예제 #1
0
  /**
   * Handles a specific <tt>IOException</tt> which was thrown during the execution of {@link
   * #runInConnectThread(DTLSProtocol, TlsPeer, DatagramTransport)} while trying to establish a DTLS
   * connection
   *
   * @param ioe the <tt>IOException</tt> to handle
   * @param msg the human-readable message to log about the specified <tt>ioe</tt>
   * @param i the number of tries remaining after the current one
   * @return <tt>true</tt> if the specified <tt>ioe</tt> was successfully handled; <tt>false</tt>,
   *     otherwise
   */
  private boolean handleRunInConnectThreadException(IOException ioe, String msg, int i) {
    // SrtpControl.start(MediaType) starts its associated TransformEngine.
    // We will use that mediaType to signal the normal stop then as well
    // i.e. we will ignore exception after the procedure to stop this
    // PacketTransformer has begun.
    if (mediaType == null) return false;

    if (ioe instanceof TlsFatalAlert) {
      TlsFatalAlert tfa = (TlsFatalAlert) ioe;
      short alertDescription = tfa.getAlertDescription();

      if (alertDescription == AlertDescription.unexpected_message) {
        msg += " Received fatal unexpected message.";
        if (i == 0
            || !Thread.currentThread().equals(connectThread)
            || connector == null
            || mediaType == null) {
          msg += " Giving up after " + (CONNECT_TRIES - i) + " retries.";
        } else {
          msg += " Will retry.";
          logger.error(msg, ioe);

          return true;
        }
      } else {
        msg += " Received fatal alert " + alertDescription + ".";
      }
    }

    logger.error(msg, ioe);
    return false;
  }
예제 #2
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 /** Stops this <tt>PacketTransformer</tt>. */
 private synchronized void stop() {
   if (connectThread != null) connectThread = null;
   try {
     // The dtlsTransport and _srtpTransformer SHOULD be closed, of
     // course. The datagramTransport MUST be closed.
     if (dtlsTransport != null) {
       try {
         dtlsTransport.close();
       } catch (IOException ioe) {
         logger.error("Failed to (properly) close " + dtlsTransport.getClass(), ioe);
       }
       dtlsTransport = null;
     }
     if (_srtpTransformer != null) {
       _srtpTransformer.close();
       _srtpTransformer = null;
     }
   } finally {
     try {
       closeDatagramTransport();
     } finally {
       notifyAll();
     }
   }
 }
예제 #3
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 /**
  * Closes {@link #datagramTransport} if it is non-<tt>null</tt> and logs and swallows any
  * <tt>IOException</tt>.
  */
 private void closeDatagramTransport() {
   if (datagramTransport != null) {
     try {
       datagramTransport.close();
     } catch (IOException ioe) {
       // DatagramTransportImpl has no reason to fail because it is
       // merely an adapter of #connector and this PacketTransformer to
       // the terms of the Bouncy Castle Crypto API.
       logger.error("Failed to (properly) close " + datagramTransport.getClass(), ioe);
     }
     datagramTransport = null;
   }
 }
예제 #4
0
  /**
   * Sends the data contained in a specific byte array as application data through the DTLS
   * connection of this <tt>DtlsPacketTransformer</tt>.
   *
   * @param buf the byte array containing data to send.
   * @param off the offset in <tt>buf</tt> where the data begins.
   * @param len the length of data to send.
   */
  public void sendApplicationData(byte[] buf, int off, int len) {
    DTLSTransport dtlsTransport = this.dtlsTransport;
    Throwable throwable = null;

    if (dtlsTransport != null) {
      try {
        dtlsTransport.send(buf, off, len);
      } catch (IOException ioe) {
        throwable = ioe;
      }
    } else {
      throwable = new NullPointerException("dtlsTransport");
    }
    if (throwable != null) {
      // SrtpControl.start(MediaType) starts its associated
      // TransformEngine. We will use that mediaType to signal the normal
      // stop then as well i.e. we will ignore exception after the
      // procedure to stop this PacketTransformer has begun.
      if (mediaType != null && !tlsPeerHasRaisedCloseNotifyWarning) {
        logger.error("Failed to send application data over DTLS transport: ", throwable);
      }
    }
  }
예제 #5
0
  /** Starts this <tt>PacketTransformer</tt>. */
  private synchronized void start() {
    if (this.datagramTransport != null) {
      if (this.connectThread == null && dtlsTransport == null) {
        logger.warn(
            getClass().getName()
                + " has been started but has failed to establish"
                + " the DTLS connection!");
      }
      return;
    }

    if (rtcpmux && Component.RTCP == componentID) {
      // In the case of rtcp-mux, the RTCP transformer does not create
      // a DTLS session. The SRTP context (_srtpTransformer) will be
      // initialized on demand using initializeSRTCPTransformerFromRtp().
      return;
    }

    AbstractRTPConnector connector = this.connector;

    if (connector == null) throw new NullPointerException("connector");

    DtlsControl.Setup setup = this.setup;
    SecureRandom secureRandom = DtlsControlImpl.createSecureRandom();
    final DTLSProtocol dtlsProtocolObj;
    final TlsPeer tlsPeer;

    if (DtlsControl.Setup.ACTIVE.equals(setup)) {
      dtlsProtocolObj = new DTLSClientProtocol(secureRandom);
      tlsPeer = new TlsClientImpl(this);
    } else {
      dtlsProtocolObj = new DTLSServerProtocol(secureRandom);
      tlsPeer = new TlsServerImpl(this);
    }
    tlsPeerHasRaisedCloseNotifyWarning = false;

    final DatagramTransportImpl datagramTransport = new DatagramTransportImpl(componentID);

    datagramTransport.setConnector(connector);

