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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., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.
*/
package org.gnunet.voting;
import org.gnunet.construct.FixedSizeIntegerArray;
import org.gnunet.construct.Message;
import org.gnunet.construct.UInt64;
import org.gnunet.construct.VariableSizeArray;
import org.gnunet.secretsharing.Parameters;
import java.math.BigInteger;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
/**
* Disjunction of Chaum Pedersen ZKPs.
*/
public class DisjunctionZkp implements Message {
@UInt64
public int numProofs;
@FixedSizeIntegerArray(signed = true, bitSize = 8, length = Parameters.elgamalBits / 8)
public byte[] challenge_c;
@VariableSizeArray(lengthField = "numProofs")
public ChaumPedersenZkp[] chaumPedersenZkps;
public boolean verifyChallenge() {
BigInteger c_actual = new BigInteger(1, challenge_c);
BigInteger c_expected = BigInteger.ZERO;
for (ChaumPedersenZkp chaumPedersenZkp : chaumPedersenZkps) {
BigInteger d = new BigInteger(1, chaumPedersenZkp.challenge_d);
c_expected = c_expected.add(d).mod(Parameters.elgamalQ);
}
return c_actual.equals(c_expected) && computeChallengeFromCommits().equals(c_actual);
}
public BigInteger computeChallengeFromCommits() {
MessageDigest digest;
try {
digest = MessageDigest.getInstance("SHA-512");
} catch (NoSuchAlgorithmException e) {
throw new RuntimeException("crypto algorithm 'SHA-512' required but not provided");
}
for (ChaumPedersenZkp chaumPedersenZkp : chaumPedersenZkps) {
digest.update(chaumPedersenZkp.commit_a);
digest.update(chaumPedersenZkp.commit_b);
}
return (new BigInteger(digest.digest())).mod(Parameters.elgamalQ);
}
}
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