MixPlugIn.java

/*******************************************************************************
 * gMix open source project - https://svs.informatik.uni-hamburg.de/gmix/
 * Copyright (C) 2014  SVS
 *
 * 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 userGeneratedContent.testbedPlugIns.layerPlugIns.layer3outputStrategy.cottrellPool_v0_001;

import java.security.SecureRandom;

import staticContent.framework.controller.Implementation;
import staticContent.framework.interfaces.Layer3OutputStrategyMix;
import staticContent.framework.message.MixMessage;
import staticContent.framework.message.Reply;
import staticContent.framework.message.Request;
import staticContent.framework.userDatabase.User;


//Cottrell 1995 ("Mixmaster & Remailer Attacks")
//collect incoming messages until "poolSize" messages are reached
//for each further message:
//put new message in pool and randomly chose and put out one message 
//see also: ThresholdPool.java (CottrellPool is a ThresholdPool with n=1)
public class MixPlugIn extends Implementation implements Layer3OutputStrategyMix {

	private static SecureRandom secureRandom = new SecureRandom();
	private SimplexCottrellPool requestPool;
	private SimplexCottrellPool replyPool;
	private int POOL_SIZE;
	
	
	@Override
	public void constructor() {
		this.POOL_SIZE = settings.getPropertyAsInt("COTTRELL_POOL_POOL_SIZE");
		this.requestPool = new SimplexCottrellPool(true);
		this.replyPool = new SimplexCottrellPool(false);
	}
	
	
	@Override
	public void initialize() {
		// no need to do anything
	}

	
	@Override
	public void begin() {
		// no need to do anything
	}

	
	@Override
	public void addRequest(Request request) {
		requestPool.addMessage((MixMessage) request);
	}

	
	@Override
	public void addReply(Reply reply) {
		replyPool.addMessage((MixMessage) reply);
	}

	
	public class SimplexCottrellPool {

		private boolean isRequestPool;
		private MixMessage[] collectedMessages;
		private int nextFreeSlot = 0;

		
		public SimplexCottrellPool(boolean isRequestPool) {
			this.collectedMessages = new MixMessage[POOL_SIZE];
			this.isRequestPool = isRequestPool;
		}
		
		
		public void addMessage(MixMessage mixMessage) {
			synchronized (this) {
				if (nextFreeSlot < POOL_SIZE) {
					collectedMessages[nextFreeSlot++] = mixMessage;
				} else {
					int chosen = secureRandom.nextInt(POOL_SIZE+1);
					if (chosen == POOL_SIZE) {
						putOutMessage(mixMessage);
					} else {
						putOutMessage(collectedMessages[chosen]);
						collectedMessages[chosen] = mixMessage;
					}
				}
			}
		}

		private void putOutMessage(MixMessage mixMessage) {
			if (isRequestPool)
				anonNode.putOutRequest((Request)mixMessage);
			else
				anonNode.putOutReply((Reply)mixMessage);
		}
			
	}

	
	@Override
	public int getMaxSizeOfNextWrite() {
		return super.recodingLayerMix.getMaxSizeOfNextReply();
	}


	@Override
	public int getMaxSizeOfNextRead() {
		return super.recodingLayerMix.getMaxSizeOfNextRequest();
	}


	@Override
	public void write(User user, byte[] data) {
		Reply reply = MixMessage.getInstanceReply(data, user); 
		reply.isFirstReplyHop = true;
		transportLayerMix.addLayer4Header(reply);
		anonNode.forwardToLayer2(reply);
	}
	
}