1 files changed, 454 insertions, 0 deletions
diff --git a/dom/push/PushCrypto.jsm b/dom/push/PushCrypto.jsm
new file mode 100644
index 000000000..5a669875c
--- /dev/null
+++ b/dom/push/PushCrypto.jsm
@@ -0,0 +1,454 @@
+/* jshint moz: true, esnext: true */
+/* 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 Cu = Components.utils;
+
+Cu.import('resource://gre/modules/Services.jsm');
+Cu.import('resource://gre/modules/XPCOMUtils.jsm');
+
+XPCOMUtils.defineLazyGetter(this, 'gDOMBundle', () =>
+  Services.strings.createBundle('chrome://global/locale/dom/dom.properties'));
+
+Cu.importGlobalProperties(['crypto']);
+
+this.EXPORTED_SYMBOLS = ['PushCrypto', 'concatArray'];
+
+var UTF8 = new TextEncoder('utf-8');
+
+// Legacy encryption scheme (draft-thomson-http-encryption-02).
+var AESGCM128_ENCODING = 'aesgcm128';
+var AESGCM128_ENCRYPT_INFO = UTF8.encode('Content-Encoding: aesgcm128');
+
+// New encryption scheme (draft-ietf-httpbis-encryption-encoding-01).
+var AESGCM_ENCODING = 'aesgcm';
+var AESGCM_ENCRYPT_INFO = UTF8.encode('Content-Encoding: aesgcm');
+
+var NONCE_INFO = UTF8.encode('Content-Encoding: nonce');
+var AUTH_INFO = UTF8.encode('Content-Encoding: auth\0'); // note nul-terminus
+var P256DH_INFO = UTF8.encode('P-256\0');
+var ECDH_KEY = { name: 'ECDH', namedCurve: 'P-256' };
+var ECDSA_KEY =  { name: 'ECDSA', namedCurve: 'P-256' };
+// A default keyid with a name that won't conflict with a real keyid.
+var DEFAULT_KEYID = '';
+
+/** Localized error property names. */
+
+// `Encryption` header missing or malformed.
+const BAD_ENCRYPTION_HEADER = 'PushMessageBadEncryptionHeader';
+// `Crypto-Key` or legacy `Encryption-Key` header missing.
+const BAD_CRYPTO_KEY_HEADER = 'PushMessageBadCryptoKeyHeader';
+const BAD_ENCRYPTION_KEY_HEADER = 'PushMessageBadEncryptionKeyHeader';
+// `Content-Encoding` header missing or contains unsupported encoding.
+const BAD_ENCODING_HEADER = 'PushMessageBadEncodingHeader';
+// `dh` parameter of `Crypto-Key` header missing or not base64url-encoded.
+const BAD_DH_PARAM = 'PushMessageBadSenderKey';
+// `salt` parameter of `Encryption` header missing or not base64url-encoded.
+const BAD_SALT_PARAM = 'PushMessageBadSalt';
+// `rs` parameter of `Encryption` header not a number or less than pad size.
+const BAD_RS_PARAM = 'PushMessageBadRecordSize';
+// Invalid or insufficient padding for encrypted chunk.
+const BAD_PADDING = 'PushMessageBadPaddingError';
+// Generic crypto error.
+const BAD_CRYPTO = 'PushMessageBadCryptoError';
+
+class CryptoError extends Error {
+  /**
+   * Creates an error object indicating an incoming push message could not be
+   * decrypted.
+   *
+   * @param {String} message A human-readable error message. This is only for
+   * internal module logging, and doesn't need to be localized.
+   * @param {String} property The localized property name from `dom.properties`.
+   * @param {String...} params Substitutions to insert into the localized
+   *  string.
+   */
+  constructor(message, property, ...params) {
+    super(message);
+    this.isCryptoError = true;
+    this.property = property;
+    this.params = params;
+  }
+
+  /**
+   * Formats a localized string for reporting decryption errors to the Web
+   * Console.
+   *
+   * @param {String} scope The scope of the service worker receiving the
+   *  message, prepended to any other substitutions in the string.
+   * @returns {String} The localized string.
