Android/src/org/thoughtcrime/securesms/crypto/KeyExchangeProcessor.java

/**
 * Copyright (C) 2011 Whisper Systems
 * Copyright (C) 2013 Open Whisper Systems
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.thoughtcrime.securesms.crypto;

import android.content.Context;
import android.content.Intent;
import android.util.Log;

import org.thoughtcrime.securesms.crypto.protocol.KeyExchangeMessage;
import org.thoughtcrime.securesms.database.DatabaseFactory;
import org.thoughtcrime.securesms.recipients.Recipient;
import org.thoughtcrime.securesms.service.KeyCachingService;
import org.thoughtcrime.securesms.sms.MessageSender;
import org.thoughtcrime.securesms.sms.OutgoingKeyExchangeMessage;
import org.whispersystems.textsecure.crypto.IdentityKey;
import org.whispersystems.textsecure.crypto.InvalidKeyException;
import org.whispersystems.textsecure.crypto.KeyPair;
import org.whispersystems.textsecure.crypto.KeyUtil;
import org.whispersystems.textsecure.crypto.MasterSecret;
import org.whispersystems.textsecure.crypto.PublicKey;
import org.whispersystems.textsecure.crypto.protocol.CiphertextMessage;
import org.whispersystems.textsecure.crypto.protocol.PreKeyBundleMessage;
import org.whispersystems.textsecure.push.PreKeyEntity;
import org.whispersystems.textsecure.storage.InvalidKeyIdException;
import org.whispersystems.textsecure.storage.LocalKeyRecord;
import org.whispersystems.textsecure.storage.PreKeyRecord;
import org.whispersystems.textsecure.storage.RemoteKeyRecord;
import org.whispersystems.textsecure.storage.SessionRecord;
import org.whispersystems.textsecure.util.Conversions;
import org.whispersystems.textsecure.util.Medium;

/**
 * This class processes key exchange interactions.
 *
 * @author Moxie Marlinspike
 */

public class KeyExchangeProcessor {

  public static final String SECURITY_UPDATE_EVENT = "org.thoughtcrime.securesms.KEY_EXCHANGE_UPDATE";

  private Context context;
  private Recipient recipient;
  private MasterSecret masterSecret;
  private LocalKeyRecord localKeyRecord;
  private RemoteKeyRecord remoteKeyRecord;
  private SessionRecord sessionRecord;

  public KeyExchangeProcessor(Context context, MasterSecret masterSecret, Recipient recipient) {
    this.context         = context;
    this.recipient       = recipient;
    this.masterSecret    = masterSecret;

    this.remoteKeyRecord = new RemoteKeyRecord(context, recipient);
    this.localKeyRecord  = new LocalKeyRecord(context, masterSecret, recipient);
    this.sessionRecord   = new SessionRecord(context, masterSecret, recipient);
  }

  public boolean isTrusted(KeyExchangeMessage message) {
    return message.hasIdentityKey() && isTrusted(message.getIdentityKey());
  }

  public boolean isTrusted(PreKeyBundleMessage message) {
    return isTrusted(message.getIdentityKey());
  }

  public boolean isTrusted(IdentityKey identityKey) {
    return DatabaseFactory.getIdentityDatabase(context).isValidIdentity(masterSecret, recipient,
                                                                        identityKey);
  }

  public boolean hasInitiatedSession() {
    return localKeyRecord.getCurrentKeyPair() != null;
  }

  private boolean needsResponseFromUs() {
    return !hasInitiatedSession() || remoteKeyRecord.getCurrentRemoteKey() != null;
  }

  public boolean isStale(KeyExchangeMessage message) {
    int responseKeyId = Conversions.highBitsToMedium(message.getPublicKey().getId());

    Log.w("KeyExchangeProcessor", "Key Exchange High ID Bits: "  + responseKeyId);

    return responseKeyId != 0 &&
      (localKeyRecord.getCurrentKeyPair() != null && localKeyRecord.getCurrentKeyPair().getId() != responseKeyId);
  }

  public void processKeyExchangeMessage(PreKeyBundleMessage message)
      throws InvalidKeyIdException, InvalidKeyException
  {
    int preKeyId               = message.getPreKeyId();
    PublicKey   remoteKey      = message.getPublicKey();
    IdentityKey remoteIdentity = message.getIdentityKey();

    Log.w("KeyExchangeProcessor", "Received pre-key with remote key ID: " + remoteKey.getId());
    Log.w("KeyExchangeProcessor", "Received pre-key with local key ID: " + preKeyId);

    if (!PreKeyRecord.hasRecord(context, preKeyId) && KeyUtil.isSessionFor(context, recipient)) {
      Log.w("KeyExchangeProcessor", "We've already processed the prekey part, letting bundled message fall through...");
      return;
    }

    if (!PreKeyRecord.hasRecord(context, preKeyId))
      throw new InvalidKeyIdException("No such prekey: " + preKeyId);