    Thread connectThread =
        new Thread() {
          @Override
          public void run() {
            try {
              runInConnectThread(dtlsProtocolObj, tlsPeer, datagramTransport);
            } finally {
              if (Thread.currentThread().equals(DtlsPacketTransformer.this.connectThread)) {
                DtlsPacketTransformer.this.connectThread = null;
              }
            }
          }
        };

    connectThread.setDaemon(true);
    connectThread.setName(DtlsPacketTransformer.class.getName() + ".connectThread");

    this.connectThread = connectThread;
    this.datagramTransport = datagramTransport;

    boolean started = false;

    try {
      connectThread.start();
      started = true;
    } finally {
      if (!started) {
        if (connectThread.equals(this.connectThread)) this.connectThread = null;
        if (datagramTransport.equals(this.datagramTransport)) this.datagramTransport = null;
      }
    }

    notifyAll();
  }
예제 #6
0
  /** {@inheritDoc} */
  @Override
  public RawPacket reverseTransform(RawPacket pkt) {
    byte[] buf = pkt.getBuffer();
    int off = pkt.getOffset();
    int len = pkt.getLength();

    if (isDtlsRecord(buf, off, len)) {
      if (rtcpmux && Component.RTCP == componentID) {
        // This should never happen.
        logger.warn(
            "Dropping a DTLS record, because it was received on the"
                + " RTCP channel while rtcpmux is in use.");
        return null;
      }

      boolean receive;

      synchronized (this) {
        if (datagramTransport == null) {
          receive = false;
        } else {
          datagramTransport.queueReceive(buf, off, len);
          receive = true;
        }
      }
      if (receive) {
        DTLSTransport dtlsTransport = this.dtlsTransport;

        if (dtlsTransport == null) {
          // The specified pkt looks like a DTLS record and it has
          // been consumed for the purposes of the secure channel
          // represented by this PacketTransformer.
          pkt = null;
        } else {
          try {
            int receiveLimit = dtlsTransport.getReceiveLimit();
            int delta = receiveLimit - len;

            if (delta > 0) {
              pkt.grow(delta);
              buf = pkt.getBuffer();
              off = pkt.getOffset();
              len = pkt.getLength();
            } else if (delta < 0) {
              pkt.shrink(-delta);
              buf = pkt.getBuffer();
              off = pkt.getOffset();
              len = pkt.getLength();
            }

            int received = dtlsTransport.receive(buf, off, len, DTLS_TRANSPORT_RECEIVE_WAITMILLIS);

            if (received <= 0) {
              // No application data was decoded.
              pkt = null;
            } else {
              delta = len - received;
              if (delta > 0) pkt.shrink(delta);
            }
          } catch (IOException ioe) {
            pkt = null;
            // SrtpControl.start(MediaType) starts its associated
            // TransformEngine. We will use that mediaType to signal
            // the normal stop then as well i.e. we will ignore
            // exception after the procedure to stop this
            // PacketTransformer has begun.
            if (mediaType != null && !tlsPeerHasRaisedCloseNotifyWarning) {
              logger.error("Failed to decode a DTLS record!", ioe);
            }
          }
        }
      } else {
        // The specified pkt looks like a DTLS record but it is
        // unexpected in the current state of the secure channel
        // represented by this PacketTransformer. This PacketTransformer
        // has not been started (successfully) or has been closed.
        pkt = null;
      }
    } else if (transformEngine.isSrtpDisabled()) {
      // In pure DTLS mode only DTLS records pass through.
      pkt = null;
    } else {
      // DTLS-SRTP has not been initialized yet or has failed to
      // initialize.
      SinglePacketTransformer srtpTransformer = waitInitializeAndGetSRTPTransformer();

      if (srtpTransformer != null) pkt = srtpTransformer.reverseTransform(pkt);
      else if (DROP_UNENCRYPTED_PKTS) pkt = null;
      // XXX Else, it is our explicit policy to let the received packet
      // pass through and rely on the SrtpListener to notify the user that
      // the session is not secured.
    }
    return pkt;
  }
예제 #7
0
/**
 * Implements {@link PacketTransformer} for DTLS-SRTP. It's capable of working in pure DTLS mode if
 * appropriate flag was set in <tt>DtlsControlImpl</tt>.
 *
 * @author Lyubomir Marinov
 */
public class DtlsPacketTransformer extends SinglePacketTransformer {
  private static final long CONNECT_RETRY_INTERVAL = 500;

  /**
   * The maximum number of times that {@link #runInConnectThread(DTLSProtocol, TlsPeer,
   * DatagramTransport)} is to retry the invocations of {@link DTLSClientProtocol#connect(TlsClient,
   * DatagramTransport)} and {@link DTLSServerProtocol#accept(TlsServer, DatagramTransport)} in
   * anticipation of a successful connection.
   */
  private static final int CONNECT_TRIES = 3;

  /**
   * The indicator which determines whether unencrypted packets sent or received through
   * <tt>DtlsPacketTransformer</tt> are to be dropped. The default value is <tt>false</tt>.
   *
   * @see #DROP_UNENCRYPTED_PKTS_PNAME
   */
  private static final boolean DROP_UNENCRYPTED_PKTS;

  /**
   * The name of the <tt>ConfigurationService</tt> and/or <tt>System</tt> property which indicates
   * whether unencrypted packets sent or received through <tt>DtlsPacketTransformer</tt> are to be
   * dropped. The default value is <tt>false</tt>.
   */
  private static final String DROP_UNENCRYPTED_PKTS_PNAME =
      DtlsPacketTransformer.class.getName() + ".dropUnencryptedPkts";

