/// <summary>
/// Creates a new encrypted vote.
/// </summary>
/// <remarks>
/// Includes zero-knowledge proof of vote being 0 or 1.
/// Still need non-interactive zero-knowledge proof of sum of votes.
/// </remarks>
/// <param name="votum">Actual vote.</param>
/// <param name="parameters">Cryptographic parameters.</param>
/// <param name="publicKey">Public key of the authorities.</param>
/// <param name="progress">Report the progress up.</param>
public Vote(int votum, BigInt nonce, BaseParameters parameters, BigInt publicKey, Progress progress)
{
if (!votum.InRange(0, 1))
throw new ArgumentException("Bad votum.");
if (nonce == null)
throw new ArgumentNullException("nonce");
if (parameters == null)
throw new ArgumentNullException("parameters");
if (publicKey == null)
throw new ArgumentNullException("publicKey");
P = parameters.P;
HalfKey = parameters.G.PowerMod(nonce, P);
//The 12 magic number is inserted to avoid division remainders when
//dividing partial deciphers for linear combinations by 2, 3 and 4.
Ciphertext = (publicKey.PowerMod(nonce * 12, P) * parameters.F.PowerMod(votum, P)).Mod(P);
RangeProves = new List<RangeProof>();
for (int proofIndex = 0; proofIndex < parameters.ProofCount; proofIndex++)
{
RangeProves.Add(new RangeProof(votum, nonce * 12, this, publicKey, parameters));
progress.Add(1d / (double)parameters.ProofCount);
}
}
/// <summary>
/// Creates a new ballot for a voter.
/// </summary>
/// <param name="vota">Vota the voter wishes to cast for each option.</param>
/// <param name="parameters">Cryptographic parameters.</param>
/// <param name="publicKey">Public key of voting authorities.</param>
/// <param name="progress">Report progress up.</param>
public Ballot(IEnumerable<int> vota, BaseParameters parameters, Question questionParameters, BigInt publicKey, Progress progress)
{
if (progress == null)
throw new ArgumentNullException("progress");
if (vota == null)
throw new ArgumentNullException("vota");
if (parameters == null)
throw new ArgumentNullException("parameters");
if (publicKey == null)
throw new ArgumentNullException("publicKey");
if (vota.Count() != questionParameters.Options.Count())
throw new ArgumentException("Bad vota.");
if (!vota.All(votum => votum.InRange(0, 1)))
throw new ArgumentException("Bad vota.");
if (vota.Sum() != questionParameters.MaxVota)
throw new ArgumentException("Bad vota.");
Votes = new List<Vote>();
BigInt nonceSum = new BigInt(0);
Vote voteSum = null;
List<Tuple<int, BigInt, BaseParameters, BigInt>> voteWorkList = new List<Tuple<int, BigInt, BaseParameters, BigInt>>();
foreach (int votum in vota)
{
BigInt nonce = parameters.Random();
nonceSum += nonce;
voteWorkList.Add(new Tuple<int, BigInt, BaseParameters, BigInt>(votum, nonce, parameters, publicKey));
}
progress.Down(1d / (vota.Count() + 1) * vota.Count());
List<Vote> voteList = Parallel
.Work<Tuple<int, BigInt, BaseParameters, BigInt>, Vote>(CreateVote, voteWorkList, progress.Set);
progress.Up();
foreach (Vote vote in voteList)
{
voteSum = voteSum == null ? vote : voteSum + vote;
Votes.Add(vote);
}
progress.Down(1d / (double)(vota.Count() + 1));
SumProves = new List<Proof>();
for (int proofIndex = 0; proofIndex < parameters.ProofCount; proofIndex++)
{
SumProves.Add(new Proof(nonceSum * 12, voteSum, publicKey, parameters));
progress.Add(1d / (double)parameters.ProofCount);
}
progress.Up();
}
/// <summary>
/// Verifies the correctness of the ballot.
/// </summary>
/// <remarks>
/// Verifies all proof for sum and range of votes.
/// </remarks>
/// <param name="publicKey">Public key of the authorities.</param>
/// <param name="parameters">Cryptographic parameters.</param>
/// <param name="questionParameters">Parameters of the question.</param>
/// <param name="rng">Random number generator.</param>
/// <param name="proofCheckCount">Number of proofs to check.</param>
/// <param name="progress">Reports on the progress.</param>
/// <returns>Result of the verification.</returns>
public bool Verify(BigInt publicKey, BaseParameters parameters, Question questionParameters, RandomNumberGenerator rng, int proofCheckCount, Progress progress)
{
if (publicKey == null)
throw new ArgumentNullException("publicKey");
if (parameters == null)
throw new ArgumentNullException("parameters");
if (questionParameters == null)
throw new ArgumentNullException("questionParameters");
bool verifies = true;
Vote voteSum = null;
CryptoLog.Begin(CryptoLogLevel.Detailed, "Verifying ballot");
CryptoLog.Add(CryptoLogLevel.Detailed, "Question", questionParameters.Text.Text);
foreach (Vote vote in Votes)
{
verifies &= vote.Verify(publicKey, parameters, rng, proofCheckCount);
voteSum = voteSum == null ? vote : voteSum + vote;
progress.Add(1d / (double)Votes.Count);
}
verifies &= SumProves.Count == parameters.ProofCount;
verifies &= SumProves
.SelectRandom(rng, proofCheckCount)
.All(sumProof => sumProof.Verify(voteSum, publicKey, parameters, questionParameters));
CryptoLog.Add(CryptoLogLevel.Numeric, "Public key", publicKey);
CryptoLog.Add(CryptoLogLevel.Numeric, "Vote sum ciphertext", voteSum.Ciphertext);
CryptoLog.Add(CryptoLogLevel.Numeric, "Vote sum halfkey", voteSum.HalfKey);
CryptoLog.Add(CryptoLogLevel.Detailed, "Verified", verifies);
CryptoLog.End(CryptoLogLevel.Detailed);
return verifies;
}
