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Diffstat (limited to '')
| -rw-r--r-- | services/fxaccounts/FxAccountsKeys.sys.mjs | 649 |
1 files changed, 649 insertions, 0 deletions
diff --git a/services/fxaccounts/FxAccountsKeys.sys.mjs b/services/fxaccounts/FxAccountsKeys.sys.mjs new file mode 100644 index 0000000000..ad19df31be --- /dev/null +++ b/services/fxaccounts/FxAccountsKeys.sys.mjs @@ -0,0 +1,649 @@ +/* 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/. */ + +import { CommonUtils } from "resource://services-common/utils.sys.mjs"; + +import { CryptoUtils } from "resource://services-crypto/utils.sys.mjs"; + +import { + SCOPE_OLD_SYNC, + DEPRECATED_SCOPE_ECOSYSTEM_TELEMETRY, + FX_OAUTH_CLIENT_ID, + log, + logPII, +} from "resource://gre/modules/FxAccountsCommon.sys.mjs"; + +// The following top-level fields have since been deprecated and exist here purely +// to be removed from the account state when seen. After a reasonable period of time +// has passed, where users have been migrated away from those keys they should be safe to be removed +const DEPRECATED_DERIVED_KEYS_NAMES = [ + "kSync", + "kXCS", + "kExtSync", + "kExtKbHash", + "ecosystemUserId", + "ecosystemAnonId", +]; + +// This scope and its associated key material were used by the old Kinto webextension +// storage backend, but has since been decommissioned. It's here entirely so that we +// remove the corresponding key from storage if present. We should be safe to remove it +// after some sensible period of time has elapsed to allow most clients to update. +const DEPRECATED_SCOPE_WEBEXT_SYNC = "sync:addon_storage"; + +// 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]; + +// 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, + DEPRECATED_SCOPE_WEBEXT_SYNC, +]; + +/** + * 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. + */ +export 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; + } + + // 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 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 + * 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) + ) && + !DEPRECATED_DERIVED_KEYS_NAMES.some(keyName => + userData.hasOwnProperty(keyName) + ) + ) { + return userData; + } + } + // If not, we've got work to do, and we debounce to avoid duplicating it. + if (!currentState.whenKeysReadyDeferred) { + currentState.whenKeysReadyDeferred = Promise.withResolvers(); + // 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); + } + }); + } + + /** + * Set externally derived scoped keys in internal storage + * @param { Object } scopedKeys: The scoped keys object derived by the oauth flow + * + * @return { Promise }: A promise that resolves if the keys were successfully stored, + * or rejects if we failed to persist the keys, or if the user is not signed in already + */ + async setScopedKeys(scopedKeys) { + return this._fxai.withCurrentAccountState(async currentState => { + const userData = await currentState.getUserAccountData(); + if (!userData) { + throw new Error("Cannot persist keys, no user signed in"); + } + await currentState.updateUserAccountData({ + scopedKeys, + }); + }); + } + + /** + * 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) { + // If the required scopes are present in `scopedKeys`, then we know that we've + // previously applied all earlier migrations + // so we are safe to delete deprecated fields that older migrations + // might have depended on. + if ( + userData.scopedKeys && + LEGACY_DERIVED_KEY_SCOPES.every(scope => + userData.scopedKeys.hasOwnProperty(scope) + ) + ) { + return this._removeDeprecatedKeys(currentState, 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 + ); + } + + /** + * Removes deprecated keys from storage and returns an + * updated user data object + */ + async _removeDeprecatedKeys(currentState, userData) { + // Bug 1838708: Delete any deprecated high level keys from storage + const keysToRemove = DEPRECATED_DERIVED_KEYS_NAMES.filter(keyName => + userData.hasOwnProperty(keyName) + ); + if (keysToRemove.length) { + const removedKeys = {}; + for (const keyName of keysToRemove) { + removedKeys[keyName] = null; + } + await currentState.updateUserAccountData({ + ...removedKeys, + }); + userData = await currentState.getUserAccountData(); + } + // Bug 1697596 - delete any deprecated scoped keys from storage. + const scopesToRemove = DEPRECATED_KEY_SCOPES.filter(scope => + userData.scopedKeys.hasOwnProperty(scope) + ); + if (scopesToRemove.length) { + const updatedScopedKeys = { + ...userData.scopedKeys, + }; + for (const scope of scopesToRemove) { + delete updatedScopedKeys[scope]; + } + await currentState.updateUserAccountData({ + scopedKeys: updatedScopedKeys, + }); + userData = await currentState.getUserAccountData(); + } + return userData; + } + + /** + * 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 scoped keys are there now + if (!updateData.scopedKeys) { + throw new Error(`user data missing: scopedKeys`); + } + + 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. + 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" + ); + } + 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, + }; + } + + /** + * 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 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().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 { + 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); + } + + _sha256(bytes) { + let hasher = Cc["@mozilla.org/security/hash;1"].createInstance( + Ci.nsICryptoHash + ); + hasher.init(hasher.SHA256); + return CryptoUtils.digestBytes(bytes, hasher); + } +} |