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:

• Double Ratchet
• X3DH Key Agreement
• XEdDSA Signature Schemes
• Signal Protocol Java

Usage

Install time

At install time, a signal client needs to generate its identity keys, registration id, and prekeys.

void install() {
  var identityKeyPair = KeyHelper.generateIdentityKeyPair();
  var registerationId = KeyHelper.generateRegistrationId(false);

  var preKeys = KeyHelper.generatePreKeys(0, 110);

  var signedPreKey = KeyHelper.generateSignedPreKey(identityKeyPair, 0);

  var sessionStore = InMemorySessionStore();
  var preKeyStore = InMemoryPreKeyStore();
  var signedPreKeyStore = InMemorySignedPreKeyStore();
  var identityStore =
      InMemoryIdentityKeyStore(identityKeyPair, registerationId);

  for (var p in preKeys) {
    preKeyStore.storePreKey(p.id, p);
  }
  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:

  var remoteAddress = SignalProtocolAddress("remote", 1);
  var sessionBuilder = SessionBuilder(sessionStore, preKeyStore,
      signedPreKeyStore, identityStore, remoteAddress);

  sessionBuilder.processPreKeyBundle(retrievedPreKey);

  var sessionCipher = SessionCipher(sessionStore, preKeyStore,
      signedPreKeyStore, identityStore, remoteAddress);
  var 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.

  var senderKeyName = SenderKeyName("", SignalProtocolAddress("sender", 1));
  var senderKeyStore = InMemorySenderKeyStore();
  var groupSession = GroupCipher(senderKeyStore, senderKeyName);
  groupSession.encrypt(utf8.encode("Hello Mixin"));