/**
* Create a new IdemixSignature by proving knowledge of a credential
*
* @param c the credential used to create an idemix signature
* @param sk the signer's secret key
* @param pseudonym a pseudonym of the signer
* @param ipk the issuer public key
* @param disclosure a bool-array that steers the disclosure of attributes
* @param msg the message to be signed
* @param rhIndex the index of the attribute that represents the revocation handle
* @param cri the credential revocation information that allows the signer to prove non-revocation
*/
public IdemixSignature(IdemixCredential c, BIG sk, IdemixPseudonym pseudonym, IdemixIssuerPublicKey ipk, bool[] disclosure, byte[] msg, int rhIndex, CredentialRevocationInformation cri)
{
if (c == null || sk == null || pseudonym == null || pseudonym.Nym == null || pseudonym.RandNym == null || ipk == null || disclosure == null || msg == null || cri == null)
{
throw new ArgumentException("Cannot construct idemix signature from null input");
}
if (disclosure.Length != c.Attrs.Length)
{
throw new ArgumentException("Disclosure length must be the same as the number of attributes");
}
if (cri.RevocationAlg >= Enum.GetValues(typeof(RevocationAlgorithm)).Length)
{
throw new ArgumentException("CRI specifies unknown revocation algorithm");
}
if (cri.RevocationAlg != (int)RevocationAlgorithm.ALG_NO_REVOCATION && disclosure[rhIndex])
{
throw new ArgumentException("Attribute " + rhIndex + " is disclosed but also used a revocation handle attribute, which should remain hidden");
}
RevocationAlgorithm revocationAlgorithm = (RevocationAlgorithm)cri.RevocationAlg;
int[] hiddenIndices = HiddenIndices(disclosure);
RAND rng = IdemixUtils.GetRand();
// Start signature
BIG r1 = rng.RandModOrder();
BIG r2 = rng.RandModOrder();
BIG r3 = new BIG(r1);
r3.InvModp(IdemixUtils.GROUP_ORDER);
nonce = rng.RandModOrder();
aPrime = PAIR.G1Mul(c.A, r1);
aBar = PAIR.G1Mul(c.B, r1);
aBar.Sub(PAIR.G1Mul(aPrime, c.E));
bPrime = PAIR.G1Mul(c.B, r1);
bPrime.Sub(PAIR.G1Mul(ipk.HRand, r2));
BIG sPrime = new BIG(c.S);
sPrime.Add(BIG.ModNeg(BIG.ModMul(r2, r3, IdemixUtils.GROUP_ORDER), IdemixUtils.GROUP_ORDER));
sPrime.Mod(IdemixUtils.GROUP_ORDER);
//Construct Zero Knowledge Proof
BIG rsk = rng.RandModOrder();
BIG re = rng.RandModOrder();
BIG rR2 = rng.RandModOrder();
BIG rR3 = rng.RandModOrder();
BIG rSPrime = rng.RandModOrder();
BIG rRNym = rng.RandModOrder();
BIG[] rAttrs = new BIG[hiddenIndices.Length];
for (int i = 0; i < hiddenIndices.Length; i++)
{
rAttrs[i] = rng.RandModOrder();
}
// Compute non-revoked proof
INonRevocationProver prover = NonRevocationProver.GetNonRevocationProver(revocationAlgorithm);
int hiddenRHIndex = Array.IndexOf(hiddenIndices, rhIndex);
if (hiddenRHIndex < 0)
{
// rhIndex is not present, set to last index position
hiddenRHIndex = hiddenIndices.Length;
}
byte[] nonRevokedProofHashData = prover.GetFSContribution(BIG.FromBytes(c.Attrs[rhIndex]), rAttrs[hiddenRHIndex], cri);
if (nonRevokedProofHashData == null)
{
throw new Exception("Failed to compute non-revoked proof");
}
ECP t1 = aPrime.Mul2(re, ipk.HRand, rR2);
ECP t2 = PAIR.G1Mul(ipk.HRand, rSPrime);
t2.Add(bPrime.Mul2(rR3, ipk.Hsk, rsk));
for (int i = 0; i < hiddenIndices.Length / 2; i++)
{
t2.Add(ipk.HAttrs[hiddenIndices[2 * i]].Mul2(rAttrs[2 * i], ipk.HAttrs[hiddenIndices[2 * i + 1]], rAttrs[2 * i + 1]));
}
if (hiddenIndices.Length % 2 != 0)
