/*******************************************************************************

"FreePastry" Peer-to-Peer Application Development Substrate

Copyright 2002-2007, Rice University. Copyright 2006-2007, Max Planck Institute 
for Software Systems.  All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:

- Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.

- Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.

- Neither the name of Rice  University (RICE), Max Planck Institute for Software 
Systems (MPI-SWS) nor the names of its contributors may be used to endorse or 
promote products derived from this software without specific prior written 
permission.

This software is provided by RICE, MPI-SWS and the contributors on an "as is" 
basis, without any representations or warranties of any kind, express or implied 
including, but not limited to, representations or warranties of 
non-infringement, merchantability or fitness for a particular purpose. In no 
event shall RICE, MPI-SWS or contributors be liable for any direct, indirect, 
incidental, special, exemplary, or consequential damages (including, but not 
limited to, procurement of substitute goods or services; loss of use, data, or 
profits; or business interruption) however caused and on any theory of 
liability, whether in contract, strict liability, or tort (including negligence
or otherwise) arising in any way out of the use of this software, even if 
advised of the possibility of such damage.

*******************************************************************************/ 
package org.mpisws.p2p.transport.rc4;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.security.GeneralSecurityException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Map;

import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;
import javax.security.sasl.AuthenticationException;

import org.mpisws.p2p.transport.ClosedChannelException;
import org.mpisws.p2p.transport.ErrorHandler;
import org.mpisws.p2p.transport.MessageCallback;
import org.mpisws.p2p.transport.MessageRequestHandle;
import org.mpisws.p2p.transport.P2PSocket;
import org.mpisws.p2p.transport.P2PSocketReceiver;
import org.mpisws.p2p.transport.SocketCallback;
import org.mpisws.p2p.transport.SocketRequestHandle;
import org.mpisws.p2p.transport.TransportLayer;
import org.mpisws.p2p.transport.TransportLayerCallback;
import org.mpisws.p2p.transport.util.SocketRequestHandleImpl;

import rice.environment.Environment;
import rice.environment.logging.Logger;
import rice.environment.random.RandomSource;
import rice.p2p.commonapi.IdFactory;
import rice.pastry.commonapi.PastryIdFactory;

/**
 * Only encrypts socket traffic!!!
 * 
 * Encrypts channels based on a password.
 * 
 * Builds a session password for each socket which is a hash of the user-defined password and a clear-text seed.
 * 
 * Note that the seed length isn't sent in the protocol, so it must be the same on all peers.
 * 
 * Why do we need a password seed?  Imagine a protocol where you contact a peer and it returns a boolean.  
 * W/O a seed, the protocol would only return 2 possible messages.  While you may not know which is which, you could probably figure it
 * out by seeing who returns what.  
 * 
 * Both sides need to have a different seed, so that under a simple agreement protocol, you can't easily see a replay.
 * 
 * E.G:
 *   A -> B: 14  // I propose 14
 *   B -> A: 14  // I agree to 14, in this case an evesdropper could determine whether or not B agreed with A, which is a leak of info
 * 
 * Here's the Seed protocol we use:
 * 
 * // pw is a pre-established password 
 * A -> B: SeedB
 * B -> E(H(pw,SeedB))[SeedA,SeedB]
 *  // Now A and B each have an agreed upon seed
 *  // Note that it may be important in step 2 to send SeedA before SeedB, otherwise, an attacker could keep sending new SeedB, 
 *  // and maybe learn something about the first packet... but maybe this doesn't matter because of the Hashing to generate the secret key
 * 
 * @author Jeff Hoye
 *
 * @param <Identifier>
 * @param <MsgType>
 */
public class RC4TransportLayer<Identifier, MsgType> implements TransportLayer<Identifier,MsgType>, TransportLayerCallback<Identifier, MsgType> {
  /**
   * Default 1
   * 1 = encrypt
   * 0 = don't encrypt
   * 
   * Need to implemet this before we add it to the API
   */
//  public static final String ENCRYPT_SOCKET = "encrypt_socket";
  
  protected TransportLayer<Identifier,MsgType> tl;
  protected TransportLayerCallback<Identifier, MsgType> callback;
  
  protected Environment env;
  protected Logger logger;

  protected ErrorHandler<Identifier> errorHandler;
  
