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/*
This file is part of GNUnet.
Copyright (C) 2014 Christian Grothoff (and other contributing authors)
GNUnet 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, or (at your
option) any later version.
GNUnet 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 GNUnet; see the file COPYING. If not, write to the
Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
Boston, MA 02110-1301, USA.
*/
package org.gnunet.secretsharing;
import org.gnunet.construct.FixedSizeIntegerArray;
import org.gnunet.construct.Message;
import org.gnunet.util.BigIntegers;
import org.gnunet.util.Strings;
import java.math.BigInteger;
import java.util.Arrays;
/**
* ElGamal ciphertext.
*/
public class Ciphertext implements Message {
@FixedSizeIntegerArray(signed = true, bitSize = 8, length = Parameters.elgamalBits / 8)
public byte[] c_1;
@FixedSizeIntegerArray(signed = true, bitSize = 8, length = Parameters.elgamalBits / 8)
public byte[] c_2;
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Ciphertext that = (Ciphertext) o;
if (!Arrays.equals(c_1, that.c_1)) return false;
if (!Arrays.equals(c_2, that.c_2)) return false;
return true;
}
@Override
public int hashCode() {
int result = c_1 != null ? Arrays.hashCode(c_1) : 0;
result = 31 * result + (c_2 != null ? Arrays.hashCode(c_2) : 0);
return result;
}
/**
* Allocate the ciphertext with zeros.
*/
public void allocate() {
c_1 = new byte[Parameters.elgamalBits / 8];
c_2 = new byte[Parameters.elgamalBits / 8];
}
@Override
public String toString() {
byte[] allBytes = new byte[c_1.length + c_2.length];
System.arraycopy(c_1, 0, allBytes, 0, c_1.length);
System.arraycopy(c_2, 0, allBytes, c_1.length, c_2.length);
return Strings.dataToString(allBytes);
}
public static Ciphertext fromString(String s) {
byte[] allBytes = new byte[2 * Parameters.elgamalBits / 8];
if (!Strings.stringToData(s, allBytes))
return null;
Ciphertext ciphertext = new Ciphertext();
ciphertext.allocate();
System.arraycopy(allBytes, 0, ciphertext.c_1, 0, ciphertext.c_1.length);
System.arraycopy(allBytes, ciphertext.c_1.length, ciphertext.c_2, 0, ciphertext.c_2.length);
return ciphertext;
}
/**
* Multiply two elgamal ciphertexts.
*
* @param v the other ciphertext
* @return the product of two ciphertexts
*/
public Ciphertext multiply(Ciphertext v) {
BigInteger xc_1 = new BigInteger(1, this.c_1);
BigInteger xc_2 = new BigInteger(1, this.c_2);
BigInteger yc_1 = new BigInteger(1, v.c_1);
BigInteger yc_2 = new BigInteger(1, v.c_2);
Ciphertext ciphertext = new Ciphertext();
ciphertext.c_1 = BigIntegers.serializeUnsigned(xc_1.multiply(yc_1).mod(Parameters.elgamalP),
Parameters.elgamalBits);
ciphertext.c_2 = BigIntegers.serializeUnsigned(xc_2.multiply(yc_2).mod(Parameters.elgamalP),
Parameters.elgamalBits);
return ciphertext;
}
/**
* Get the ciphertext that is the identity for multiplication.
*
* @return multiplicative identity ciphertext
*/
public static Ciphertext identity() {
Ciphertext ciphertext = new Ciphertext();
ciphertext.allocate();
ciphertext.c_1 = BigIntegers.serializeUnsigned(BigInteger.ONE, Parameters.elgamalBits);
ciphertext.c_2 = BigIntegers.serializeUnsigned(BigInteger.ONE, Parameters.elgamalBits);
return ciphertext;
}
}
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