  /** The length of the header of a DTLS record. */
  static final int DTLS_RECORD_HEADER_LENGTH = 13;

  /**
   * The number of milliseconds a <tt>DtlsPacketTransform</tt> is to wait on its {@link
   * #dtlsTransport} in order to receive a packet.
   */
  private static final int DTLS_TRANSPORT_RECEIVE_WAITMILLIS = -1;

  /**
   * The <tt>Logger</tt> used by the <tt>DtlsPacketTransformer</tt> class and its instances to print
   * debug information.
   */
  private static final Logger logger = Logger.getLogger(DtlsPacketTransformer.class);

  static {
    ConfigurationService cfg = LibJitsi.getConfigurationService();
    boolean dropUnencryptedPkts = false;

    if (cfg == null) {
      String s = System.getProperty(DROP_UNENCRYPTED_PKTS_PNAME);

      if (s != null) dropUnencryptedPkts = Boolean.parseBoolean(s);
    } else {
      dropUnencryptedPkts = cfg.getBoolean(DROP_UNENCRYPTED_PKTS_PNAME, dropUnencryptedPkts);
    }
    DROP_UNENCRYPTED_PKTS = dropUnencryptedPkts;
  }

  /**
   * Determines whether a specific array of <tt>byte</tt>s appears to contain a DTLS record.
   *
   * @param buf the array of <tt>byte</tt>s to be analyzed
   * @param off the offset within <tt>buf</tt> at which the analysis is to start
   * @param len the number of bytes within <tt>buf</tt> starting at <tt>off</tt> to be analyzed
   * @return <tt>true</tt> if the specified <tt>buf</tt> appears to contain a DTLS record
   */
  public static boolean isDtlsRecord(byte[] buf, int off, int len) {
    boolean b = false;

    if (len >= DTLS_RECORD_HEADER_LENGTH) {
      short type = TlsUtils.readUint8(buf, off);

      switch (type) {
        case ContentType.alert:
        case ContentType.application_data:
        case ContentType.change_cipher_spec:
        case ContentType.handshake:
          int major = buf[off + 1] & 0xff;
          int minor = buf[off + 2] & 0xff;
          ProtocolVersion version = null;

          if ((major == ProtocolVersion.DTLSv10.getMajorVersion())
              && (minor == ProtocolVersion.DTLSv10.getMinorVersion())) {
            version = ProtocolVersion.DTLSv10;
          }
          if ((version == null)
              && (major == ProtocolVersion.DTLSv12.getMajorVersion())
              && (minor == ProtocolVersion.DTLSv12.getMinorVersion())) {
            version = ProtocolVersion.DTLSv12;
          }
          if (version != null) {
            int length = TlsUtils.readUint16(buf, off + 11);

            if (DTLS_RECORD_HEADER_LENGTH + length <= len) b = true;
          }
          break;
        default:
          // Unless a new ContentType has been defined by the Bouncy
          // Castle Crypto APIs, the specified buf does not represent a
          // DTLS record.
          break;
      }
    }
    return b;
  }

  /** The ID of the component which this instance works for/is associated with. */
  private final int componentID;

  /** The <tt>RTPConnector</tt> which uses this <tt>PacketTransformer</tt>. */
  private AbstractRTPConnector connector;

  /** The background <tt>Thread</tt> which initializes {@link #dtlsTransport}. */
  private Thread connectThread;

  /**
   * The <tt>DatagramTransport</tt> implementation which adapts {@link #connector} and this
   * <tt>PacketTransformer</tt> to the terms of the Bouncy Castle Crypto APIs.
   */
  private DatagramTransportImpl datagramTransport;

  /**
   * The <tt>DTLSTransport</tt> through which the actual packet transformations are being performed
   * by this instance.
   */
  private DTLSTransport dtlsTransport;

  /** The <tt>MediaType</tt> of the stream which this instance works for/is associated with. */
  private MediaType mediaType;

  /**
   * Whether rtcp-mux is in use.
   *
   * <p>If enabled, and this is the transformer for RTCP, it will not establish a DTLS session on
   * its own, but rather wait for the RTP transformer to do so, and reuse it to initialize the SRTP
   * transformer.
   */
  private boolean rtcpmux = false;

  /**
   * The value of the <tt>setup</tt> SDP attribute defined by RFC 4145 &quot;TCP-Based Media
   * Transport in the Session Description Protocol (SDP)&quot; which determines whether this
   * instance acts as a DTLS client or a DTLS server.
   */
  private DtlsControl.Setup setup;

  /** The {@code SRTPTransformer} (to be) used by this instance. */
  private SinglePacketTransformer _srtpTransformer;

  /**
   * The indicator which determines whether the <tt>TlsPeer</tt> employed by this
   * <tt>PacketTransformer</tt> has raised an <tt>AlertDescription.close_notify</tt>
   * <tt>AlertLevel.warning</tt> i.e. the remote DTLS peer has closed the write side of the
   * connection.
   */
  private boolean tlsPeerHasRaisedCloseNotifyWarning;

  /** The <tt>TransformEngine</tt> which has initialized this instance. */
  private final DtlsTransformEngine transformEngine;

  /**
   * Initializes a new <tt>DtlsPacketTransformer</tt> instance.
   *
   * @param transformEngine the <tt>TransformEngine</tt> which is initializing the new instance
   * @param componentID the ID of the component for which the new instance is to work
   */
  public DtlsPacketTransformer(DtlsTransformEngine transformEngine, int componentID) {
    this.transformEngine = transformEngine;
    this.componentID = componentID;
  }