  protected MessageDigest md;

  public static final int KEY_LENGTH = 16;
  
  byte[] password;
  int PW_SEED_LENGTH;
  int WRITE_BUFFER_SIZE = 1024;
  RandomSource random;

  public RC4TransportLayer(TransportLayer<Identifier,MsgType> tl, Environment env, String password, ErrorHandler<Identifier> errorHandler) throws NoSuchAlgorithmException {
    this(tl,env,password,KEY_LENGTH,env.getRandomSource(), errorHandler);
  }

  public RC4TransportLayer(TransportLayer<Identifier,MsgType> tl, Environment env, String password, int pwSeedLength, RandomSource random, ErrorHandler<Identifier> errorHandler) throws NoSuchAlgorithmException {
    this.tl = tl;
    this.tl.setCallback(this);
    this.env=env; 
    this.password = password.getBytes();
    this.PW_SEED_LENGTH = pwSeedLength;
    this.logger=env.getLogManager().getLogger(RC4TransportLayer.class, null);
    this.random = random;
    this.errorHandler = errorHandler;
//    try {
      md = MessageDigest.getInstance("SHA");
//    } catch ( NoSuchAlgorithmException e ) {
//      Logger logger = env.getLogManager().getLogger(getClass(), null);
//      if (logger.level <= Logger.SEVERE) logger.log(
//        "No SHA support!" );
//    }

  }
  
  public void acceptMessages(boolean b) {
    tl.acceptMessages(b);
  }

  public void acceptSockets(boolean b) {
    tl.acceptSockets(b);
  }

  public Identifier getLocalIdentifier() {
    return tl.getLocalIdentifier();
  }

  public SocketRequestHandle<Identifier> openSocket(final Identifier i,
      final SocketCallback<Identifier> deliverSocketToMe, final Map<String, Object> options) {
    
    // this allows suppression of the encryption, but no notification of whether it should/shouldn't be encrypted, so you have to 
    // predetermine this...  maybe this isn't possible?
    // TODO: Send a byte wheter this is encrypted or not, and record this on the other end
//    if (options != null && options.containsKey(ENCRYPT_SOCKET) && ((Integer)options.get(ENCRYPT_SOCKET) == 0)) {
//      // don't encrypt the socket
//      return tl.openSocket(i, deliverSocketToMe, options);
//    }
    
    final SocketRequestHandleImpl<Identifier> ret = new SocketRequestHandleImpl<Identifier>(i,options,logger);
    
    ret.setSubCancellable(tl.openSocket(i, new SocketCallback<Identifier>() {

      public void receiveException(SocketRequestHandle<Identifier> s,
          Exception ex) {
        deliverSocketToMe.receiveException(s, ex);
      }

      public void receiveResult(SocketRequestHandle<Identifier> cancellable,
          P2PSocket<Identifier> sock) {
        
        // write the decrypt seed to B
        final byte[] decryptSeed = new byte[PW_SEED_LENGTH];
        random.nextBytes(decryptSeed);
        
        P2PSocketReceiver<Identifier> writeDecryptSeedReceiver = new P2PSocketReceiver<Identifier>() {
          ByteBuffer dsBB = ByteBuffer.wrap(decryptSeed);

          public void receiveSelectResult(P2PSocket<Identifier> socket,
              boolean canRead, boolean canWrite) throws IOException {
            long bytesWritten = socket.write(dsBB);
            if (bytesWritten < 0) {
              socket.close();
              deliverSocketToMe.receiveException(ret, new ClosedChannelException("Socket to "+i+" closed by remote host. "+ret));
              return;
            }
            if (dsBB.hasRemaining()) {
              // need to finish writing
              socket.register(false, true, this);
              return;
            }

