEPRECATED_KEY_SCOPES.some(scope =>
+              userData.scopedKeys.hasOwnProperty(scope)
+            )
+          ) {
+            return userData;
+          }
+        }
+        // If not, we've got work to do, and we debounce to avoid duplicating it.
+        if (!currentState.whenKeysReadyDeferred) {
+          currentState.whenKeysReadyDeferred = PromiseUtils.defer();
+          // N.B. we deliberately don't `await` here, and instead use the promise
+          // to resolve `whenKeysReadyDeferred` (which we then `await` below).
+          this._migrateOrFetchKeys(currentState, userData).then(
+            dataWithKeys => {
+              currentState.whenKeysReadyDeferred.resolve(dataWithKeys);
+              currentState.whenKeysReadyDeferred = null;
+            },
+            err => {
+              currentState.whenKeysReadyDeferred.reject(err);
+              currentState.whenKeysReadyDeferred = null;
+            }
+          );
+        }
+        return await currentState.whenKeysReadyDeferred.promise;
+      } catch (err) {
+        return this._fxai._handleTokenError(err);
+      }
+    });
+  }
+
+  /**
+   * Key storage migration or fetching logic.
+   *
+   * This method contains the doing-expensive-operations part of the logic of
+   * _loadOrFetchKeys(), factored out into a separate method so we can debounce it.
+   *
+   */
+  async _migrateOrFetchKeys(currentState, userData) {
+    // Bug 1697596 - delete any deprecated scoped keys from storage.
+    // If any of the deprecated keys are present, then we know that we've
+    // previously applied all the other migrations below, otherwise there
+    // would not be any `scopedKeys` field.
+    if (userData.scopedKeys) {
+      const toRemove = DEPRECATED_KEY_SCOPES.filter(scope =>
+        userData.scopedKeys.hasOwnProperty(scope)
+      );
+      if (toRemove.length) {
+        for (const scope of toRemove) {
+          delete userData.scopedKeys[scope];
+        }
+        await currentState.updateUserAccountData({
+          scopedKeys: userData.scopedKeys,
+          // Prior to deprecating SCOPE_ECOSYSTEM_TELEMETRY, this file had some
+          // special code to store it as a top-level user data field. So, this
+          // file also gets to delete it as part of the deprecation.
+          ecosystemUserId: null,
+          ecosystemAnonId: null,
+        });
+        userData = await currentState.getUserAccountData();
+        return userData;
+      }
+    }
+    // Bug 1661407 - migrate from legacy storage of keys as top-level account
+    // data fields, to storing them as scoped keys in the `scopedKeys` object.
+    if (
+      LEGACY_DERIVED_KEYS_NAMES.every(name => userData.hasOwnProperty(name))
+    ) {
+      log.info("Migrating from legacy key fields to scopedKeys.");
+      const scopedKeys = userData.scopedKeys || {};
+      await currentState.updateUserAccountData({
+        scopedKeys: {
+          ...scopedKeys,
+          ...(await this._deriveScopedKeysFromAccountData(userData)),
+        },
+      });
+      userData = await currentState.getUserAccountData();
+      return userData;
+    }
+    // Bug 1426306 - Migrate from kB to derived keys.
+    if (userData.kB) {
+      log.info("Migrating kB to derived keys.");
+      const { uid, kB, sessionToken } = userData;
+      const scopedKeysMetadata = await this._fetchScopedKeysMetadata(
+        sessionToken
+      );
+      await currentState.updateUserAccountData({
+        uid,
+        ...(await this._deriveKeys(
+          uid,
+          CommonUtils.hexToBytes(kB),
+          scopedKeysMetadata
+        )),
+        kA: null, // Remove kA and kB from storage.
+        kB: null,
+      });
+      userData = await currentState.getUserAccountData();
+      return userData;
+    }
+    // Otherwise, we need to fetch from the network and unwrap.
+    if (!userData.sessionToken) {
+      throw new Error("No sessionToken");
+    }
+    if (!userData.keyFetchToken) {
+      throw new Error("No keyFetchToken");
+    }
+    return this._fetchAndUnwrapAndDeriveKeys(
+      currentState,
+      userData.sessionToken,
+      userData.keyFetchToken
+    );
+  }
+
+  /**
+   * Fetch keys from the server, unwrap them, and derive required sub-keys.
+   *
+   * Once the user's email is verified, we can resquest the root key `kB` from the
+   * FxA server, unwrap it using the client-side secret `unwrapBKey`, and then
+   * derive all the sub-keys required for operation of the browser.