  /** {@inheritDoc} */
  @Override
  public synchronized void close() {
    // SrtpControl.start(MediaType) starts its associated TransformEngine.
    // We will use that mediaType to signal the normal stop then as well
    // i.e. we will call setMediaType(null) first.
    setMediaType(null);
    setConnector(null);
  }

  /**
   * Closes {@link #datagramTransport} if it is non-<tt>null</tt> and logs and swallows any
   * <tt>IOException</tt>.
   */
  private void closeDatagramTransport() {
    if (datagramTransport != null) {
      try {
        datagramTransport.close();
      } catch (IOException ioe) {
        // DatagramTransportImpl has no reason to fail because it is
        // merely an adapter of #connector and this PacketTransformer to
        // the terms of the Bouncy Castle Crypto API.
        logger.error("Failed to (properly) close " + datagramTransport.getClass(), ioe);
      }
      datagramTransport = null;
    }
  }

  /**
   * Determines whether {@link #runInConnectThread(DTLSProtocol, TlsPeer, DatagramTransport)} is to
   * try to establish a DTLS connection.
   *
   * @param i the number of tries remaining after the current one
   * @param datagramTransport
   * @return <tt>true</tt> to try to establish a DTLS connection; otherwise, <tt>false</tt>
   */
  private boolean enterRunInConnectThreadLoop(int i, DatagramTransport datagramTransport) {
    if (i < 0 || i > CONNECT_TRIES) {
      return false;
    } else {
      Thread currentThread = Thread.currentThread();

      synchronized (this) {
        if (i > 0 && i < CONNECT_TRIES - 1) {
          boolean interrupted = false;

          try {
            wait(CONNECT_RETRY_INTERVAL);
          } catch (InterruptedException ie) {
            interrupted = true;
          }
          if (interrupted) currentThread.interrupt();
        }

        return currentThread.equals(this.connectThread)
            && datagramTransport.equals(this.datagramTransport);
      }
    }
  }

  /**
   * Gets the <tt>DtlsControl</tt> implementation associated with this instance.
   *
   * @return the <tt>DtlsControl</tt> implementation associated with this instance
   */
  DtlsControlImpl getDtlsControl() {
    return getTransformEngine().getDtlsControl();
  }

  /**
   * Gets the <tt>TransformEngine</tt> which has initialized this instance.
   *
   * @return the <tt>TransformEngine</tt> which has initialized this instance
   */
  DtlsTransformEngine getTransformEngine() {
    return transformEngine;
  }

  /**
   * Handles a specific <tt>IOException</tt> which was thrown during the execution of {@link
   * #runInConnectThread(DTLSProtocol, TlsPeer, DatagramTransport)} while trying to establish a DTLS
   * connection
   *
   * @param ioe the <tt>IOException</tt> to handle
   * @param msg the human-readable message to log about the specified <tt>ioe</tt>
   * @param i the number of tries remaining after the current one
   * @return <tt>true</tt> if the specified <tt>ioe</tt> was successfully handled; <tt>false</tt>,
   *     otherwise
   */
  private boolean handleRunInConnectThreadException(IOException ioe, String msg, int i) {
    // SrtpControl.start(MediaType) starts its associated TransformEngine.
    // We will use that mediaType to signal the normal stop then as well
    // i.e. we will ignore exception after the procedure to stop this
    // PacketTransformer has begun.
    if (mediaType == null) return false;

    if (ioe instanceof TlsFatalAlert) {
      TlsFatalAlert tfa = (TlsFatalAlert) ioe;
      short alertDescription = tfa.getAlertDescription();

      if (alertDescription == AlertDescription.unexpected_message) {
        msg += " Received fatal unexpected message.";
        if (i == 0
            || !Thread.currentThread().equals(connectThread)
            || connector == null
            || mediaType == null) {
          msg += " Giving up after " + (CONNECT_TRIES - i) + " retries.";
        } else {
          msg += " Will retry.";
          logger.error(msg, ioe);

          return true;
        }
      } else {
        msg += " Received fatal alert " + alertDescription + ".";
      }
    }

    logger.error(msg, ioe);
    return false;
  }

  /**
   * Tries to initialize {@link #_srtpTransformer} by using the <tt>DtlsPacketTransformer</tt> for
   * RTP.
   *
   * @return the (possibly updated) value of {@link #_srtpTransformer}.
   */
  private SinglePacketTransformer initializeSRTCPTransformerFromRtp() {
    DtlsPacketTransformer rtpTransformer =
        (DtlsPacketTransformer) getTransformEngine().getRTPTransformer();