            // build the key
            byte[] decryptKeyBytes = new byte[KEY_LENGTH];
            synchronized(md) {
              md.update(password);
              md.update(decryptSeed);
              System.arraycopy(md.digest(), 0, decryptKeyBytes, 0, KEY_LENGTH);
            }
            SecretKey decryptKey = new SecretKeySpec(decryptKeyBytes, ALGORITHM);
            try {
              final Cipher decryptCipher = Cipher.getInstance(ALGORITHM);
              decryptCipher.init(Cipher.DECRYPT_MODE, decryptKey);
              // decrypt/read the response
              P2PSocketReceiver<Identifier> readEncryptSeedReceiver = new P2PSocketReceiver<Identifier>() {
                ByteBuffer encryptedSeeds = ByteBuffer.allocate(PW_SEED_LENGTH*2); // Because we have to verify that SeedB is properly encrypted
                public void receiveSelectResult(P2PSocket<Identifier> socket,
                    boolean canRead, boolean canWrite) throws IOException {
                  long bytesRead = socket.read(encryptedSeeds);
                  if (bytesRead < 0) {
                    socket.close();
                    deliverSocketToMe.receiveException(ret, new ClosedChannelException("Socket to "+i+" closed by remote host. "+ret));
                    return;
                  }
                  if (encryptedSeeds.hasRemaining()) {
                    // need to finish reading
                    socket.register(true, false, this);
                    return;
                  }
                  
                  // decrypt the keys
                  byte[] decryptedSeeds = decryptCipher.update(encryptedSeeds.array());
                  
                  // make sure decryptSeed == the second key in decryptedSeeds
                  boolean same = true;
                  for (int ctr = 0; ctr < PW_SEED_LENGTH; ctr++) {
                    if (decryptedSeeds[ctr+PW_SEED_LENGTH] != decryptSeed[ctr]) {
                      same = false;
                      break;
                    }
                  }
                  if (!same) {
                    socket.close();
                    deliverSocketToMe.receiveException(ret, new AuthenticationException("Counterpart failed to properly encrypt his encryptSeed in the message."));
                    return;
                  }

                  // copy out the encryptSeed
                  byte[] encryptSeed = new byte[PW_SEED_LENGTH];
                  System.arraycopy(decryptedSeeds, 0, encryptSeed, 0, PW_SEED_LENGTH);
                  
                  // build the encrypt key
                  byte[] encryptKeyBytes = new byte[KEY_LENGTH];
                  synchronized(md) {
                    md.update(password);
                    md.update(encryptSeed);
                    System.arraycopy(md.digest(), 0, encryptKeyBytes, 0, KEY_LENGTH);
                  }
                  SecretKey encryptKey = new SecretKeySpec(encryptKeyBytes, ALGORITHM);
                  try {
                    Cipher encryptCipher = Cipher.getInstance(ALGORITHM);
                    encryptCipher.init(Cipher.ENCRYPT_MODE, encryptKey);
                    deliverSocketToMe.receiveResult(ret, new EncryptedSocket<Identifier>(i,socket,logger,options,encryptCipher,decryptCipher,WRITE_BUFFER_SIZE));
                  } catch (GeneralSecurityException gse) {
                    socket.close();
                    deliverSocketToMe.receiveException(ret, gse);
                  }            
                }
  
                public void receiveException(P2PSocket<Identifier> socket,
                    Exception ioe) {
                  deliverSocketToMe.receiveException(ret, ioe);
                }
              };
              readEncryptSeedReceiver.receiveSelectResult(socket, true, false);
            } catch (GeneralSecurityException gse) {
              socket.close();
              deliverSocketToMe.receiveException(ret, gse);
            }            
          }
          
          public void receiveException(P2PSocket<Identifier> socket,
              Exception ioe) {
            deliverSocketToMe.receiveException(ret, ioe);
          }
        };
        try {
          writeDecryptSeedReceiver.receiveSelectResult(sock, false, true);
        } catch (IOException ioe) {
          deliverSocketToMe.receiveException(ret, ioe);
        }        
      }    
    }, options));
    
    return ret;
  }
  
  public void incomingSocket(P2PSocket<Identifier> s) throws IOException {
    // read the encryptSeed in plaintext
    // generate the encryptCipher
    // generate a decryptSeed
    // generate the decryptCipher
    // encrypt the decryptSeed+encryptSeed
    // send them
    // build the Encrypted Socket

    new P2PSocketReceiver<Identifier>() {
      byte[] encryptSeed = new byte[PW_SEED_LENGTH];
      ByteBuffer encryptSeedBuffer = ByteBuffer.wrap(encryptSeed);
      
      public void receiveSelectResult(P2PSocket<Identifier> socket,
          boolean canRead, boolean canWrite) throws IOException {
        // read the encryptSeedBuffer until it is full
        long ret = socket.read(encryptSeedBuffer);
        if (ret < 0) {
          socket.close();
        }
        if (encryptSeedBuffer.hasRemaining()) {
          socket.register(true, false, this);
          return;
        }
        
