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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.voting;
import org.gnunet.construct.FixedSizeIntegerArray;
import org.gnunet.construct.Message;
import org.gnunet.secretsharing.Parameters;
import java.math.BigInteger;
/**
* Proof in zero knowledge of dlog equality.
* Proves log_g(x) = log_h(y) = alpha
* FIXME: get the details right, the Cramers voting paper uses a proof that is a
* FIXME: bit different from the plain chaum pedersen proof
*/
public class ChaumPedersenZkp implements Message {
@FixedSizeIntegerArray(signed = true, bitSize = 8, length = Parameters.elgamalBits / 8)
public byte[] commit_a;
@FixedSizeIntegerArray(signed = true, bitSize = 8, length = Parameters.elgamalBits / 8)
public byte[] commit_b;
@FixedSizeIntegerArray(signed = true, bitSize = 8, length = Parameters.elgamalBits / 8)
public byte[] challenge_d;
@FixedSizeIntegerArray(signed = true, bitSize = 8, length = Parameters.elgamalBits / 8)
public byte[] response_r;
/**
* Verify the simulated proof. That is, don't check
* if the challenge was actually computed correctly from the commits.
*/
public boolean verifySim(BigInteger x, BigInteger y, BigInteger coeffG, BigInteger h) {
BigInteger a = new BigInteger(1, commit_a);
BigInteger b = new BigInteger(1, commit_b);
BigInteger d = new BigInteger(1, challenge_d);
BigInteger r = new BigInteger(1, response_r);
BigInteger g = Parameters.elgamalG;
BigInteger p = Parameters.elgamalP;
if (!b.equals(h.modPow(r, p).multiply(y.multiply(coeffG.modInverse(p)).modPow(d, p)).mod(p))) {
System.out.println("b not equal");
return false;
}
if (!a.equals(g.modPow(r, p).multiply(x.modPow(d, p)).mod(p))) {
System.out.println("a not equal");
return false;
}
return true;
}
}
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