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Signal Protocol cryptography library for Java

There is a newer version: 2.8.1

/**
 * Copyright (C) 2014-2016 Open Whisper Systems
 *
 * Licensed according to the LICENSE file in this repository.
 */
package org.whispersystems.libsignal.state;

import org.whispersystems.libsignal.IdentityKey;
import org.whispersystems.libsignal.IdentityKeyPair;
import org.whispersystems.libsignal.SignalProtocolAddress;

/**
 * Provides an interface to identity information.
 *
 * @author Moxie Marlinspike
 */
public interface IdentityKeyStore {

  public enum Direction {
    SENDING, RECEIVING
  }

  /**
   * Get the local client's identity key pair.
   *
   * @return The local client's persistent identity key pair.
   */
  public IdentityKeyPair getIdentityKeyPair();

  /**
   * Return the local client's registration ID.
   * 
   * Clients should maintain a registration ID, a random number
   * between 1 and 16380 that's generated once at install time.
   *
   * @return the local client's registration ID.
   */
  public int             getLocalRegistrationId();

  /**
   * Save a remote client's identity key
   * 

   * Store a remote client's identity key as trusted.
   *
   * @param address     The address of the remote client.
   * @param identityKey The remote client's identity key.
   * @return True if the identity key replaces a previous identity, false if not
   */
  public boolean         saveIdentity(SignalProtocolAddress address, IdentityKey identityKey);


  /**
   * Verify a remote client's identity key.
   * 
   * Determine whether a remote client's identity is trusted.  Convention is
   * that the Signal Protocol is 'trust on first use.'  This means that
   * an identity key is considered 'trusted' if there is no entry for the recipient
   * in the local store, or if it matches the saved key for a recipient in the local
   * store.  Only if it mismatches an entry in the local store is it considered
   * 'untrusted.'
   *
   * Clients may wish to make a distinction as to how keys are trusted based on the
   * direction of travel. For instance, clients may wish to accept all 'incoming' identity
   * key changes, while only blocking identity key changes when sending a message.
   *
   * @param address     The address of the remote client.
   * @param identityKey The identity key to verify.
   * @param direction   The direction (sending or receiving) this identity is being used for.
   * @return true if trusted, false if untrusted.
   */
  public boolean         isTrustedIdentity(SignalProtocolAddress address, IdentityKey identityKey, Direction direction);


  /**
   * Return the saved public identity key for a remote client
   *
   * @param address The address of the remote client
   * @return The public identity key, or null if absent
   */
  public IdentityKey getIdentity(SignalProtocolAddress address);

}