+   */
+  format(scope) {
+    let params = [scope, ...this.params].map(String);
+    return gDOMBundle.formatStringFromName(this.property, params,
+                                           params.length);
+  }
+}
+
+function getEncryptionKeyParams(encryptKeyField) {
+  if (!encryptKeyField) {
+    return null;
+  }
+  var params = encryptKeyField.split(',');
+  return params.reduce((m, p) => {
+    var pmap = p.split(';').reduce(parseHeaderFieldParams, {});
+    if (pmap.keyid && pmap.dh) {
+      m[pmap.keyid] = pmap.dh;
+    }
+    if (!m[DEFAULT_KEYID] && pmap.dh) {
+      m[DEFAULT_KEYID] = pmap.dh;
+    }
+    return m;
+  }, {});
+}
+
+function getEncryptionParams(encryptField) {
+  if (!encryptField) {
+    throw new CryptoError('Missing encryption header',
+                          BAD_ENCRYPTION_HEADER);
+  }
+  var p = encryptField.split(',', 1)[0];
+  if (!p) {
+    throw new CryptoError('Encryption header missing params',
+                          BAD_ENCRYPTION_HEADER);
+  }
+  return p.split(';').reduce(parseHeaderFieldParams, {});
+}
+
+function getCryptoParams(headers) {
+  if (!headers) {
+    return null;
+  }
+
+  var keymap;
+  var padSize;
+  if (!headers.encoding) {
+    throw new CryptoError('Missing Content-Encoding header',
+                          BAD_ENCODING_HEADER);
+  }
+  if (headers.encoding == AESGCM_ENCODING) {
+    // aesgcm uses the Crypto-Key header, 2 bytes for the pad length, and an
+    // authentication secret.
+    // https://tools.ietf.org/html/draft-ietf-httpbis-encryption-encoding-01
+    keymap = getEncryptionKeyParams(headers.crypto_key);
+    if (!keymap) {
+      throw new CryptoError('Missing Crypto-Key header',
+                            BAD_CRYPTO_KEY_HEADER);
+    }
+    padSize = 2;
+  } else if (headers.encoding == AESGCM128_ENCODING) {
+    // aesgcm128 uses Encryption-Key, 1 byte for the pad length, and no secret.
+    // https://tools.ietf.org/html/draft-thomson-http-encryption-02
+    keymap = getEncryptionKeyParams(headers.encryption_key);
+    if (!keymap) {
+      throw new CryptoError('Missing Encryption-Key header',
+                            BAD_ENCRYPTION_KEY_HEADER);
+    }
+    padSize = 1;
+  } else {
+    throw new CryptoError('Unsupported Content-Encoding: ' + headers.encoding,
+                          BAD_ENCODING_HEADER);
+  }
+
+  var enc = getEncryptionParams(headers.encryption);
+  var dh = keymap[enc.keyid || DEFAULT_KEYID];
+  if (!dh) {
+    throw new CryptoError('Missing dh parameter', BAD_DH_PARAM);
+  }
+  var salt = enc.salt;
+  if (!salt) {
+    throw new CryptoError('Missing salt parameter', BAD_SALT_PARAM);
+  }
+  var rs = enc.rs ? parseInt(enc.rs, 10) : 4096;
+  if (isNaN(rs)) {
+    throw new CryptoError('rs parameter must be a number', BAD_RS_PARAM);
+  }
+  if (rs <= padSize) {
+    throw new CryptoError('rs parameter must be at least ' + padSize,
+                          BAD_RS_PARAM, padSize);
+  }
+  return {dh, salt, rs, padSize};
+}
+
+// Decodes an unpadded, base64url-encoded string.
+function base64URLDecode(string) {
+  try {
+    return ChromeUtils.base64URLDecode(string, {
+      // draft-ietf-httpbis-encryption-encoding-01 prohibits padding.
+      padding: 'reject',
+    });
+  } catch (ex) {}
+  return null;
+}
+
+var parseHeaderFieldParams = (m, v) => {
+  var i = v.indexOf('=');
+  if (i >= 0) {
+    // A quoted string with internal quotes is invalid for all the possible
+    // values of this header field.
