The axolotl encryption protocol is a stateful protocol, so libtextsecure users need to implement the storage interface AxolotlStore, 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 are then stored locally so that they're available for load via the AxolotlStore.

Registering

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

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

TextSecureAccountManager accountManager = new TextSecureAccountManager(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

TextSecureMessageSender messageSender = new TextSecureMessageSender(URL, TRUST_STORE, USERNAME, PASSWORD,
                                                                    localRecipientId, new MyAxolotlStore(),
                                                                    Optional.absent());

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

Sending media messages

TextSecureMessageSender messageSender = new TextSecureMessageSender(URL, TRUST_STORE, USERNAME, PASSWORD,
                                                                    localRecipientId, new MyAxolotlStore(),
                                                                    Optional.absent());

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

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

Receiving messages

TextSecureMessageReceiver messageReceiver = new TextSecureMessageReceiver(URL, TRUST_STORE, USERNAME, PASSWORD, mySignalingKey);
TextSecureMessagePipe     messagePipe;

try {
  messagePipe = messageReciever.createMessagePipe();

  while (listeningForMessages) {
    TextSecureEnvelope envelope = messagePipe.read(timeout, timeoutTimeUnit);
    TextSecureCipher   cipher   = new TextSecureCipher(new MyAxolotlStore());
    TextSecureMessage message   = cipher.decrypt(envelope);

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

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