+   */
+  async _fetchAndUnwrapAndDeriveKeys(
+    currentState,
+    sessionToken,
+    keyFetchToken
+  ) {
+    if (logPII) {
+      log.debug(
+        `fetchAndUnwrapKeys: sessionToken: ${sessionToken}, keyFetchToken: ${keyFetchToken}`
+      );
+    }
+
+    // Sign out if we don't have the necessary tokens.
+    if (!sessionToken || !keyFetchToken) {
+      // this seems really bad and we should remove this - bug 1572313.
+      log.warn("improper _fetchAndUnwrapKeys() call: token missing");
+      await this._fxai.signOut();
+      return null;
+    }
+
+    // Deriving OAuth scoped keys requires additional metadata from the server.
+    // We fetch this first, before fetching the actual key material, because the
+    // keyFetchToken is single-use and we don't want to do a potentially-fallible
+    // operation after consuming it.
+    const scopedKeysMetadata = await this._fetchScopedKeysMetadata(
+      sessionToken
+    );
+
+    // Fetch the wrapped keys.
+    // It would be nice to be able to fetch this in a single operation with fetching
+    // the metadata above, but that requires server-side changes in FxA.
+    let { wrapKB } = await this._fetchKeys(keyFetchToken);
+
+    let data = await currentState.getUserAccountData();
+
+    // Sanity check that the user hasn't changed out from under us (which should
+    // be impossible given this is called within _withCurrentAccountState, but...)
+    if (data.keyFetchToken !== keyFetchToken) {
+      throw new Error("Signed in user changed while fetching keys!");
+    }
+
+    let kBbytes = CryptoUtils.xor(
+      CommonUtils.hexToBytes(data.unwrapBKey),
+      wrapKB
+    );
+
+    if (logPII) {
+      log.debug("kBbytes: " + kBbytes);
+    }
+
+    let updateData = {
+      ...(await this._deriveKeys(data.uid, kBbytes, scopedKeysMetadata)),
+      keyFetchToken: null, // null values cause the item to be removed.
+      unwrapBKey: null,
+    };
+
+    if (logPII) {
+      log.debug(`Keys Obtained: ${updateData.scopedKeys}`);
+    } else {
+      log.debug(
+        "Keys Obtained: " + Object.keys(updateData.scopedKeys).join(", ")
+      );
+    }
+
+    // Just double-check that we derived all the right stuff.
+    const EXPECTED_FIELDS = LEGACY_DERIVED_KEYS_NAMES.concat(["scopedKeys"]);
+    if (EXPECTED_FIELDS.some(k => !updateData[k])) {
+      const missing = EXPECTED_FIELDS.filter(k => !updateData[k]);
+      throw new Error(`user data missing: ${missing.join(", ")}`);
+    }
+
+    await currentState.updateUserAccountData(updateData);
+    return currentState.getUserAccountData();
+  }
+
+  /**
+   * Fetch the wrapped root key `wrapKB` from the FxA server.
+   *
+   * This consumes the single-use `keyFetchToken`.
+   */
+  _fetchKeys(keyFetchToken) {
+    let client = this._fxai.fxAccountsClient;
+    log.debug(
+      `Fetching keys with token ${!!keyFetchToken} from ${client.host}`
+    );
+    if (logPII) {
+      log.debug("fetchKeys - the token is " + keyFetchToken);
+    }
+    return client.accountKeys(keyFetchToken);
+  }
+
+  /**
+   * Fetch additional metadata required for deriving scoped keys.
+   *
+   * This includes timestamps and a server-provided secret to mix in to
+   * the derived value in order to support key rotation.
+   */
+  async _fetchScopedKeysMetadata(sessionToken) {
+    // Hard-coded list of scopes that we know about.
+    // This list will probably grow in future.
+    // Note that LEGACY_SCOPE_WEBEXT_SYNC is not in this list, it gets special-case handling below.
+    const scopes = [SCOPE_OLD_SYNC].join(" ");
+    const scopedKeysMetadata = await this._fxai.fxAccountsClient.getScopedKeyData(
+      sessionToken,
+      FX_OAUTH_CLIENT_ID,
+      scopes
+    );
+    // The server may decline us permission for some of those scopes, although it really shouldn't.
+    // We can live without them...except for the OLDSYNC scope, whose absence would be catastrophic.