+    m[v.substring(0, i).trim()] = v.substring(i + 1).trim()
+                                   .replace(/^"(.*)"$/, '$1');
+  }
+  return m;
+};
+
+function chunkArray(array, size) {
+  var start = array.byteOffset || 0;
+  array = array.buffer || array;
+  var index = 0;
+  var result = [];
+  while(index + size <= array.byteLength) {
+    result.push(new Uint8Array(array, start + index, size));
+    index += size;
+  }
+  if (index < array.byteLength) {
+    result.push(new Uint8Array(array, start + index));
+  }
+  return result;
+}
+
+this.concatArray = function(arrays) {
+  var size = arrays.reduce((total, a) => total + a.byteLength, 0);
+  var index = 0;
+  return arrays.reduce((result, a) => {
+    result.set(new Uint8Array(a), index);
+    index += a.byteLength;
+    return result;
+  }, new Uint8Array(size));
+};
+
+var HMAC_SHA256 = { name: 'HMAC', hash: 'SHA-256' };
+
+function hmac(key) {
+  this.keyPromise = crypto.subtle.importKey('raw', key, HMAC_SHA256,
+                                            false, ['sign']);
+}
+
+hmac.prototype.hash = function(input) {
+  return this.keyPromise.then(k => crypto.subtle.sign('HMAC', k, input));
+};
+
+function hkdf(salt, ikm) {
+  this.prkhPromise = new hmac(salt).hash(ikm)
+    .then(prk => new hmac(prk));
+}
+
+hkdf.prototype.extract = function(info, len) {
+  var input = concatArray([info, new Uint8Array([1])]);
+  return this.prkhPromise
+    .then(prkh => prkh.hash(input))
+    .then(h => {
+      if (h.byteLength < len) {
+        throw new CryptoError('HKDF length is too long', BAD_CRYPTO);
+      }
+      return h.slice(0, len);
+    });
+};
+
+/* generate a 96-bit nonce for use in GCM, 48-bits of which are populated */
+function generateNonce(base, index) {
+  if (index >= Math.pow(2, 48)) {
+    throw new CryptoError('Nonce index is too large', BAD_CRYPTO);
+  }
+  var nonce = base.slice(0, 12);
+  nonce = new Uint8Array(nonce);
+  for (var i = 0; i < 6; ++i) {
+    nonce[nonce.byteLength - 1 - i] ^= (index / Math.pow(256, i)) & 0xff;
+  }
+  return nonce;
+}
+
+this.PushCrypto = {
+
+  generateAuthenticationSecret() {
+    return crypto.getRandomValues(new Uint8Array(16));
+  },
+
+  validateAppServerKey(key) {
+    return crypto.subtle.importKey('raw', key, ECDSA_KEY,
+                                   true, ['verify'])
+      .then(_ => key);
+  },
+
+  generateKeys() {
+    return crypto.subtle.generateKey(ECDH_KEY, true, ['deriveBits'])
+      .then(cryptoKey =>
+         Promise.all([
+           crypto.subtle.exportKey('raw', cryptoKey.publicKey),
+           crypto.subtle.exportKey('jwk', cryptoKey.privateKey)
+         ]));
+  },
+
+  /**
+   * Decrypts a push message.
+   *
+   * @param {JsonWebKey} privateKey The ECDH private key of the subscription
+   *  receiving the message, in JWK form.
+   * @param {BufferSource} publicKey The ECDH public key of the subscription
+   *  receiving the message, in raw form.
+   * @param {BufferSource} authenticationSecret The 16-byte shared
+   *  authentication secret of the subscription receiving the message.
+   * @param {Object} headers The encryption headers passed to `getCryptoParams`.
+   * @param {BufferSource} ciphertext The encrypted message data.
+   * @returns {Promise} Resolves with a `Uint8Array` containing the decrypted
+   *  message data. Rejects with a `CryptoError` if decryption fails.
+   */
+  decrypt(privateKey, publicKey, authenticationSecret, headers, ciphertext) {
+    return Promise.resolve().then(_ => {
+      let cryptoParams = getCryptoParams(headers);
+      if (!cryptoParams) {
+        return null;
+      }
+      return this._decodeMsg(ciphertext, privateKey, publicKey,
+                             cryptoParams.dh, cryptoParams.salt,
+                             cryptoParams.rs, authenticationSecret,
+                             cryptoParams.padSize);
+    }).catch(error => {
+      if (error.isCryptoError) {
+        throw error;
+      }
+      // Web Crypto returns an unhelpful "operation failed for an
+      // operation-specific reason" error if decryption fails. We don't have
+      // context about what went wrong, so we throw a generic error instead.
+      throw new CryptoError('Bad encryption', BAD_CRYPTO);
+    });
+  },
+
+  _decodeMsg(aData, aPrivateKey, aPublicKey, aSenderPublicKey, aSalt, aRs,
+             aAuthenticationSecret, aPadSize) {
+
+    if (aData.byteLength === 0) {
+      // Zero length messages will be passed as null.
+      return null;
+    }
+
+    // The last chunk of data must be less than aRs, if it is not return an
+    // error.
+    if (aData.byteLength % (aRs + 16) === 0) {
+      throw new CryptoError('Encrypted data truncated', BAD_CRYPTO);
+    }
+
+    let senderKey = base64URLDecode(aSenderPublicKey);
+    if (!senderKey) {
+      throw new CryptoError('dh parameter is not base64url-encoded',
+                            BAD_DH_PARAM);
+    }
+
+    let salt = base64URLDecode(aSalt);
+    if (!salt) {
+      throw new CryptoError('salt parameter is not base64url-encoded',
+                            BAD_SALT_PARAM);
+    }
+
+    return Promise.all([
+      crypto.subtle.importKey('raw', senderKey, ECDH_KEY,
+                              false, ['deriveBits']),
+      crypto.subtle.importKey('jwk', aPrivateKey, ECDH_KEY,
+                              false, ['deriveBits'])
+    ])
+    .then(([appServerKey, subscriptionPrivateKey]) =>
+          crypto.subtle.deriveBits({ name: 'ECDH', public: appServerKey },
+                                   subscriptionPrivateKey, 256))
+    .then(ikm => this._deriveKeyAndNonce(aPadSize,
+                                         new Uint8Array(ikm),
+                                         salt,
+                                         aPublicKey,
+                                         senderKey,
+                                         aAuthenticationSecret))
+    .then(r =>
+      // AEAD_AES_128_GCM expands ciphertext to be 16 octets longer.