    // Prevent recursion (that is pretty much impossible to ever happen).
    if (rtpTransformer != this) {
      PacketTransformer srtpTransformer = rtpTransformer.waitInitializeAndGetSRTPTransformer();

      if (srtpTransformer != null && srtpTransformer instanceof SRTPTransformer) {
        synchronized (this) {
          if (_srtpTransformer == null) {
            _srtpTransformer = new SRTCPTransformer((SRTPTransformer) srtpTransformer);
            // For the sake of completeness, we notify whenever we
            // assign to _srtpTransformer.
            notifyAll();
          }
        }
      }
    }

    return _srtpTransformer;
  }

  /**
   * Initializes a new <tt>SRTPTransformer</tt> instance with a specific (negotiated)
   * <tt>SRTPProtectionProfile</tt> and the keying material specified by a specific
   * <tt>TlsContext</tt>.
   *
   * @param srtpProtectionProfile the (negotiated) <tt>SRTPProtectionProfile</tt> to initialize the
   *     new instance with
   * @param tlsContext the <tt>TlsContext</tt> which represents the keying material
   * @return a new <tt>SRTPTransformer</tt> instance initialized with <tt>srtpProtectionProfile</tt>
   *     and <tt>tlsContext</tt>
   */
  private SinglePacketTransformer initializeSRTPTransformer(
      int srtpProtectionProfile, TlsContext tlsContext) {
    boolean rtcp;

    switch (componentID) {
      case Component.RTCP:
        rtcp = true;
        break;
      case Component.RTP:
        rtcp = false;
        break;
      default:
        throw new IllegalStateException("componentID");
    }

    int cipher_key_length;
    int cipher_salt_length;
    int cipher;
    int auth_function;
    int auth_key_length;
    int RTCP_auth_tag_length, RTP_auth_tag_length;

    switch (srtpProtectionProfile) {
      case SRTPProtectionProfile.SRTP_AES128_CM_HMAC_SHA1_32:
        cipher_key_length = 128 / 8;
        cipher_salt_length = 112 / 8;
        cipher = SRTPPolicy.AESCM_ENCRYPTION;
        auth_function = SRTPPolicy.HMACSHA1_AUTHENTICATION;
        auth_key_length = 160 / 8;
        RTCP_auth_tag_length = 80 / 8;
        RTP_auth_tag_length = 32 / 8;
        break;
      case SRTPProtectionProfile.SRTP_AES128_CM_HMAC_SHA1_80:
        cipher_key_length = 128 / 8;
        cipher_salt_length = 112 / 8;
        cipher = SRTPPolicy.AESCM_ENCRYPTION;
        auth_function = SRTPPolicy.HMACSHA1_AUTHENTICATION;
        auth_key_length = 160 / 8;
        RTCP_auth_tag_length = RTP_auth_tag_length = 80 / 8;
        break;
      case SRTPProtectionProfile.SRTP_NULL_HMAC_SHA1_32:
        cipher_key_length = 0;
        cipher_salt_length = 0;
        cipher = SRTPPolicy.NULL_ENCRYPTION;
        auth_function = SRTPPolicy.HMACSHA1_AUTHENTICATION;
        auth_key_length = 160 / 8;
        RTCP_auth_tag_length = 80 / 8;
        RTP_auth_tag_length = 32 / 8;
        break;
      case SRTPProtectionProfile.SRTP_NULL_HMAC_SHA1_80:
        cipher_key_length = 0;
        cipher_salt_length = 0;
        cipher = SRTPPolicy.NULL_ENCRYPTION;
        auth_function = SRTPPolicy.HMACSHA1_AUTHENTICATION;
        auth_key_length = 160 / 8;
        RTCP_auth_tag_length = RTP_auth_tag_length = 80 / 8;
        break;
      default:
        throw new IllegalArgumentException("srtpProtectionProfile");
    }

    byte[] keyingMaterial =
        tlsContext.exportKeyingMaterial(
            ExporterLabel.dtls_srtp, null, 2 * (cipher_key_length + cipher_salt_length));
    byte[] client_write_SRTP_master_key = new byte[cipher_key_length];
    byte[] server_write_SRTP_master_key = new byte[cipher_key_length];
    byte[] client_write_SRTP_master_salt = new byte[cipher_salt_length];
    byte[] server_write_SRTP_master_salt = new byte[cipher_salt_length];
    byte[][] keyingMaterialValues = {
      client_write_SRTP_master_key,
      server_write_SRTP_master_key,
      client_write_SRTP_master_salt,
      server_write_SRTP_master_salt
    };

    for (int i = 0, keyingMaterialOffset = 0; i < keyingMaterialValues.length; i++) {
      byte[] keyingMaterialValue = keyingMaterialValues[i];

      System.arraycopy(
          keyingMaterial, keyingMaterialOffset, keyingMaterialValue, 0, keyingMaterialValue.length);
      keyingMaterialOffset += keyingMaterialValue.length;
    }

    SRTPPolicy srtcpPolicy =
        new SRTPPolicy(
            cipher,
            cipher_key_length,
            auth_function,
            auth_key_length,
            RTCP_auth_tag_length,
            cipher_salt_length);
    SRTPPolicy srtpPolicy =
        new SRTPPolicy(
            cipher,
            cipher_key_length,
            auth_function,
            auth_key_length,
            RTP_auth_tag_length,
            cipher_salt_length);
    SRTPContextFactory clientSRTPContextFactory =
        new SRTPContextFactory(
            /* sender */ tlsContext instanceof TlsClientContext,
            client_write_SRTP_master_key,
            client_write_SRTP_master_salt,
            srtpPolicy,
            srtcpPolicy);
    SRTPContextFactory serverSRTPContextFactory =
        new SRTPContextFactory(
            /* sender */ tlsContext instanceof TlsServerContext,
            server_write_SRTP_master_key,
            server_write_SRTP_master_salt,
            srtpPolicy,
            srtcpPolicy);
    SRTPContextFactory forwardSRTPContextFactory;
    SRTPContextFactory reverseSRTPContextFactory;

    if (tlsContext instanceof TlsClientContext) {
      forwardSRTPContextFactory = clientSRTPContextFactory;
      reverseSRTPContextFactory = serverSRTPContextFactory;
    } else if (tlsContext instanceof TlsServerContext) {
      forwardSRTPContextFactory = serverSRTPContextFactory;
      reverseSRTPContextFactory = clientSRTPContextFactory;
    } else {
      throw new IllegalArgumentException("tlsContext");
    }