        // build the encrypt key
        byte[] encryptKeyBytes = new byte[KEY_LENGTH];
        synchronized(md) {
          md.update(password);
          md.update(encryptSeed);
          System.arraycopy(md.digest(), 0, encryptKeyBytes, 0, KEY_LENGTH);
        }
        SecretKey encryptKey = new SecretKeySpec(encryptKeyBytes, ALGORITHM);
        try {
          final Cipher encryptCipher = Cipher.getInstance(ALGORITHM);
          encryptCipher.init(Cipher.ENCRYPT_MODE, encryptKey);
          
          // write the decrypt seed to A
          final byte[] decryptSeed = new byte[PW_SEED_LENGTH];
          random.nextBytes(decryptSeed);
          
          // build the key
          byte[] decryptKeyBytes = new byte[KEY_LENGTH];
          synchronized(md) {
            md.update(password);
            md.update(decryptSeed);
            System.arraycopy(md.digest(), 0, decryptKeyBytes, 0, KEY_LENGTH);
          }
          SecretKey decryptKey = new SecretKeySpec(decryptKeyBytes, ALGORITHM);
          final Cipher decryptCipher = Cipher.getInstance(ALGORITHM);
          decryptCipher.init(Cipher.DECRYPT_MODE, decryptKey);
          
          // encrypt the seeds
          byte[] encryptedSeeds = new byte[PW_SEED_LENGTH*2];
          encryptCipher.update(decryptSeed,0,PW_SEED_LENGTH,encryptedSeeds,0);
          encryptCipher.update(encryptSeed,0,PW_SEED_LENGTH,encryptedSeeds,PW_SEED_LENGTH);
          
          // write the encrypted seeds
          final ByteBuffer encryptedSeedsBuffer = ByteBuffer.wrap(encryptedSeeds);
          new P2PSocketReceiver<Identifier>() {

            public void receiveSelectResult(P2PSocket<Identifier> socket,
                boolean canRead, boolean canWrite) throws IOException {
              long ret = socket.write(encryptedSeedsBuffer);
              if (ret < 0) {
                receiveException(socket, new ClosedChannelException("Channel closed while establishing crypto. "+socket));
                return;
              }
              if (encryptedSeedsBuffer.hasRemaining()) {
                socket.register(false, true, this);
                return;
              }
              
              // we're done...
              callback.incomingSocket(new EncryptedSocket<Identifier>(socket.getIdentifier(),socket,logger,socket.getOptions(),encryptCipher,decryptCipher,WRITE_BUFFER_SIZE));
            }
            
            public void receiveException(P2PSocket<Identifier> socket,
                Exception ioe) {
              errorHandler.receivedException(socket.getIdentifier(), ioe);
              socket.close();
            }            
          }.receiveSelectResult(socket, false, true);
          
          
        } catch (GeneralSecurityException gse) {
          socket.close();
        }            

      }
    
      public void receiveException(P2PSocket<Identifier> socket, Exception ioe) {
        errorHandler.receivedException(socket.getIdentifier(), ioe);
        socket.close();
      }

    }.receiveSelectResult(s,true,false);
  }

  public MessageRequestHandle<Identifier, MsgType> sendMessage(Identifier i,
      MsgType m, MessageCallback<Identifier, MsgType> deliverAckToMe,
      Map<String, Object> options) {
    return tl.sendMessage(i, m, deliverAckToMe, options);
  }

  public void setCallback(TransportLayerCallback<Identifier, MsgType> callback) {
    this.callback = callback;
  }

  public void setErrorHandler(ErrorHandler<Identifier> handler) {
    this.errorHandler = handler;
  }

  public void destroy() {
    // TODO Auto-generated method stub
    
  }

  public void messageReceived(Identifier i, MsgType m,
      Map<String, Object> options) throws IOException {
    callback.messageReceived(i, m, options);
  }

  private static final String ALGORITHM = "RC4";
}