+      Promise.all(chunkArray(aData, aRs + 16).map((slice, index) =>
+        this._decodeChunk(aPadSize, slice, index, r[1], r[0]))))
+    .then(r => concatArray(r));
+  },
+
+  _deriveKeyAndNonce(padSize, ikm, salt, receiverKey, senderKey,
+                     authenticationSecret) {
+    var kdfPromise;
+    var context;
+    var encryptInfo;
+    // The size of the padding determines which key derivation we use.
+    //
+    // 1. If the pad size is 1, we assume "aesgcm128". This scheme ignores the
+    // authenticationSecret, and uses "Content-Encoding: <blah>" for the
+    // context string. It should eventually be removed: bug 1230038.
+    //
+    // 2. If the pad size is 2, we assume "aesgcm", and mix the
+    // authenticationSecret with the ikm using HKDF. The context string is:
+    // "Content-Encoding: <blah>\0P-256\0" then the length and value of both the
+    // receiver key and sender key.
+    if (padSize == 2) {
+      // Since we are using an authentication secret, we need to run an extra
+      // round of HKDF with the authentication secret as salt.
+      var authKdf = new hkdf(authenticationSecret, ikm);
+      kdfPromise = authKdf.extract(AUTH_INFO, 32)
+        .then(ikm2 => new hkdf(salt, ikm2));
+
+      // aesgcm requires extra context for the info parameter.
+      context = concatArray([
+        new Uint8Array([0]), P256DH_INFO,
+        this._encodeLength(receiverKey), receiverKey,
+        this._encodeLength(senderKey), senderKey
+      ]);
+      encryptInfo = AESGCM_ENCRYPT_INFO;
+    } else {
+      kdfPromise = Promise.resolve(new hkdf(salt, ikm));
+      context = new Uint8Array(0);
+      encryptInfo = AESGCM128_ENCRYPT_INFO;
+    }
+    return kdfPromise.then(kdf => Promise.all([
+      kdf.extract(concatArray([encryptInfo, context]), 16)
+        .then(gcmBits => crypto.subtle.importKey('raw', gcmBits, 'AES-GCM', false,
+                                                 ['decrypt'])),
+      kdf.extract(concatArray([NONCE_INFO, context]), 12)
+    ]));
+  },
+
+  _encodeLength(buffer) {
+    return new Uint8Array([0, buffer.byteLength]);
+  },
+
+  _decodeChunk(aPadSize, aSlice, aIndex, aNonce, aKey) {
+    let params = {
+      name: 'AES-GCM',
+      iv: generateNonce(aNonce, aIndex)
+    };
+    return crypto.subtle.decrypt(params, aKey, aSlice)
+      .then(decoded => this._unpadChunk(aPadSize, new Uint8Array(decoded)));
+  },
+
+  /**
+   * Removes padding from a decrypted chunk.
+   *
+   * @param {Number} padSize The size of the padding length prepended to each
+   *  chunk. For aesgcm, the padding length is expressed as a 16-bit unsigned
+   *  big endian integer. For aesgcm128, the padding is an 8-bit integer.
+   * @param {Uint8Array} decoded The decrypted, padded chunk.
+   * @returns {Uint8Array} The chunk with padding removed.
+   */
+  _unpadChunk(padSize, decoded) {
+    if (padSize < 1 || padSize > 2) {
+      throw new CryptoError('Unsupported pad size', BAD_CRYPTO);
+    }
+    if (decoded.length < padSize) {
+      throw new CryptoError('Decoded array is too short!', BAD_PADDING);
+    }
+    var pad = decoded[0];
+    if (padSize == 2) {
+      pad = (pad << 8) | decoded[1];
+    }
+    if (pad > decoded.length) {
+      throw new CryptoError('Padding is wrong!', BAD_PADDING);
+    }
+    // All padded bytes must be zero except the first one.
+    for (var i = padSize; i <= pad; i++) {
+      if (decoded[i] !== 0) {
+        throw new CryptoError('Padding is wrong!', BAD_PADDING);
+      }
+    }
+    return decoded.slice(pad + padSize);
+  },
+};