    SinglePacketTransformer srtpTransformer;

    if (rtcp) {
      srtpTransformer = new SRTCPTransformer(forwardSRTPContextFactory, reverseSRTPContextFactory);
    } else {
      srtpTransformer = new SRTPTransformer(forwardSRTPContextFactory, reverseSRTPContextFactory);
    }
    return srtpTransformer;
  }

  /**
   * Notifies this instance that the DTLS record layer associated with a specific <tt>TlsPeer</tt>
   * has raised an alert.
   *
   * @param tlsPeer the <tt>TlsPeer</tt> whose associated DTLS record layer has raised an alert
   * @param alertLevel {@link AlertLevel}
   * @param alertDescription {@link AlertDescription}
   * @param message a human-readable message explaining what caused the alert. May be <tt>null</tt>.
   * @param cause the exception that caused the alert to be raised. May be <tt>null</tt>.
   */
  void notifyAlertRaised(
      TlsPeer tlsPeer, short alertLevel, short alertDescription, String message, Exception cause) {
    if (AlertLevel.warning == alertLevel && AlertDescription.close_notify == alertDescription) {
      tlsPeerHasRaisedCloseNotifyWarning = true;
    }
  }

  /** {@inheritDoc} */
  @Override
  public RawPacket reverseTransform(RawPacket pkt) {
    byte[] buf = pkt.getBuffer();
    int off = pkt.getOffset();
    int len = pkt.getLength();

    if (isDtlsRecord(buf, off, len)) {
      if (rtcpmux && Component.RTCP == componentID) {
        // This should never happen.
        logger.warn(
            "Dropping a DTLS record, because it was received on the"
                + " RTCP channel while rtcpmux is in use.");
        return null;
      }

      boolean receive;

      synchronized (this) {
        if (datagramTransport == null) {
          receive = false;
        } else {
          datagramTransport.queueReceive(buf, off, len);
          receive = true;
        }
      }
      if (receive) {
        DTLSTransport dtlsTransport = this.dtlsTransport;

        if (dtlsTransport == null) {
          // The specified pkt looks like a DTLS record and it has
          // been consumed for the purposes of the secure channel
          // represented by this PacketTransformer.
          pkt = null;
        } else {
          try {
            int receiveLimit = dtlsTransport.getReceiveLimit();
            int delta = receiveLimit - len;

            if (delta > 0) {
              pkt.grow(delta);
              buf = pkt.getBuffer();
              off = pkt.getOffset();
              len = pkt.getLength();
            } else if (delta < 0) {
              pkt.shrink(-delta);
              buf = pkt.getBuffer();
              off = pkt.getOffset();
              len = pkt.getLength();
            }

            int received = dtlsTransport.receive(buf, off, len, DTLS_TRANSPORT_RECEIVE_WAITMILLIS);

            if (received <= 0) {
              // No application data was decoded.
              pkt = null;
            } else {
              delta = len - received;
              if (delta > 0) pkt.shrink(delta);
            }
          } catch (IOException ioe) {
            pkt = null;
            // SrtpControl.start(MediaType) starts its associated
            // TransformEngine. We will use that mediaType to signal
            // the normal stop then as well i.e. we will ignore
            // exception after the procedure to stop this
            // PacketTransformer has begun.
            if (mediaType != null && !tlsPeerHasRaisedCloseNotifyWarning) {
              logger.error("Failed to decode a DTLS record!", ioe);
            }
          }
        }
      } else {
        // The specified pkt looks like a DTLS record but it is
        // unexpected in the current state of the secure channel
        // represented by this PacketTransformer. This PacketTransformer
        // has not been started (successfully) or has been closed.
        pkt = null;
      }
    } else if (transformEngine.isSrtpDisabled()) {
      // In pure DTLS mode only DTLS records pass through.
      pkt = null;
    } else {
      // DTLS-SRTP has not been initialized yet or has failed to
      // initialize.
      SinglePacketTransformer srtpTransformer = waitInitializeAndGetSRTPTransformer();

      if (srtpTransformer != null) pkt = srtpTransformer.reverseTransform(pkt);
      else if (DROP_UNENCRYPTED_PKTS) pkt = null;
      // XXX Else, it is our explicit policy to let the received packet
      // pass through and rely on the SrtpListener to notify the user that
      // the session is not secured.
    }
    return pkt;
  }

  /**
   * Runs in {@link #connectThread} to initialize {@link #dtlsTransport}.
   *
   * @param dtlsProtocol
   * @param tlsPeer
   * @param datagramTransport
   */
  private void runInConnectThread(
      DTLSProtocol dtlsProtocol, TlsPeer tlsPeer, DatagramTransport datagramTransport) {
    DTLSTransport dtlsTransport = null;
    final boolean srtp = !transformEngine.isSrtpDisabled();
    int srtpProtectionProfile = 0;
    TlsContext tlsContext = null;