{
t2.Add(PAIR.G1Mul(ipk.HAttrs[hiddenIndices[hiddenIndices.Length - 1]], rAttrs[hiddenIndices.Length - 1]));
}
ECP t3 = ipk.Hsk.Mul2(rsk, ipk.HRand, rRNym);
// create proofData such that it can contain the sign label, 7 elements in G1 (each of size 2*FIELD_BYTES+1),
// the ipk hash, the disclosure array, and the message
byte[] proofData = new byte[0];
proofData = proofData.Append(SIGN_LABEL.ToBytes());
proofData = proofData.Append(t1.ToBytes());
proofData = proofData.Append(t2.ToBytes());
proofData = proofData.Append(t3.ToBytes());
proofData = proofData.Append(aPrime.ToBytes());
proofData = proofData.Append(aBar.ToBytes());
proofData = proofData.Append(bPrime.ToBytes());
proofData = proofData.Append(pseudonym.Nym.ToBytes());
proofData = proofData.Append(ipk.Hash);
proofData = proofData.Append(disclosure);
proofData = proofData.Append(msg);
BIG cvalue = proofData.HashModOrder();
byte[] finalProofData = new byte[0];
finalProofData = finalProofData.Append(cvalue.ToBytes());
finalProofData = finalProofData.Append(nonce.ToBytes());
proofC = finalProofData.HashModOrder();
proofSSk = rsk.ModAdd(BIG.ModMul(proofC, sk, IdemixUtils.GROUP_ORDER), IdemixUtils.GROUP_ORDER);
proofSE = re.ModSub(BIG.ModMul(proofC, c.E, IdemixUtils.GROUP_ORDER), IdemixUtils.GROUP_ORDER);
proofSR2 = rR2.ModAdd(BIG.ModMul(proofC, r2, IdemixUtils.GROUP_ORDER), IdemixUtils.GROUP_ORDER);
proofSR3 = rR3.ModSub(BIG.ModMul(proofC, r3, IdemixUtils.GROUP_ORDER), IdemixUtils.GROUP_ORDER);
proofSSPrime = rSPrime.ModAdd(BIG.ModMul(proofC, sPrime, IdemixUtils.GROUP_ORDER), IdemixUtils.GROUP_ORDER);
proofSRNym = rRNym.ModAdd(BIG.ModMul(proofC, pseudonym.RandNym, IdemixUtils.GROUP_ORDER), IdemixUtils.GROUP_ORDER);
nym = new ECP();
nym.Copy(pseudonym.Nym);
proofSAttrs = new BIG[hiddenIndices.Length];
for (int i = 0; i < hiddenIndices.Length; i++)
{
proofSAttrs[i] = new BIG(rAttrs[i]);
proofSAttrs[i].Add(BIG.ModMul(proofC, BIG.FromBytes(c.Attrs[hiddenIndices[i]]), IdemixUtils.GROUP_ORDER));
proofSAttrs[i].Mod(IdemixUtils.GROUP_ORDER);
}
// include non-revocation proof in signature
revocationPk = cri.EpochPk;
revocationPKSig = cri.EpochPkSig.ToByteArray();
epoch = cri.Epoch;
nonRevocationProof = prover.GetNonRevocationProof(proofC);
}
/**
* Verify this signature
*
* @param disclosure an array indicating which attributes it expects to be disclosed
* @param ipk the issuer public key
* @param msg the message that should be signed in this signature
* @param attributeValues BIG array where attributeValues[i] contains the desired attribute value for the i-th attribute if its disclosed
* @param rhIndex index of the attribute that represents the revocation-handle
* @param revPk the long term public key used to authenticate CRIs
* @param epoch monotonically increasing counter representing a time window
* @return true iff valid
*/
// ReSharper disable once ParameterHidesMember
public bool Verify(bool[] disclosure, IdemixIssuerPublicKey ipk, byte[] msg, BIG[] attributeValues, int rhIndex, KeyPair revPk, int epoch)
{
if (disclosure == null || ipk == null || msg == null || attributeValues == null || attributeValues.Length != ipk.AttributeNames.Length || disclosure.Length != ipk.AttributeNames.Length)
{
return(false);
}
for (int i = 0; i < ipk.AttributeNames.Length; i++)
{
if (disclosure[i] && attributeValues[i] == null)
{
return(false);
}
}
int[] hiddenIndices = HiddenIndices(disclosure);
