signal-desktop/js/crypto.js

// functions exposed for replacement and direct calling in test code
var crypto_tests = {};

window.crypto = (function() {
	function getRandomBytes(size) {
		//TODO: Better random (https://www.grc.com/r&d/js.htm?)
		try {
			var buffer = new ArrayBuffer(size);
			var array = new Uint8Array(buffer);
			window.crypto.getRandomValues(array);
			return buffer;
		} catch (err) {
			//TODO: ummm...wat?
			throw err;
		}
	}

	function HmacSHA256(key, input) {
		return window.crypto.subtle.sign({name: "HMAC", hash: "SHA-256"}, key, input);
	}


	crypto_tests.privToPub = function(privKey, isIdentity) {
		if (privKey.byteLength != 32)
			throw new Error("Invalid private key");

		var prependVersion = function(pubKey) {
			var origPub = new Uint8Array(pubKey);
			var pub = new ArrayBuffer(33);
			var pubWithPrefix = new Uint8Array(pub);
			for (var i = 0; i < 32; i++)
				pubWithPrefix[i+1] = origPub[i];
			pubWithPrefix[0] = 5;
			return pub;
		}

		if (USE_NACL) {
			return postNaclMessage({command: "bytesToPriv", priv: privKey}).then(function(message) {
				var priv = message.res;
				if (!isIdentity)
					new Uint8Array(priv)[0] |= 0x01;
				return postNaclMessage({command: "privToPub", priv: priv}).then(function(message) {
					return { pubKey: prependVersion(message.res), privKey: priv };
				});
			});
		} else {
			privKey = privKey.slice(0);
			var priv = new Uint16Array(privKey);
			priv[0] &= 0xFFF8;
			priv[15] = (priv[15] & 0x7FFF) | 0x4000;

			if (!isIdentity)
				priv[0] |= 0x0001;

			//TODO: fscking type conversion
			return new Promise.resolve({ pubKey: prependVersion(toArrayBuffer(curve25519(priv))), privKey: privKey});
		}
	
	}
	var privToPub = function(privKey, isIdentity) { return crypto_tests.privToPub(privKey, isIdentity); }

	crypto_tests.createNewKeyPair = function(isIdentity) {
		return privToPub(getRandomBytes(32), isIdentity);
	}
	var createNewKeyPair = function(isIdentity) { return crypto_tests.createNewKeyPair(isIdentity); }

	var crypto_storage = {};

	crypto_storage.getNewPubKeySTORINGPrivKey = function(keyName, isIdentity) {
		return createNewKeyPair(isIdentity).then(function(keyPair) {
			storage.putEncrypted("25519Key" + keyName, keyPair);
			return keyPair.pubKey;
		});
	}

	crypto_storage.getStoredPubKey = function(keyName) {
		return toArrayBuffer(storage.getEncrypted("25519Key" + keyName, { pubKey: undefined }).pubKey);
	}

	crypto_storage.getStoredKeyPair = function(keyName) {
		var res = storage.getEncrypted("25519Key" + keyName);
		if (res === undefined)
			return undefined;
		return { pubKey: toArrayBuffer(res.pubKey), privKey: toArrayBuffer(res.privKey) };
	}

	crypto_storage.getAndRemoveStoredKeyPair = function(keyName) {
		var keyPair = this.getStoredKeyPair(keyName);
		storage.removeEncrypted("25519Key" + keyName);
		return keyPair;
	}

	crypto_storage.getAndRemovePreKeyPair = function(keyId) {
		return this.getAndRemoveStoredKeyPair("preKey" + keyId);
	}

	crypto_storage.getIdentityPrivKey = function() {
		return this.getStoredKeyPair("identityKey").privKey;
	}

	crypto_storage.saveSession = function(encodedNumber, session) {
		storage.putEncrypted("session" + getEncodedNumber(encodedNumber), session);
	}

	crypto_storage.getSession = function(encodedNumber) {
		return storage.getEncrypted("session" + getEncodedNumber(encodedNumber));
	}


