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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 com.google.common.base.Optional;
import org.gnunet.construct.Construct;
import org.gnunet.construct.Message;
import org.gnunet.construct.NestedMessage;
import org.gnunet.secretsharing.Ciphertext;
import org.gnunet.secretsharing.Parameters;
import org.gnunet.secretsharing.ThresholdPublicKey;
import org.gnunet.util.BigIntegers;
import org.gnunet.util.Configuration;
import org.gnunet.util.Strings;
import org.gnunet.util.crypto.EcdsaPublicKey;
import org.gnunet.util.crypto.SignedContentMessage;
import java.math.BigInteger;
import java.util.Arrays;
public class EncryptedVote implements Message, SignedContentMessage {
@NestedMessage
public Ciphertext v;
@NestedMessage
public DisjunctionZkp disjunctionZkp;
@NestedMessage
public EcdsaPublicKey voterPublicKey;
/**
* Construct an EncryptedVote by parsing it from the configuration.
* The voter public key must be passed separately.
*
* @param cfg configuration
* @param voterPublicKey public key of the voter
* @return the encrypted vote
*/
public static EncryptedVote parseFromConfiguration(Configuration cfg, EcdsaPublicKey voterPublicKey) {
Optional<String> optVal = cfg.getValueString("vote", "ENCRYPTED_VOTE_VAL");
if (!optVal.isPresent()) {
return null;
}
Optional<String> optZkp = cfg.getValueString("vote", "ZKP");
if (!optZkp.isPresent()) {
return null;
}
EncryptedVote encryptedVote = new EncryptedVote();
encryptedVote.voterPublicKey = voterPublicKey;
encryptedVote.v = Ciphertext.fromString(optVal.get());
System.out.println("reading, string size " + optZkp.get().length());
byte[] zkpData = Strings.stringToData(optZkp.get());
if (null == zkpData) {
throw new InvalidBallotException("could not read ZKP from ballot");
}
encryptedVote.disjunctionZkp = Construct.parseAs(zkpData, DisjunctionZkp.class);
return encryptedVote;
}
public static EncryptedVote fromChoice(int choiceId, ThresholdPublicKey thresholdPublicKey, EcdsaPublicKey voterPublicKey,
BigInteger[] generators) {
EncryptedVote encryptedVote = new EncryptedVote();
encryptedVote.v = new Ciphertext();
encryptedVote.voterPublicKey = voterPublicKey;
encryptedVote.disjunctionZkp = new DisjunctionZkp();
encryptedVote.disjunctionZkp.chaumPedersenZkps = new ChaumPedersenZkp[generators.length];
encryptedVote.disjunctionZkp.numProofs = generators.length;
// the discrete logarithm
BigInteger alpha = Parameters.randomQ();
// the secret for the ZKP
BigInteger w = Parameters.randomQ();
BigInteger h = new BigInteger(1, thresholdPublicKey.bits);
BigInteger g = Parameters.elgamalG;
BigInteger p = Parameters.elgamalP;
BigInteger q = Parameters.elgamalQ;
BigInteger x = Parameters.modPowG(alpha);
BigInteger y = h.modPow(alpha, p).multiply(generators[choiceId]).mod(p);
encryptedVote.v.c_1 = BigIntegers.serializeUnsigned(x, Parameters.elgamalBits);
encryptedVote.v.c_2 = BigIntegers.serializeUnsigned(y, Parameters.elgamalBits);
// sum of all the simulation challenges
BigInteger d_sim_sum = BigInteger.ZERO;
// generate simulated proofs
for (int i = 0; i < generators.length; i++) {
if (i == choiceId) {
continue;
}
BigInteger r = Parameters.randomQ();
BigInteger d = Parameters.randomQ();
BigInteger a = g.modPow(r, p).multiply(x.modPow(d, p)).mod(p);
BigInteger b = h.modPow(r, p).multiply(y.multiply(generators[i].modInverse(p)).modPow(d, p)).mod(p);
d_sim_sum = d_sim_sum.add(d);
ChaumPedersenZkp zkp = new ChaumPedersenZkp();
zkp.challenge_d = BigIntegers.serializeUnsigned(d, Parameters.elgamalBits);
zkp.response_r = BigIntegers.serializeUnsigned(r, Parameters.elgamalBits);
zkp.commit_a = BigIntegers.serializeUnsigned(a, Parameters.elgamalBits);
zkp.commit_b = BigIntegers.serializeUnsigned(b, Parameters.elgamalBits);
if (!zkp.verifySim(x, y, generators[i], h)) {
throw new AssertionError("crypto not working");
}
encryptedVote.disjunctionZkp.chaumPedersenZkps[i] = zkp;
}
ChaumPedersenZkp zkp = new ChaumPedersenZkp();
encryptedVote.disjunctionZkp.chaumPedersenZkps[choiceId] = zkp;
BigInteger a = g.modPow(w, p);
BigInteger b = h.modPow(w, p);
zkp.commit_a = BigIntegers.serializeUnsigned(a, Parameters.elgamalBits);
zkp.commit_b = BigIntegers.serializeUnsigned(b, Parameters.elgamalBits);
BigInteger c = encryptedVote.disjunctionZkp.computeChallengeFromCommits();
BigInteger d = c.subtract(d_sim_sum).mod(q);
BigInteger r = w.subtract(alpha.multiply(d)).mod(q);
zkp.challenge_d = BigIntegers.serializeUnsigned(d, Parameters.elgamalBits);
zkp.response_r = BigIntegers.serializeUnsigned(r, Parameters.elgamalBits);
if (!zkp.verifySim(x,y,generators[choiceId], h)) {
throw new AssertionError("crypto (2) not working");
}
encryptedVote.disjunctionZkp.challenge_c = BigIntegers.serializeUnsigned(c, Parameters.elgamalBits);
if (!encryptedVote.disjunctionZkp.verifyChallenge()) {
throw new AssertionError("crypto not working (3)");
}
return encryptedVote;
}
public void writeToConfiguration(Configuration cfg) {
cfg.setValueString("vote", "ENCRYPTED_VOTE_VAL", v.toString());
byte[] zkpData = Construct.toBinary(disjunctionZkp);
String zkpString = Strings.dataToString(zkpData);
if (zkpString.length() != Strings.getEncodedStringLength(zkpData.length))
throw new AssertionError("fail");
if (zkpData.length != Strings.getDecodedDataLength(zkpString.length()))
throw new AssertionError("fail, got " + zkpData.length + " expected " +
Strings.getDecodedDataLength(zkpString.length()) + "for string length" + zkpString.length());
System.out.println("everyting ok, size binary size" + zkpData.length +" str size " + zkpString.length());
byte[] zkpData2 = Strings.stringToData(zkpString);
if (!Arrays.equals(zkpData, zkpData2)) {
throw new AssertionError("something wrong");
}
System.out.println("everyting ok, size binary size" + zkpData.length +" str size " + zkpString.length());
cfg.setValueString("vote", "ZKP", zkpString);
}
public boolean verify() {
return false;
}
}
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