if (proofSAttrs.Length != hiddenIndices.Length)
{
return(false);
}
if (aPrime.IsInfinity())
{
return(false);
}
if (nonRevocationProof.RevocationAlg >= Enum.GetValues(typeof(RevocationAlgorithm)).Length)
{
throw new ArgumentException("CRI specifies unknown revocation algorithm");
}
RevocationAlgorithm revocationAlgorithm = (RevocationAlgorithm)nonRevocationProof.RevocationAlg;
if (disclosure[rhIndex])
{
throw new ArgumentException("Attribute " + rhIndex + " is disclosed but also used a revocation handle attribute, which should remain hidden");
}
// Verify EpochPK
if (!RevocationAuthority.VerifyEpochPK(revPk, revocationPk, revocationPKSig, epoch, revocationAlgorithm))
{
// Signature is based on an invalid revocation epoch public key
return(false);
}
FP12 temp1 = PAIR.Ate(ipk.W, aPrime);
FP12 temp2 = PAIR.Ate(IdemixUtils.GenG2, aBar);
temp2.Inverse();
temp1.mul(temp2);
if (!PAIR.FExp(temp1).IsUnity())
{
return(false);
}
ECP t1 = aPrime.Mul2(proofSE, ipk.HRand, proofSR2);
ECP temp = new ECP();
temp.Copy(aBar);
temp.Sub(bPrime);
t1.Sub(PAIR.G1Mul(temp, proofC));
ECP t2 = PAIR.G1Mul(ipk.HRand, proofSSPrime);
t2.Add(bPrime.Mul2(proofSR3, ipk.Hsk, proofSSk));
for (int i = 0; i < hiddenIndices.Length / 2; i++)
{
t2.Add(ipk.HAttrs[hiddenIndices[2 * i]].Mul2(proofSAttrs[2 * i], ipk.HAttrs[hiddenIndices[2 * i + 1]], proofSAttrs[2 * i + 1]));
}
if (hiddenIndices.Length % 2 != 0)
{
t2.Add(PAIR.G1Mul(ipk.HAttrs[hiddenIndices[hiddenIndices.Length - 1]], proofSAttrs[hiddenIndices.Length - 1]));
}
temp = new ECP();
temp.Copy(IdemixUtils.GenG1);
for (int i = 0; i < disclosure.Length; i++)
{
if (disclosure[i])
{
temp.Add(PAIR.G1Mul(ipk.HAttrs[i], attributeValues[i]));
}
}
t2.Add(PAIR.G1Mul(temp, proofC));
ECP t3 = ipk.Hsk.Mul2(proofSSk, ipk.HRand, proofSRNym);
t3.Sub(nym.Mul(proofC));
// Check with non-revoked-verifier
INonRevocationVerifier nonRevokedVerifier = NonRevocationVerifier.GetNonRevocationVerifier(revocationAlgorithm);
int hiddenRHIndex = Array.IndexOf(hiddenIndices, rhIndex);
if (hiddenRHIndex < 0)
{
// rhIndex is not present, set to last index position
hiddenRHIndex = hiddenIndices.Length;
}
BIG proofSRh = proofSAttrs[hiddenRHIndex];
byte[] nonRevokedProofBytes = nonRevokedVerifier.RecomputeFSContribution(nonRevocationProof, proofC, revocationPk.ToECP2(), proofSRh);
if (nonRevokedProofBytes == null)
{
return(false);
}
// create proofData such that it can contain the sign label, 7 elements in G1 (each of size 2*FIELD_BYTES+1),
// the ipk hash, the disclosure array, and the message
byte[] proofData = new byte[0];
proofData = proofData.Append(SIGN_LABEL.ToBytes());
proofData = proofData.Append(t1.ToBytes());
proofData = proofData.Append(t2.ToBytes());
proofData = proofData.Append(t3.ToBytes());
proofData = proofData.Append(aPrime.ToBytes());
proofData = proofData.Append(aBar.ToBytes());
proofData = proofData.Append(bPrime.ToBytes());
proofData = proofData.Append(nym.ToBytes());
proofData = proofData.Append(ipk.Hash);
proofData = proofData.Append(disclosure);
proofData = proofData.Append(msg);
BIG cvalue = proofData.HashModOrder();
byte[] finalProofData = new byte[0];
finalProofData = finalProofData.Append(cvalue.ToBytes());
finalProofData = finalProofData.Append(nonce.ToBytes());
byte[] hashedProofData = finalProofData.HashModOrder().ToBytes();
return(Enumerable.SequenceEqual(proofC.ToBytes(), hashedProofData));
}