+    if (!scopedKeysMetadata.hasOwnProperty(SCOPE_OLD_SYNC)) {
+      log.warn(
+        "The FxA server did not grant Firefox the `oldsync` scope; this is most unexpected!" +
+          ` scopes were: ${Object.keys(scopedKeysMetadata)}`
+      );
+      throw new Error(
+        "The FxA server did not grant Firefox the `oldsync` scope"
+      );
+    }
+    // Firefox Desktop invented its own special scope for legacy webextension syncing,
+    // with its own special key. Rather than teach the rest of FxA about this scope
+    // that will never be used anywhere else, just give it the same metadata as
+    // the main sync scope. This can go away once legacy webext sync is removed.
+    // (ref Bug 1637465 for tracking that removal)
+    scopedKeysMetadata[LEGACY_SCOPE_WEBEXT_SYNC] = {
+      ...scopedKeysMetadata[SCOPE_OLD_SYNC],
+      identifier: LEGACY_SCOPE_WEBEXT_SYNC,
+    };
+    return scopedKeysMetadata;
+  }
+
+  /**
+   * Derive purpose-specific keys from the root FxA key `kB`.
+   *
+   * Everything that uses an encryption key from FxA uses a purpose-specific derived
+   * key. For new uses this is derived in a structured way based on OAuth scopes,
+   * while for legacy uses (mainly Firefox Sync) it is derived in a more ad-hoc fashion.
+   * This method does all the derivations for the uses that we know about.
+   *
+   */
+  async _deriveKeys(uid, kBbytes, scopedKeysMetadata) {
+    const scopedKeys = await this._deriveScopedKeys(
+      uid,
+      kBbytes,
+      scopedKeysMetadata
+    );
+    return {
+      scopedKeys,
+      // Existing browser code might expect sync keys to be available as top-level account data.
+      // For b/w compat we can derive these even if they're not in our list of scoped keys for
+      // some reason (since the derivation doesn't depend on server-provided data).
+      kSync: scopedKeys[SCOPE_OLD_SYNC]
+        ? this.keyAsHex(scopedKeys[SCOPE_OLD_SYNC])
+        : CommonUtils.bytesAsHex(await this._deriveSyncKey(kBbytes)),
+      kXCS: scopedKeys[SCOPE_OLD_SYNC]
+        ? this.kidAsHex(scopedKeys[SCOPE_OLD_SYNC])
+        : CommonUtils.bytesAsHex(await this._deriveXClientState(kBbytes)),
+      kExtSync: scopedKeys[LEGACY_SCOPE_WEBEXT_SYNC]
+        ? this.keyAsHex(scopedKeys[LEGACY_SCOPE_WEBEXT_SYNC])
+        : CommonUtils.bytesAsHex(await this._deriveWebExtSyncStoreKey(kBbytes)),
+      kExtKbHash: scopedKeys[LEGACY_SCOPE_WEBEXT_SYNC]
+        ? this.kidAsHex(scopedKeys[LEGACY_SCOPE_WEBEXT_SYNC])
+        : CommonUtils.bytesAsHex(await this._deriveWebExtKbHash(uid, kBbytes)),
+    };
+  }
+
+  /**
+   * Derive various scoped keys from the root FxA key `kB`.
+   *
+   * The `scopedKeysMetadata` object is additional information fetched from the server that
+   * that gets mixed in to the key derivation, with each member of the object corresponding
+   * to an OAuth scope that keys its own scoped key.
+   *
+   * As a special case for backwards-compatibility, sync-related scopes get special
+   * treatment to use a legacy derivation algorithm.
+   *
+   */
+  async _deriveScopedKeys(uid, kBbytes, scopedKeysMetadata) {
+    const scopedKeys = {};
+    for (const scope in scopedKeysMetadata) {
+      if (LEGACY_DERIVED_KEY_SCOPES.includes(scope)) {
+        scopedKeys[scope] = await this._deriveLegacyScopedKey(
+          uid,
+          kBbytes,
+          scope,
+          scopedKeysMetadata[scope]
+        );
+      } else {
+        scopedKeys[scope] = await this._deriveScopedKey(
+          uid,
+          kBbytes,
+          scope,
+          scopedKeysMetadata[scope]
+        );
+      }
+    }
+    return scopedKeys;
+  }
+
+  /**
+   * Derive the `scopedKeys` data field based on current account data.
+   *
+   * This is a backwards-compatibility convenience for users who are already signed in to Firefox
+   * and have legacy fields like `kSync` and `kXCS` in their top-level account data, but do not have
+   * the newer `scopedKeys` field. We populate it with the scoped keys for sync and webext-sync.
