private void ConstructorHelper(ProverSetMembershipParameters prover, SetMembershipProofGenerationRandomData smRandom = null)
{
try
{
// check that parameters can be used to construct valid proof.
if (!prover.Verify())
{
throw new ArgumentException("Invalid proof parameters. Cannot create proof");
}
// set Group context
this.Group = prover.Group;
this.IsGroupSerializable = true;
// allocate space for proof
this.c = new FieldZqElement[prover.MemberSet.Length - 1];
this.a = new GroupElement[prover.MemberSet.Length];
this.r = new FieldZqElement[prover.MemberSet.Length];
// generate random values needed for proof
if (smRandom == null)
{
// generate a pair of random values for each fake proofs, plus the random exponent for the real one
smRandom = SetMembershipProofGenerationRandomData.Generate(prover.FieldZq, prover.MemberSet.Length - 1);
}
// Find index of prover.OpenCommitment.CommittedValue in prover.MemberSet
int indexOfCommittedValue = prover.IndexOfCommittedValueInSet;
// generate a fake proof for each prover.MemberSet element that is not
// equal to CommitedValue.
FieldZqElement sumOfSubChallenges = prover.FieldZq.Zero;
int randomIndex = 0;
for (int index = 0; index < prover.MemberSet.Length; ++index)
{
if (index != indexOfCommittedValue)
{
this.generateFakeProof(index, prover, smRandom.c[randomIndex], smRandom.r[randomIndex]);
sumOfSubChallenges += smRandom.c[randomIndex];
randomIndex++;
}
}
// generate challenge, and a real proof for committment.CommittedValue
this.generateRealA(indexOfCommittedValue, prover, smRandom.w);
FieldZqElement challenge = this.ComputeChallenge(prover);
this.generateRealProof(indexOfCommittedValue, prover, smRandom.w, sumOfSubChallenges.Negate() + challenge);
}
catch (Exception e)
{
throw new Exception("Could not create SetMembershipProof.", e);
}
}
/// <summary>
/// Generates a set membership proof from U-Prove parameters.
/// </summary>
/// <param name="pppp">The prover presentation protocol parameters.</param>
/// <param name="pp">The presentation proof.</param>
/// <param name="cpv">The commitment private values returned when generating the presentation proof.</param>
/// <param name="committedIndex">Index of the committed attribute used to generate the set membership proof.</param>
/// <param name="setValues">Set values to prove against.</param>
/// <param name="smRandom">Optional pregenerated random values, or <c>null</c>.</param>
/// <returns>A set membership proof.</returns>
public static SetMembershipProof Generate(ProverPresentationProtocolParameters pppp, PresentationProof pp, CommitmentPrivateValues cpv, int committedIndex, byte[][] setValues, SetMembershipProofGenerationRandomData smRandom = null)
{
// get the index of the commitment to use, given the underlying attribute's index
int commitmentIndex = ClosedPedersenCommitment.GetCommitmentIndex(pppp.Committed, committedIndex);
// generate the membership proof
ProverSetMembershipParameters setProver =
new ProverSetMembershipParameters(
new PedersenCommitment(pppp, pp, cpv, commitmentIndex),
VerifierSetMembershipParameters.GenerateMemberSet(pppp.IP, committedIndex, setValues),
new CryptoParameters(pppp.IP));
return(new SetMembershipProof(setProver, smRandom));
}
/// <summary>
/// Constructor. Creates a proof that a token attribute is in a given set.
/// </summary>
/// <param name="prover">Token description.</param>
/// <param name="attributeIndexForProver">1-based attribute index in token.</param>
/// <param name="setValues">Set of attributes to compare to token attribute.</param>
/// <param name="smRandom">Random data for set membership proof.</param>
/// <returns>Inequality proof.</returns>
public SetMembershipProof(ProverPresentationProtocolParameters prover, int attributeIndexForProver, byte[][] setValues, SetMembershipProofGenerationRandomData smRandom = null)
{
// generate Pedersen Commitments to token attribute
ProverPresentationProtocolParameters[] provers = new ProverPresentationProtocolParameters[] { prover };
int[] attributeIndices = new int[] { attributeIndexForProver };
PedersenCommitment[] attributeCommitments = PedersenCommitment.PedersenCommmitmentsToAttributes(provers, attributeIndices);
// create set membership proof using Pedersen Commitment
FieldZqElement[] memberSet = VerifierSetMembershipParameters.GenerateMemberSet(prover.IP, attributeIndexForProver, setValues);
ProverSetMembershipParameters setProver = new ProverSetMembershipParameters(attributeCommitments[0], memberSet, new CryptoParameters(prover.IP));
ConstructorHelper(setProver, smRandom);
// add UProve Integration proof
this.UPIProof = new UProveIntegrationProof(provers, attributeIndices, attributeCommitments);
this.UPIProof.IsGroupSerializable = false;
}
} // responses
/// <summary>
/// Constructs a SetMembershipProof. Throws exception if prover
/// parameters do not allow creating valid proof.
/// </summary>
/// <param name="prover">Prover parameters</param>
/// <param name="smRandom">The optional pre-generated random values to generate the proof, or <c>null</c>.</param>
public SetMembershipProof(ProverSetMembershipParameters prover, SetMembershipProofGenerationRandomData smRandom = null)
{
ConstructorHelper(prover, smRandom);
}