// Verify returns true iff vrf=Compute(m, sk) for the sk that corresponds to pk.
func Verify(pkBytes, m, vrfBytes, proof []byte) bool {
if len(proof) != ProofSize || len(vrfBytes) != Size || len(pkBytes) != PublicKeySize {
return false
}
var pk, c, cRef, t, vrf, iiB, ABytes, BBytes [32]byte
copy(vrf[:], vrfBytes)
copy(pk[:], pkBytes)
copy(c[:32], proof[:32])
copy(t[:32], proof[32:64])
copy(iiB[:], proof[64:96])
hash := sha3.NewShake256()
hash.Write(iiB[:]) // const length
hash.Write(m)
var hCheck [Size]byte
hash.Read(hCheck[:])
if !bytes.Equal(hCheck[:], vrf[:]) {
return false
}
hash.Reset()
var P, B, ii, iic edwards25519.ExtendedGroupElement
var A, hmtP, iicP edwards25519.ProjectiveGroupElement
if !P.FromBytesBaseGroup(&pk) {
return false
}
if !ii.FromBytesBaseGroup(&iiB) {
return false
}
edwards25519.GeDoubleScalarMultVartime(&A, &c, &P, &t)
A.ToBytes(&ABytes)
hm := hashToCurve(m)
edwards25519.GeDoubleScalarMultVartime(&hmtP, &t, hm, &[32]byte{})
edwards25519.GeDoubleScalarMultVartime(&iicP, &c, &ii, &[32]byte{})
iicP.ToExtended(&iic)
hmtP.ToExtended(&B)
edwards25519.GeAdd(&B, &B, &iic)
B.ToBytes(&BBytes)
var cH [64]byte
hash.Write(ABytes[:]) // const length
hash.Write(BBytes[:]) // const length
hash.Write(m)
hash.Read(cH[:])
edwards25519.ScReduce(&cRef, &cH)
return cRef == c
}
// Verify returns true iff sig is a valid signature of message by publicKey.
func Verify(publicKey *[PublicKeySize]byte, message []byte, sig *[SignatureSize]byte) bool {
if sig[63]&224 != 0 {
return false
}
var A edwards25519.ExtendedGroupElement
if !A.FromBytes(publicKey) {
return false
}
edwards25519.FeNeg(&A.X, &A.X)
edwards25519.FeNeg(&A.T, &A.T)
h := sha512.New()
h.Write(sig[:32])
h.Write(publicKey[:])
h.Write(message)
var digest [64]byte
h.Sum(digest[:0])
var hReduced [32]byte
edwards25519.ScReduce(&hReduced, &digest)
var R edwards25519.ProjectiveGroupElement
var b [32]byte
copy(b[:], sig[32:])
edwards25519.GeDoubleScalarMultVartime(&R, &hReduced, &A, &b)
var checkR [32]byte
R.ToBytes(&checkR)
return subtle.ConstantTimeCompare(sig[:32], checkR[:]) == 1
}