Using The Java Library

Getting the library

For Java projects:

<dependency>
  <groupId>org.whispersystems</groupId>
  <artifactId>libsignal-service-java</artifactId>
  <version>(latest version here)</version>
</dependency>

For Android projects:

compile 'org.whispersystems:libsignal-service-android:(latest version here)'

Implementing the Signal Protocol interfaces

Signal Protocol is a stateful protocol, so libsignal-service users
need to implement the storage interface SignalProtocolStore, which handles load/store
of your key and session information to durable media.

Creating keys

IdentityKeyPair    identityKey        = KeyHelper.generateIdentityKeyPair();
List<PreKeyRecord> oneTimePreKeys     = KeyHelper.generatePreKeys(100);
PreKeyRecord       lastResortKey      = KeyHelper.generateLastResortKey();
SignedPreKeyRecord signedPreKeyRecord = KeyHelper.generateSignedPreKey(identityKey, signedPreKeyId);

The above keys are then stored locally so that they're available for load via the SignalProtocolStore.

Registering

At install time, clients need to register with the Signal server.

private final String     URL         = "https://my.signal.server.com";
private final TrustStore TRUST_STORE = new MyTrustStoreImpl();
private final String     USERNAME    = "+14151231234";
private final String     PASSWORD    = generateRandomPassword();

SignalServiceAccountManager accountManager = new SignalServiceAccountManager(URL, TRUST_STORE,USERNAME, PASSWORD);

accountManager.requestSmsVerificationCode();
accountManager.verifyAccount(receivedSmsVerificationCode, generateRandomSignalingKey(), false, generateRandomInstallId());
accountManager.setGcmId(Optional.of(GoogleCloudMessaging.getInstance(this).register(REGISTRATION_ID)));
accountManager.setPreKeys(identityKey.getPublic(), lastResortKey, signedPreKey, oneTimePreKeys);

Sending text messages

SignalServiceMessageSender messageSender = new SignalServiceMessageSender(URL, TRUST_STORE, USERNAME, PASSWORD,
                                                                    localRecipientId, new MySignalProtocolStore(),
                                                                    Optional.absent());

messageSender.sendMessage(new SignalServiceAddress("+14159998888"),
                          SignalServiceDataMessage.newBuilder()
                                                  .withBody("Hello, world!")
                                                  .build());

Sending media messages

SignalServiceMessageSender messageSender = new SignalServiceMessageSender(URL, TRUST_STORE, USERNAME, PASSWORD,
                                                                    localRecipientId, new MySignalProtocolStore(),
                                                                    Optional.absent());

File                 myAttachment     = new File("/path/to/my.attachment");
FileInputStream      attachmentStream = new FileInputStream(myAttachment);
SignalServiceAttachment attachment    = SignalServiceAttachment.newStreamBuilder()
                                                            .withStream(attachmentStream)
                                                            .withContentType("image/png")
                                                            .withLength(myAttachment.size())
                                                            .build();

messageSender.sendMessage(new SignalServiceAddress("+14159998888"),
                          SignalServiceDataMessage.newBuilder()
                                                  .withBody("An attachment!")
                                                  .withAttachment(attachment)
                                                  .build());

Receiving messages

SignalServiceMessageReceiver messageReceiver = new SignalServiceMessageReceiver(URL, TRUST_STORE, USERNAME, PASSWORD, mySignalingKey);
SignalServiceMessagePipe     messagePipe;

try {
  messagePipe = messageReciever.createMessagePipe();

  while (listeningForMessages) {
    SignalServiceEnvelope envelope     = messagePipe.read(timeout, timeoutTimeUnit);
    SignalServiceCipher   cipher       = new SignalServiceCipher(new MySignalProtocolStore());
    SignalServiceDataMessage message   = cipher.decrypt(envelope);

    System.out.println("Received message: " + message.getBody().get());
  }

} finally {
  if (messagePipe != null)
    messagePipe.close();
}

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