    // DTLS client
    if (dtlsProtocol instanceof DTLSClientProtocol) {
      DTLSClientProtocol dtlsClientProtocol = (DTLSClientProtocol) dtlsProtocol;
      TlsClientImpl tlsClient = (TlsClientImpl) tlsPeer;

      for (int i = CONNECT_TRIES - 1; i >= 0; i--) {
        if (!enterRunInConnectThreadLoop(i, datagramTransport)) break;
        try {
          dtlsTransport = dtlsClientProtocol.connect(tlsClient, datagramTransport);
          break;
        } catch (IOException ioe) {
          if (!handleRunInConnectThreadException(
              ioe, "Failed to connect this DTLS client to a DTLS" + " server!", i)) {
            break;
          }
        }
      }
      if (dtlsTransport != null && srtp) {
        srtpProtectionProfile = tlsClient.getChosenProtectionProfile();
        tlsContext = tlsClient.getContext();
      }
    }
    // DTLS server
    else if (dtlsProtocol instanceof DTLSServerProtocol) {
      DTLSServerProtocol dtlsServerProtocol = (DTLSServerProtocol) dtlsProtocol;
      TlsServerImpl tlsServer = (TlsServerImpl) tlsPeer;

      for (int i = CONNECT_TRIES - 1; i >= 0; i--) {
        if (!enterRunInConnectThreadLoop(i, datagramTransport)) break;
        try {
          dtlsTransport = dtlsServerProtocol.accept(tlsServer, datagramTransport);
          break;
        } catch (IOException ioe) {
          if (!handleRunInConnectThreadException(
              ioe, "Failed to accept a connection from a DTLS client!", i)) {
            break;
          }
        }
      }
      if (dtlsTransport != null && srtp) {
        srtpProtectionProfile = tlsServer.getChosenProtectionProfile();
        tlsContext = tlsServer.getContext();
      }
    } else {
      // It MUST be either a DTLS client or a DTLS server.
      throw new IllegalStateException("dtlsProtocol");
    }

    SinglePacketTransformer srtpTransformer =
        (dtlsTransport == null || !srtp)
            ? null
            : initializeSRTPTransformer(srtpProtectionProfile, tlsContext);
    boolean closeSRTPTransformer;

    synchronized (this) {
      if (Thread.currentThread().equals(this.connectThread)
          && datagramTransport.equals(this.datagramTransport)) {
        this.dtlsTransport = dtlsTransport;
        _srtpTransformer = srtpTransformer;
        notifyAll();
      }
      closeSRTPTransformer = (_srtpTransformer != srtpTransformer);
    }
    if (closeSRTPTransformer && srtpTransformer != null) srtpTransformer.close();
  }

  /**
   * Sends the data contained in a specific byte array as application data through the DTLS
   * connection of this <tt>DtlsPacketTransformer</tt>.
   *
   * @param buf the byte array containing data to send.
   * @param off the offset in <tt>buf</tt> where the data begins.
   * @param len the length of data to send.
   */
  public void sendApplicationData(byte[] buf, int off, int len) {
    DTLSTransport dtlsTransport = this.dtlsTransport;
    Throwable throwable = null;

    if (dtlsTransport != null) {
      try {
        dtlsTransport.send(buf, off, len);
      } catch (IOException ioe) {
        throwable = ioe;
      }
    } else {
      throwable = new NullPointerException("dtlsTransport");
    }
    if (throwable != null) {
      // SrtpControl.start(MediaType) starts its associated
      // TransformEngine. We will use that mediaType to signal the normal
      // stop then as well i.e. we will ignore exception after the
      // procedure to stop this PacketTransformer has begun.
      if (mediaType != null && !tlsPeerHasRaisedCloseNotifyWarning) {
        logger.error("Failed to send application data over DTLS transport: ", throwable);
      }
    }
  }

  /**
   * Sets the <tt>RTPConnector</tt> which is to use or uses this <tt>PacketTransformer</tt>.
   *
   * @param connector the <tt>RTPConnector</tt> which is to use or uses this
   *     <tt>PacketTransformer</tt>
   */
  void setConnector(AbstractRTPConnector connector) {
    if (this.connector != connector) {
      this.connector = connector;

      DatagramTransportImpl datagramTransport = this.datagramTransport;

      if (datagramTransport != null) datagramTransport.setConnector(connector);
    }
  }

  /**
   * Sets the <tt>MediaType</tt> of the stream which this instance is to work for/be associated
   * with.
   *
   * @param mediaType the <tt>MediaType</tt> of the stream which this instance is to work for/be
   *     associated with
   */
  synchronized void setMediaType(MediaType mediaType) {
    if (this.mediaType != mediaType) {
      MediaType oldValue = this.mediaType;

      this.mediaType = mediaType;

      if (oldValue != null) stop();
      if (this.mediaType != null) start();
    }
  }

  /**
   * Enables/disables rtcp-mux.
   *
   * @param rtcpmux whether to enable or disable.
   */
  void setRtcpmux(boolean rtcpmux) {
    this.rtcpmux = rtcpmux;
  }

  /**
   * Sets the DTLS protocol according to which this <tt>DtlsPacketTransformer</tt> is to act either
   * as a DTLS server or a DTLS client.
   *
   * @param setup the value of the <tt>setup</tt> SDP attribute to set on this instance in order to
   *     determine whether this instance is to act as a DTLS client or a DTLS server
   */
  void setSetup(DtlsControl.Setup setup) {
    if (this.setup != setup) this.setup = setup;
  }

  /** Starts this <tt>PacketTransformer</tt>. */
  private synchronized void start() {
    if (this.datagramTransport != null) {
      if (this.connectThread == null && dtlsTransport == null) {
        logger.warn(
            getClass().getName()
                + " has been started but has failed to establish"
                + " the DTLS connection!");
      }
      return;
    }

    if (rtcpmux && Component.RTCP == componentID) {
      // In the case of rtcp-mux, the RTCP transformer does not create
      // a DTLS session. The SRTP context (_srtpTransformer) will be
      // initialized on demand using initializeSRTCPTransformerFromRtp().
      return;
    }