	/*****************************
	 *** Internal Crypto stuff ***
	 *****************************/
	//TODO: Think about replacing CryptoJS stuff with optional NaCL-based implementations
	// Probably means all of the low-level crypto stuff here needs pulled out into its own file
	crypto_tests.ECDHE = function(pubKey, privKey) {
		if (privKey !== undefined) {
			privKey = toArrayBuffer(privKey);
			if (privKey.byteLength != 32)
				throw new Error("Invalid private key");
		} else
			throw new Error("Invalid private key");

		if (pubKey !== undefined) {
			pubKey = toArrayBuffer(pubKey);
			var pubView = new Uint8Array(pubKey);
			if (pubKey.byteLength == 33 && pubView[0] == 5) {
				pubKey = new ArrayBuffer(32);
				var pubCopy = new Uint8Array(pubKey);
				for (var i = 0; i < 32; i++)
					pubCopy[i] = pubView[i+1];
			} else if (pubKey.byteLength != 32)
				throw new Error("Invalid public key");
		}

		return new Promise(function(resolve) {
			if (USE_NACL) {
				postNaclMessage({command: "ECDHE", priv: privKey, pub: pubKey}).then(function(message) {
					resolve(message.res);
				});
			} else {
				resolve(toArrayBuffer(curve25519(new Uint16Array(privKey), new Uint16Array(pubKey))));
			}
		});
	}
	var ECDHE = function(pubKey, privKey) { return crypto_tests.ECDHE(pubKey, privKey); }

	crypto_tests.HKDF = function(input, salt, info) {
		// Specific implementation of RFC 5869 that only returns exactly 64 bytes
		return HmacSHA256(salt, toArrayBuffer(input)).then(function(PRK) {
			var infoString = getString(info);
			// TextSecure implements a slightly tweaked version of RFC 5869: the 0 and 1 should be 1 and 2 here
			return HmacSHA256(PRK, toArrayBuffer(infoString + String.fromCharCode(0))).then(function(T1) {
				return HmacSHA256(PRK, toArrayBuffer(getString(T1) + infoString + String.fromCharCode(1))).then(function(T2) {
					return [ T1, T2 ];
				});
			});
		});
	}

	var HKDF = function(input, salt, info) {
		// HKDF for TextSecure has a bit of additional handling - salts always end up being 32 bytes
		if (salt == '') {
			salt = new ArrayBuffer(32);
			var uintKey = new Uint8Array(salt);
			for (var i = 0; i < 32; i++)
				uintKey[i] = 0;
		}

		salt = toArrayBuffer(salt);

		if (salt.byteLength != 32)
			throw new Error("Got salt of incorrect length");

		return crypto_tests.HKDF(input, salt, info);
	}

	var verifyMACWithVersionByte = function(data, key, mac, version) {
		if (version === undefined)
			version = 1;

		return HmacSHA256(key, toArrayBuffer(String.fromCharCode(version) + getString(data))).then(function(calculated_mac) {
			var macString = getString(mac);

			if (calculated_mac.substring(0, macString.length) != macString)
				throw new Error("Bad MAC");
		});
	}

	var calculateMACWithVersionByte = function(data, key, version) {
		if (version === undefined)
			version = 1;

		return HmacSHA256(key, toArrayBuffer(String.fromCharCode(version) + getString(data)));
	}

	/******************************
	 *** Ratchet implementation ***
	 ******************************/
	var calculateRatchet = function(session, remoteKey, sending) {
		var ratchet = session.currentRatchet;

		return ECDHE(remoteKey, ratchet.ephemeralKeyPair.privKey).then(function(sharedSecret) {
			return HKDF(sharedSecret, ratchet.rootKey, "WhisperRatchet").then(function(masterKey) {
				if (sending)
					session[getString(ratchet.ephemeralKeyPair.pubKey)]	= { messageKeys: {}, chainKey: { counter: -1, key: masterKey[1] } };
				else
					session[getString(remoteKey)]						= { messageKeys: {}, chainKey: { counter: -1, key: masterKey[1] } };
				ratchet.rootKey = masterKey[0];
			});
		});
	}

	var initSession = function(isInitiator, ourEphemeralKey, encodedNumber, theirIdentityPubKey, theirEphemeralPubKey) {
		var ourIdentityPrivKey = crypto_storage.getIdentityPrivKey();

		var sharedSecret;
		return ECDHE(theirEphemeralPubKey, ourIdentityPrivKey).then(function(ecRes) {
			sharedSecret = getString(ecRes);

			function finishInit() {
				return ECDHE(theirEphemeralPubKey, ourEphemeralKey.privKey).then(function(ecRes) {
					sharedSecret += getString(ecRes);

					return HKDF(toArrayBuffer(sharedSecret), '', "WhisperText").then(function(masterKey) {
						var session = {currentRatchet: { rootKey: masterKey[0], lastRemoteEphemeralKey: theirEphemeralPubKey },
										oldRatchetList: []
									};

