resilientpool.java

与postgresql数据库结合的数据库水印软件包

/*
 * 
 * Copyright 2003,2004 The Watermill Team
 *
 * This file is part of Watermill.
 *
 *    Watermill 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 2 of the License, or
 *    (at your option) any later version.
 *
 *    Watermill 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 Watermill; if not, write to the Free Software
 *    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 */
package Watermill.kernel;

import java.io.*;
import java.util.*;

public class ResilientPool extends Pool implements Serializable {
    
    Identifiers identifiers;

    int lsb;
    int N;
    
    public ResilientPool(String ipn,Document id,WSchema iws) {
	super(ipn,id,iws);
	identifiers=id.getModifiableValuesIdentifiers(wschema.getLocalConstraints());
	lsb = 3;
	N = 10;
    }
    
    
    public Watermark watermark(Document doc,int seed) {
	// insert here a way to hash the seed
	Random r = new Random(seed);
	
	Watermark res = new Watermark();
	
	for(Enumeration e=identifiers.elements();e.hasMoreElements();){
	    Identifier id=(Identifier)e.nextElement();
	    // id contains key values and allowed distortions
	    r.setSeed(id.hashCode());
	    int p = r.nextInt(N);
	    if (p == 0) {
		int pos =  r.nextInt(lsb);
		int m = r.nextInt(2);
		int oldv = ((Value)(doc.getValue(id))).get();
		int newv;
		int d = 1 << pos;
		if ((oldv & d) > 0) { 
		    if (m == 0)
			res.put(id,new Value(-d));
		}
		else {
		    if (m == 1)
			res.put(id,new Value(d));
		}
	    }
	    
	}
	
	return res;
    }

}