libsignal_protocol_dart
libsignal_protocol_dart is a pure Dart/Flutter implementation of the Signal Protocol.
Documentation
For more information on how the Signal Protocol works:
Usage
Install time
At install time, a signal client needs to generate its identity keys, registration id, and prekeys.
Future<void> install() async {
final identityKeyPair = generateIdentityKeyPair();
final registrationId = generateRegistrationId(false);
final preKeys = generatePreKeys(0, 110);
final signedPreKey = generateSignedPreKey(identityKeyPair, 0);
final sessionStore = InMemorySessionStore();
final preKeyStore = InMemoryPreKeyStore();
final signedPreKeyStore = InMemorySignedPreKeyStore();
final identityStore =
InMemoryIdentityKeyStore(identityKeyPair, registrationId);
for (var p in preKeys) {
await preKeyStore.storePreKey(p.id, p);
}
await signedPreKeyStore.storeSignedPreKey(signedPreKey.id, signedPreKey);
}Building a session
A signal client needs to implement four interfaces: IdentityKeyStore, PreKeyStore, SignedPreKeyStore, and SessionStore. These will manage loading and storing of identity, prekeys, signed prekeys, and session state.
Once those are implemented, you can build a session in this way:
final remoteAddress = SignalProtocolAddress("remote", 1);
final sessionBuilder = SessionBuilder(sessionStore, preKeyStore,
signedPreKeyStore, identityStore, remoteAddress);
sessionBuilder.processPreKeyBundle(retrievedPreKey);
final sessionCipher = SessionCipher(sessionStore, preKeyStore,
signedPreKeyStore, identityStore, remoteAddress);
final ciphertext = sessionCipher.encrypt(utf8.encode("Hello Mixin"));
deliver(ciphertext);Building a group session
If you wanna send message to a group, send a SenderKeyDistributionMessage to all members of the group.
const alice = SignalProtocolAddress('+00000000001', 1);
const groupSender = SenderKeyName('Private group', alice);
final aliceStore = InMemorySenderKeyStore();
final bobStore = InMemorySenderKeyStore();
final aliceSessionBuilder = GroupSessionBuilder(aliceStore);
final bobSessionBuilder = GroupSessionBuilder(bobStore);
final aliceGroupCipher = GroupCipher(aliceStore, groupSender);
final bobGroupCipher = GroupCipher(bobStore, groupSender);
final sentAliceDistributionMessage =
await aliceSessionBuilder.create(groupSender);
final receivedAliceDistributionMessage =
SenderKeyDistributionMessageWrapper.fromSerialized(
sentAliceDistributionMessage.serialize());
await bobSessionBuilder.process(
groupSender, receivedAliceDistributionMessage);
final ciphertextFromAlice = await aliceGroupCipher
.encrypt(Uint8List.fromList(utf8.encode('Hello Mixin')));
final plaintextFromAlice = await bobGroupCipher.decrypt(ciphertextFromAlice);
// ignore: avoid_print
print(utf8.decode(plaintextFromAlice));