						// If we're initiating we go ahead and set our first sending ephemeral key now,
						// otherwise we figure it out when we first maybeStepRatchet with the remote's ephemeral key
						if (isInitiator) {
							return createNewKeyPair(false).then(function(ourSendingEphemeralKey) {
								session.currentRatchet.ephemeralKeyPair = ourSendingEphemeralKey;
								return calculateRatchet(session, theirEphemeralPubKey, true).then(function() {
									crypto_storage.saveSession(encodedNumber, session);
								});
							});
						} else {
							session.currentRatchet.ephemeralKeyPair = ourEphemeralKey;
							crypto_storage.saveSession(encodedNumber, session);
						}
					});
				});
			}

			if (isInitiator)
				return ECDHE(theirIdentityPubKey, ourEphemeralKey.privKey).then(function(ecRes) {
					sharedSecret = sharedSecret + getString(ecRes);
				}).then(finishInit);
			else
				return ECDHE(theirIdentityPubKey, ourEphemeralKey.privKey).then(function(ecRes) {
					sharedSecret = getString(ecRes) + sharedSecret;
				}).then(finishInit);
		});
	}

	var initSessionFromPreKeyWhisperMessage = function(encodedNumber, message) {
		//TODO: Check remote identity key matches known-good key

		var preKeyPair = crypto_storage.getAndRemovePreKeyPair(message.preKeyId);
		if (preKeyPair === undefined) {
			if (crypto_storage.getSession(encodedNumber) !== undefined)
				return new Promise(function(resolve) { resolve() });
			else
				throw new Error("Missing preKey for PreKeyWhisperMessage");
		} else
			return initSession(false, preKeyPair, encodedNumber, message.identityKey, message.baseKey);
	}

	var fillMessageKeys = function(chain, counter) {
		if (chain.chainKey.counter + 1000 < counter) //TODO: maybe 1000 is too low/high in some cases?
			return new Promise(function(resolve) { resolve() }); // Stalker, much?

		if (chain.chainKey.counter < counter) {
			var key = toArrayBuffer(chain.chainKey.key);
			return HmacSHA256(key, toArrayBuffer(String.fromCharCode(1))).then(function(mac) {
				return HmacSHA256(key, toArrayBuffer(String.fromCharCode(2))).then(function(key) {
					chain.messageKeys[chain.chainKey.counter + 1] = mac;
					chain.chainKey.key = key
					chain.chainKey.counter += 1;
					return fillMessageKeys(chain, counter);
				});
			});
		} else
			return new Promise(function(resolve) { resolve() });
	}

	var maybeStepRatchet = function(session, remoteKey, previousCounter) {
		if (session[getString(remoteKey)] !== undefined)
			return new Promise(function(resolve) { resolve() });

		var ratchet = session.currentRatchet;

		var finish = function() {
			return calculateRatchet(session, remoteKey, false).then(function() {
				// Now swap the ephemeral key and calculate the new sending chain
				var previousRatchet = getString(ratchet.ephemeralKeyPair.pubKey);
				if (session[previousRatchet] !== undefined) {
					ratchet.previousCounter = session[previousRatchet].chainKey.counter;
					delete session[getString(ratchet.ephemeralKeyPair.pubKey)];
				} else
					// TODO: This is just an idiosyncrasy upstream, which we match for testing
					// it should be changed upstream to something more reasonable.
					ratchet.previousCounter = 4294967295;

				return createNewKeyPair(false).then(function(keyPair) {
					ratchet.ephemeralKeyPair = keyPair;
					return calculateRatchet(session, remoteKey, true).then(function() {
						ratchet.lastRemoteEphemeralKey = remoteKey;
					});
				});
			});
		}

		var previousRatchet = session[getString(ratchet.lastRemoteEphemeralKey)];
		if (previousRatchet !== undefined) {
			return fillMessageKeys(previousRatchet, previousCounter).then(function() {
				if (!objectContainsKeys(previousRatchet.messageKeys))
					delete session[getString(ratchet.lastRemoteEphemeralKey)];
				else
					session.oldRatchetList[session.oldRatchetList.length] = { added: new Date().getTime(), ephemeralKey: ratchet.lastRemoteEphemeralKey };
			}).then(finish);
		} else
			return finish();
	}