    AbstractRTPConnector connector = this.connector;

    if (connector == null) throw new NullPointerException("connector");

    DtlsControl.Setup setup = this.setup;
    SecureRandom secureRandom = DtlsControlImpl.createSecureRandom();
    final DTLSProtocol dtlsProtocolObj;
    final TlsPeer tlsPeer;

    if (DtlsControl.Setup.ACTIVE.equals(setup)) {
      dtlsProtocolObj = new DTLSClientProtocol(secureRandom);
      tlsPeer = new TlsClientImpl(this);
    } else {
      dtlsProtocolObj = new DTLSServerProtocol(secureRandom);
      tlsPeer = new TlsServerImpl(this);
    }
    tlsPeerHasRaisedCloseNotifyWarning = false;

    final DatagramTransportImpl datagramTransport = new DatagramTransportImpl(componentID);

    datagramTransport.setConnector(connector);

    Thread connectThread =
        new Thread() {
          @Override
          public void run() {
            try {
              runInConnectThread(dtlsProtocolObj, tlsPeer, datagramTransport);
            } finally {
              if (Thread.currentThread().equals(DtlsPacketTransformer.this.connectThread)) {
                DtlsPacketTransformer.this.connectThread = null;
              }
            }
          }
        };

    connectThread.setDaemon(true);
    connectThread.setName(DtlsPacketTransformer.class.getName() + ".connectThread");

    this.connectThread = connectThread;
    this.datagramTransport = datagramTransport;

    boolean started = false;

    try {
      connectThread.start();
      started = true;
    } finally {
      if (!started) {
        if (connectThread.equals(this.connectThread)) this.connectThread = null;
        if (datagramTransport.equals(this.datagramTransport)) this.datagramTransport = null;
      }
    }

    notifyAll();
  }

  /** Stops this <tt>PacketTransformer</tt>. */
  private synchronized void stop() {
    if (connectThread != null) connectThread = null;
    try {
      // The dtlsTransport and _srtpTransformer SHOULD be closed, of
      // course. The datagramTransport MUST be closed.
      if (dtlsTransport != null) {
        try {
          dtlsTransport.close();
        } catch (IOException ioe) {
          logger.error("Failed to (properly) close " + dtlsTransport.getClass(), ioe);
        }
        dtlsTransport = null;
      }
      if (_srtpTransformer != null) {
        _srtpTransformer.close();
        _srtpTransformer = null;
      }
    } finally {
      try {
        closeDatagramTransport();
      } finally {
        notifyAll();
      }
    }
  }

  /** {@inheritDoc} */
  @Override
  public RawPacket transform(RawPacket pkt) {
    byte[] buf = pkt.getBuffer();
    int off = pkt.getOffset();
    int len = pkt.getLength();

    // If the specified pkt represents a DTLS record, then it should pass
    // through this PacketTransformer (e.g. it has been sent through
    // DatagramTransportImpl).
    if (isDtlsRecord(buf, off, len)) return pkt;

    // SRTP
    if (!transformEngine.isSrtpDisabled()) {
      // DTLS-SRTP has not been initialized yet or has failed to
      // initialize.
      SinglePacketTransformer srtpTransformer = waitInitializeAndGetSRTPTransformer();

      if (srtpTransformer != null) pkt = srtpTransformer.transform(pkt);
      else if (DROP_UNENCRYPTED_PKTS) pkt = null;
      // XXX Else, it is our explicit policy to let the received packet
      // pass through and rely on the SrtpListener to notify the user that
      // the session is not secured.
    }
    // Pure/non-SRTP DTLS
    else {
      // The specified pkt will pass through this PacketTransformer only
      // if it gets transformed into a DTLS record.
      pkt = null;

      sendApplicationData(buf, off, len);
    }
    return pkt;
  }

  /**
   * Gets the {@code SRTPTransformer} used by this instance. If {@link #_srtpTransformer} does not
   * exist (yet) and the state of this instance indicates that its initialization is in progess,
   * then blocks until {@code _srtpTransformer} is initialized and returns it.
   *
   * @return the {@code SRTPTransformer} used by this instance
   */
  private SinglePacketTransformer waitInitializeAndGetSRTPTransformer() {
    SinglePacketTransformer srtpTransformer = _srtpTransformer;

    if (srtpTransformer != null) return srtpTransformer;

    if (rtcpmux && Component.RTCP == componentID) return initializeSRTCPTransformerFromRtp();

    // XXX It is our explicit policy to rely on the SrtpListener to notify
    // the user that the session is not secure. Unfortunately, (1) the
    // SrtpListener is not supported by this DTLS SrtpControl implementation
    // and (2) encrypted packets may arrive soon enough to be let through
    // while _srtpTransformer is still initializing. Consequently, we will
    // block and wait for _srtpTransformer to initialize.
    boolean interrupted = false;

    try {
      synchronized (this) {
        do {
          srtpTransformer = _srtpTransformer;
          if (srtpTransformer != null) break; // _srtpTransformer is initialized

          if (connectThread == null) {
            // Though _srtpTransformer is NOT initialized, there is
            // no point in waiting because there is no one to
            // initialize it.
            break;
          }

          try {
            // It does not really matter (enough) how much we wait
            // here because we wait in a loop.
            long timeout = CONNECT_TRIES * CONNECT_RETRY_INTERVAL;

            wait(timeout);
          } catch (InterruptedException ie) {
            interrupted = true;
          }
        } while (true);
      }
    } finally {
      if (interrupted) Thread.currentThread().interrupt();
    }

    return srtpTransformer;
  }
}