+   *
+   */
+  async _deriveScopedKeysFromAccountData(userData) {
+    const scopedKeysMetadata = await this._fetchScopedKeysMetadata(
+      userData.sessionToken
+    );
+    const scopedKeys = userData.scopedKeys || {};
+    for (const scope of LEGACY_DERIVED_KEY_SCOPES) {
+      if (scopedKeysMetadata.hasOwnProperty(scope)) {
+        let kid, key;
+        if (scope == SCOPE_OLD_SYNC) {
+          ({ kXCS: kid, kSync: key } = userData);
+        } else if (scope == LEGACY_SCOPE_WEBEXT_SYNC) {
+          ({ kExtKbHash: kid, kExtSync: key } = userData);
+        } else {
+          // Should never happen, but a nice internal consistency check.
+          throw new Error(`Unexpected legacy key-bearing scope: ${scope}`);
+        }
+        if (!kid || !key) {
+          throw new Error(
+            `Account is missing legacy key fields for scope: ${scope}`
+          );
+        }
+        scopedKeys[scope] = await this._formatLegacyScopedKey(
+          CommonUtils.hexToArrayBuffer(kid),
+          CommonUtils.hexToArrayBuffer(key),
+          scope,
+          scopedKeysMetadata[scope]
+        );
+      }
+    }
+    return scopedKeys;
+  }
+
+  /**
+   * Derive a scoped key for an individual OAuth scope.
+   *
+   * The derivation here uses HKDF to combine:
+   *   - the root key material kB
+   *   - a unique identifier for this scoped key
+   *   - a server-provided secret that allows for key rotation
+   *   - the account uid as an additional salt
+   *
+   * It produces 32 bytes of (secret) key material along with a (potentially public)
+   * key identifier, formatted as a JWK.
+   *
+   * The full details are in the technical docs at
+   * https://docs.google.com/document/d/1IvQJFEBFz0PnL4uVlIvt8fBS_IPwSK-avK0BRIHucxQ/
+   */
+  async _deriveScopedKey(uid, kBbytes, scope, scopedKeyMetadata) {
+    kBbytes = CommonUtils.byteStringToArrayBuffer(kBbytes);
+
+    const FINGERPRINT_LENGTH = 16;
+    const KEY_LENGTH = 32;
+    const VALID_UID = /^[0-9a-f]{32}$/i;
+    const VALID_ROTATION_SECRET = /^[0-9a-f]{64}$/i;
+
+    // Engage paranoia mode for input data.
+    if (!VALID_UID.test(uid)) {
+      throw new Error("uid must be a 32-character hex string");
+    }
+    if (kBbytes.length != 32) {
+      throw new Error("kBbytes must be exactly 32 bytes");
+    }
+    if (
+      typeof scopedKeyMetadata.identifier !== "string" ||
+      scopedKeyMetadata.identifier.length < 10
+    ) {
+      throw new Error("identifier must be a string of length >= 10");
+    }
+    if (typeof scopedKeyMetadata.keyRotationTimestamp !== "number") {
+      throw new Error("keyRotationTimestamp must be a number");
+    }
+    if (!VALID_ROTATION_SECRET.test(scopedKeyMetadata.keyRotationSecret)) {
+      throw new Error("keyRotationSecret must be a 64-character hex string");
+    }
+
+    // The server returns milliseconds, we want seconds as a string.
+    const keyRotationTimestamp =
+      "" + Math.round(scopedKeyMetadata.keyRotationTimestamp / 1000);
+    if (keyRotationTimestamp.length < 10) {
+      throw new Error("keyRotationTimestamp must round to a 10-digit number");
+    }
+
+    const keyRotationSecret = CommonUtils.hexToArrayBuffer(
+      scopedKeyMetadata.keyRotationSecret
+    );
+    const salt = CommonUtils.hexToArrayBuffer(uid);
+    const context = new TextEncoder("utf8").encode(
+      "identity.mozilla.com/picl/v1/scoped_key\n" + scopedKeyMetadata.identifier
+    );
+
+    const inputKey = new Uint8Array(64);
+    inputKey.set(kBbytes, 0);
+    inputKey.set(keyRotationSecret, 32);
+
+    const derivedKeyMaterial = await CryptoUtils.hkdf(
+      inputKey,
+      salt,
+      context,
+      FINGERPRINT_LENGTH + KEY_LENGTH
+    );
+    const fingerprint = derivedKeyMaterial.slice(0, FINGERPRINT_LENGTH);
+    const key = derivedKeyMaterial.slice(
+      FINGERPRINT_LENGTH,
+      FINGERPRINT_LENGTH + KEY_LENGTH
+    );
+
+    return {
+      kid:
+        keyRotationTimestamp +
+        "-" +
+        ChromeUtils.base64URLEncode(fingerprint, {
+          pad: false,
+        }),
+      k: ChromeUtils.base64URLEncode(key, {
+        pad: false,
+      }),
+      kty: "oct",
+    };
+  }
+
+  /**
+   * Derive the scoped key for the one of our legacy sync-related scopes.