    PreKeyRecord preKeyRecord = new PreKeyRecord(context, masterSecret, preKeyId);
    KeyPair      preKeyPair   = new KeyPair(preKeyId, preKeyRecord.getKeyPair().getKeyPair(), masterSecret);

    localKeyRecord.setCurrentKeyPair(preKeyPair);
    localKeyRecord.setNextKeyPair(preKeyPair);

    remoteKeyRecord.setCurrentRemoteKey(remoteKey);
    remoteKeyRecord.setLastRemoteKey(remoteKey);

    sessionRecord.setSessionId(localKeyRecord.getCurrentKeyPair().getPublicKey().getFingerprintBytes(),
                               remoteKeyRecord.getCurrentRemoteKey().getFingerprintBytes());
    sessionRecord.setIdentityKey(remoteIdentity);
    sessionRecord.setSessionVersion(Math.min(message.getSupportedVersion(), PreKeyBundleMessage.SUPPORTED_VERSION));
    sessionRecord.setNegotiatedSessionVersion(sessionRecord.getSessionVersion());

    localKeyRecord.save();
    remoteKeyRecord.save();
    sessionRecord.save();

    if (preKeyId != Medium.MAX_VALUE) {
      PreKeyRecord.delete(context, preKeyId);
    }

    DatabaseFactory.getIdentityDatabase(context)
                   .saveIdentity(masterSecret, recipient, remoteIdentity);
  }

  public void processKeyExchangeMessage(PreKeyEntity message) {
    PublicKey remoteKey = new PublicKey(message.getKeyId(), message.getPublicKey());
    remoteKeyRecord.setCurrentRemoteKey(remoteKey);
    remoteKeyRecord.setLastRemoteKey(remoteKey);
    remoteKeyRecord.save();

    localKeyRecord = KeyUtil.initializeRecordFor(context, masterSecret, recipient, CiphertextMessage.SUPPORTED_VERSION);
    localKeyRecord.setNextKeyPair(localKeyRecord.getCurrentKeyPair());
    localKeyRecord.save();

    sessionRecord.setSessionId(localKeyRecord.getCurrentKeyPair().getPublicKey().getFingerprintBytes(),
                               remoteKeyRecord.getCurrentRemoteKey().getFingerprintBytes());
    sessionRecord.setIdentityKey(message.getIdentityKey());
    sessionRecord.setNegotiatedSessionVersion(CiphertextMessage.SUPPORTED_VERSION);
    sessionRecord.setSessionVersion(CiphertextMessage.SUPPORTED_VERSION);
    sessionRecord.setPrekeyBundleRequired(true);
    sessionRecord.save();

    DatabaseFactory.getIdentityDatabase(context)
                   .saveIdentity(masterSecret, recipient, message.getIdentityKey());
  }

  public void processKeyExchangeMessage(KeyExchangeMessage message, long threadId) {
    int initiateKeyId = Conversions.lowBitsToMedium(message.getPublicKey().getId());
    message.getPublicKey().setId(initiateKeyId);

    if (needsResponseFromUs()) {
      localKeyRecord                = KeyUtil.initializeRecordFor(context, masterSecret, recipient, message.getMessageVersion());
      KeyExchangeMessage ourMessage = new KeyExchangeMessage(context, masterSecret, Math.min(CiphertextMessage.SUPPORTED_VERSION, message.getMaxVersion()), localKeyRecord, initiateKeyId);
      OutgoingKeyExchangeMessage textMessage = new OutgoingKeyExchangeMessage(recipient, ourMessage.serialize());
      Log.w("KeyExchangeProcessor", "Responding with key exchange message fingerprint: " + ourMessage.getPublicKey().getFingerprint());
      Log.w("KeyExchangeProcessor", "Which has a local key record fingerprint: " + localKeyRecord.getCurrentKeyPair().getPublicKey().getFingerprint());
      MessageSender.send(context, masterSecret, textMessage, threadId);
    }

    remoteKeyRecord.setCurrentRemoteKey(message.getPublicKey());
    remoteKeyRecord.setLastRemoteKey(message.getPublicKey());
    remoteKeyRecord.save();

    sessionRecord.setSessionId(localKeyRecord.getCurrentKeyPair().getPublicKey().getFingerprintBytes(),
                               remoteKeyRecord.getCurrentRemoteKey().getFingerprintBytes());
    sessionRecord.setIdentityKey(message.getIdentityKey());
    sessionRecord.setSessionVersion(Math.min(CiphertextMessage.SUPPORTED_VERSION, message.getMaxVersion()));
    sessionRecord.setNegotiatedSessionVersion(sessionRecord.getSessionVersion());

    Log.w("KeyExchangeUtil", "Setting session version: " + Math.min(CiphertextMessage.SUPPORTED_VERSION, message.getMaxVersion()));

    sessionRecord.save();

    if (message.hasIdentityKey()) {
      DatabaseFactory.getIdentityDatabase(context)
                     .saveIdentity(masterSecret, recipient, message.getIdentityKey());
    }

    DecryptingQueue.scheduleRogueMessages(context, masterSecret, recipient);

    Intent intent = new Intent(SECURITY_UPDATE_EVENT);
    intent.putExtra("thread_id", threadId);
    intent.setPackage(context.getPackageName());
    context.sendBroadcast(intent, KeyCachingService.KEY_PERMISSION);
  }

}