	// returns decrypted protobuf
	var decryptWhisperMessage = function(encodedNumber, messageBytes) {
		var session = crypto_storage.getSession(encodedNumber);
		if (session === undefined)
			throw new Error("No session currently open with " + encodedNumber);

		if (messageBytes[0] != String.fromCharCode((2 << 4) | 2))
			throw new Error("Bad version number on WhisperMessage");

		var messageProto = messageBytes.substring(1, messageBytes.length - 8);
		var mac = messageBytes.substring(messageBytes.length - 8, messageBytes.length);

		var message = decodeWhisperMessageProtobuf(messageProto);

		return maybeStepRatchet(session, message.ephemeralKey, message.previousCounter).then(function() {
			var chain = session[getString(message.ephemeralKey)];

			return fillMessageKeys(chain, message.counter).then(function() {
				return HKDF(chain.messageKeys[message.counter], '', "WhisperMessageKeys").then(function(keys) {
					delete chain.messageKeys[message.counter];

					verifyMACWithVersionByte(messageProto, keys[1], mac, (2 << 4) | 2);
					var counter = intToArrayBuffer(message.counter);
					return window.crypto.subtle.decrypt({name: "AES-CTR", counter: counter}, keys[0], toArrayBuffer(message.ciphertext))
												.then(function(plaintext) {

						//TODO: removeOldChains(session);
						delete session['pendingPreKey'];

						crypto_storage.saveSession(encodedNumber, session);
						return decodePushMessageContentProtobuf(getString(plaintext));
					});
				});
			});
		});
	}

	/*************************
	 *** Public crypto API ***
	 *************************/
	// Decrypts message into a raw string
	crypto.decryptWebsocketMessage = function(message) {
		var signaling_key = storage.getEncrypted("signaling_key"); //TODO: in crypto_storage
		var aes_key = signaling_key.substring(0, 32);
		var mac_key = signaling_key.substring(32, 32 + 20);

		var decodedMessage = new Uint8Array(base64DecToArr(getString(message)));
		if (decodedMessage[0] != 1)
			throw new Error("Got bad version number: " + decodedMessage[0]);

		var iv = decodedMessage.subarray(1, 1 + 16);
		var ciphertext = decodedMessage.subarray(1 + 16, decodedMessage.length - 10);
		var ivAndCipherText = decodedMessage.subarray(1, decodedMessage.length - 10);
		var mac = decodedMessage.subarray(decodedMessage.length - 10, decodedMessage.length);

		return verifyMACWithVersionByte(ivAndCipherText, mac_key, mac).then(function() {
			return window.crypto.subtle.decrypt({name: "AES-CBC", iv: iv}, aes_key, ciphertext);
		});
	};

	crypto.handleIncomingPushMessageProto = function(proto) {
		switch(proto.type) {
		case 0: //TYPE_MESSAGE_PLAINTEXT
			return Promise.resolve({message: decodePushMessageContentProtobuf(getString(proto.message)), pushMessage:proto});
		case 1: //TYPE_MESSAGE_CIPHERTEXT
			return decryptWhisperMessage(proto.source, getString(proto.message)).then(function(result) {
				return {message: result, pushMessage: proto};
			});
		case 3: //TYPE_MESSAGE_PREKEY_BUNDLE
			if (proto.message.readUint8() != (2 << 4 | 2))
				throw new Error("Bad version byte");
			var preKeyProto = decodePreKeyWhisperMessageProtobuf(getString(proto.message));
			return initSessionFromPreKeyWhisperMessage(proto.source, preKeyProto).then(function() {
				return decryptWhisperMessage(proto.source, getString(preKeyProto.message)).then(function(result) {
					return {message: result, pushMessage: proto};
				});
			});
		}
	}

	// return Promise(encoded [PreKey]WhisperMessage)
	crypto.encryptMessageFor = function(deviceObject, pushMessageContent) {
		var session = crypto_storage.getSession(deviceObject.encodedNumber);

		var doEncryptPushMessageContent = function() {
			var msg = new WhisperMessageProtobuf();
			var plaintext = toArrayBuffer(pushMessageContent.encode());

			msg.ephemeralKey = toArrayBuffer(session.currentRatchet.ephemeralKeyPair.pubKey);
			var chain = session[getString(msg.ephemeralKey)];

