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Signal Protocol cryptography library for Java
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//
// Copyright 2014-2016 Signal Messenger, LLC.
// SPDX-License-Identifier: AGPL-3.0-only
//

package org.signal.libsignal.protocol.state;

import org.signal.libsignal.internal.CalledFromNative;
import org.signal.libsignal.protocol.IdentityKey;
import org.signal.libsignal.protocol.IdentityKeyPair;
import org.signal.libsignal.protocol.SignalProtocolAddress;

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

  @CalledFromNative
  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);
}