+   *
+   * These uses a different key-derivation algoritm that incorporates less server-provided
+   * data, for backwards-compatibility reasons.
+   *
+   */
+  async _deriveLegacyScopedKey(uid, kBbytes, scope, scopedKeyMetadata) {
+    let kid, key;
+    if (scope == SCOPE_OLD_SYNC) {
+      kid = await this._deriveXClientState(kBbytes);
+      key = await this._deriveSyncKey(kBbytes);
+    } else if (scope == LEGACY_SCOPE_WEBEXT_SYNC) {
+      kid = await this._deriveWebExtKbHash(uid, kBbytes);
+      key = await this._deriveWebExtSyncStoreKey(kBbytes);
+    } else {
+      throw new Error(`Unexpected legacy key-bearing scope: ${scope}`);
+    }
+    kid = CommonUtils.byteStringToArrayBuffer(kid);
+    key = CommonUtils.byteStringToArrayBuffer(key);
+    return this._formatLegacyScopedKey(kid, key, scope, scopedKeyMetadata);
+  }
+
+  /**
+   * Format key material for a legacy scyne-related scope as a JWK.
+   *
+   * @param {ArrayBuffer} kid bytes of the key hash to use in the key identifier
+   * @param {ArrayBuffer} key bytes of the derived sync key
+   * @param {String} scope the scope with which this key is associated
+   * @param {Number} keyRotationTimestamp server-provided timestamp of last key rotation
+   * @returns {Object} key material formatted as a JWK object
+   */
+  _formatLegacyScopedKey(kid, key, scope, { keyRotationTimestamp }) {
+    kid = ChromeUtils.base64URLEncode(kid, {
+      pad: false,
+    });
+    key = ChromeUtils.base64URLEncode(key, {
+      pad: false,
+    });
+    return {
+      kid: `${keyRotationTimestamp}-${kid}`,
+      k: key,
+      kty: "oct",
+    };
+  }
+
+  /**
+   * Derive the Sync Key given the byte string kB.
+   *
+   * @returns Promise<HKDF(kB, undefined, "identity.mozilla.com/picl/v1/oldsync", 64)>
+   */
+  async _deriveSyncKey(kBbytes) {
+    return CryptoUtils.hkdfLegacy(
+      kBbytes,
+      undefined,
+      "identity.mozilla.com/picl/v1/oldsync",
+      2 * 32
+    );
+  }
+
+  /**
+   * Derive the X-Client-State header given the byte string kB.
+   *
+   * @returns Promise<SHA256(kB)[:16]>
+   */
+  async _deriveXClientState(kBbytes) {
+    return this._sha256(kBbytes).slice(0, 16);
+  }
+
+  /**
+   * Derive the WebExtensions Sync Storage Key given the byte string kB.
+   *
+   * @returns Promise<HKDF(kB, undefined, "identity.mozilla.com/picl/v1/chrome.storage.sync", 64)>
+   */
+  async _deriveWebExtSyncStoreKey(kBbytes) {
+    return CryptoUtils.hkdfLegacy(
+      kBbytes,
+      undefined,
+      "identity.mozilla.com/picl/v1/chrome.storage.sync",
+      2 * 32
+    );
+  }
+
+  /**
+   * Derive the WebExtensions kbHash given the byte string kB.
+   *
+   * @returns Promise<SHA256(uid + kB)>
+   */
+  async _deriveWebExtKbHash(uid, kBbytes) {
+    return this._sha256(uid + kBbytes);
+  }
+
+  _sha256(bytes) {
+    let hasher = Cc["@mozilla.org/security/hash;1"].createInstance(
+      Ci.nsICryptoHash
+    );
+    hasher.init(hasher.SHA256);
+    return CryptoUtils.digestBytes(bytes, hasher);
+  }
+}
+
+var EXPORTED_SYMBOLS = ["FxAccountsKeys"];