			return fillMessageKeys(chain, chain.chainKey.counter + 1).then(function() {
				return HKDF(chain.messageKeys[chain.chainKey.counter], '', "WhisperMessageKeys").then(function(keys) {
					delete chain.messageKeys[chain.chainKey.counter];
					msg.counter = chain.chainKey.counter;
					msg.previousCounter = session.currentRatchet.previousCounter;

					var counter = intToArrayBuffer(chain.chainKey.counter);
					return window.crypto.subtle.encrypt({name: "AES-CTR", counter: counter}, keys[0], plaintext).then(function(ciphertext) {
						msg.ciphertext = ciphertext;
						var encodedMsg = getString(msg.encode());

						return calculateMACWithVersionByte(encodedMsg, keys[1], (2 << 4) | 2).then(function(mac) {
							var result = String.fromCharCode((2 << 4) | 2) + encodedMsg + getString(mac).substring(0, 8);
							crypto_storage.saveSession(deviceObject.encodedNumber, session);
							return result;
						});
					});
				});
			});
		}

		var preKeyMsg = new PreKeyWhisperMessageProtobuf();
		preKeyMsg.identityKey = toArrayBuffer(crypto_storage.getStoredPubKey("identityKey"));
		preKeyMsg.preKeyId = deviceObject.preKeyId;
		preKeyMsg.registrationId = deviceObject.registrationId;

		if (session === undefined) {
			return createNewKeyPair(false).then(function(baseKey) {
				preKeyMsg.baseKey = toArrayBuffer(baseKey.pubKey);
				return initSession(true, baseKey, deviceObject.encodedNumber, deviceObject.identityKey, deviceObject.publicKey).then(function() {
					//TODO: Delete preKey info on first message received back
					session = crypto_storage.getSession(deviceObject.encodedNumber);
					session.pendingPreKey = baseKey.pubKey;
					return doEncryptPushMessageContent().then(function(message) {
						preKeyMsg.message = toArrayBuffer(message);
						var result = String.fromCharCode((2 << 4) | 2) + getString(preKeyMsg.encode());
						return {type: 3, body: result};
					});
				});
			});
		} else
			return doEncryptPushMessageContent().then(function(message) {
				if (session.pendingPreKey !== undefined) {
					preKeyMsg.baseKey = toArrayBuffer(session.pendingPreKey);
					preKeyMsg.message = toArrayBuffer(message);
					var result = String.fromCharCode((2 << 4) | 2) + getString(preKeyMsg.encode());
					return {type: 3, body: result};
				} else
					return {type: 1, body: getString(message)};
			});
	}

	var GENERATE_KEYS_KEYS_GENERATED = 100;
	crypto.generateKeys = function() {
		var identityKey = crypto_storage.getStoredPubKey("identityKey");
		var identityKeyCalculated = function(pubKey) {
			identityKey = pubKey;

			var firstKeyId = storage.getEncrypted("maxPreKeyId", -1) + 1;
			storage.putEncrypted("maxPreKeyId", firstKeyId + GENERATE_KEYS_KEYS_GENERATED);

			if (firstKeyId > 16777000)
				return new Promise(function() { throw new Error("You crazy motherfucker") });

			var keys = {};
			keys.keys = [];
			var keysLeft = GENERATE_KEYS_KEYS_GENERATED;
			return new Promise(function(resolve) {
				for (var i = firstKeyId; i < firstKeyId + GENERATE_KEYS_KEYS_GENERATED; i++) {
					crypto_storage.getNewPubKeySTORINGPrivKey("preKey" + i, false).then(function(pubKey) {
						keys.keys[i] = {keyId: i, publicKey: pubKey, identityKey: identityKey};
						keysLeft--;
						if (keysLeft == 0) {
							// 0xFFFFFF == 16777215
							keys.lastResortKey = {keyId: 16777215, publicKey: crypto_storage.getStoredPubKey("preKey16777215"), identityKey: identityKey};//TODO: Rotate lastResortKey
							if (keys.lastResortKey.publicKey === undefined) {
								return crypto_storage.getNewPubKeySTORINGPrivKey("preKey16777215", false).then(function(pubKey) {
									keys.lastResortKey.publicKey = pubKey;
									resolve(keys);
								});
							} else
								resolve(keys);
						}
					});
				}
			});
		}
		if (identityKey === undefined)
			return crypto_storage.getNewPubKeySTORINGPrivKey("identityKey", true).then(function(pubKey) { return identityKeyCalculated(pubKey); });
		else
			return identityKeyCalculated(identityKey);
	}
})();