ceremonyclient/nekryptology/pkg/signatures/bbs/pok_signature_proof.go

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2023-07-05 05:32:28 +00:00
//
// Copyright Coinbase, Inc. All Rights Reserved.
//
// SPDX-License-Identifier: Apache-2.0
//
package bbs
import (
"errors"
"fmt"
"github.com/gtank/merlin"
"source.quilibrium.com/quilibrium/monorepo/nekryptology/pkg/core/curves"
"source.quilibrium.com/quilibrium/monorepo/nekryptology/pkg/signatures/common"
)
// PokSignatureProof is the actual proof sent from a prover
// to a verifier that contains a proof of knowledge of a signature
// and the selective disclosure proof
type PokSignatureProof struct {
aPrime, aBar, d curves.PairingPoint
proof1, proof2 []curves.Scalar
}
// Init creates an empty proof to a specific curve
// which should be followed by UnmarshalBinary
func (pok *PokSignatureProof) Init(curve *curves.PairingCurve) *PokSignatureProof {
pok.aPrime = curve.Scalar.Point().(curves.PairingPoint).OtherGroup()
pok.aBar = pok.aPrime
pok.d = pok.aPrime
pok.proof1 = []curves.Scalar{
curve.Scalar.Zero(),
curve.Scalar.Zero(),
}
pok.proof2 = make([]curves.Scalar, 0)
return pok
}
func (pok *PokSignatureProof) MarshalBinary() ([]byte, error) {
data := append(pok.aPrime.ToAffineCompressed(), pok.aBar.ToAffineCompressed()...)
data = append(data, pok.d.ToAffineCompressed()...)
for _, p := range pok.proof1 {
data = append(data, p.Bytes()...)
}
for _, p := range pok.proof2 {
data = append(data, p.Bytes()...)
}
return data, nil
}
func (pok *PokSignatureProof) UnmarshalBinary(in []byte) error {
scSize := len(pok.proof1[0].Bytes())
ptSize := len(pok.aPrime.ToAffineCompressed())
minSize := scSize*4 + ptSize*3
inSize := len(in)
if inSize < minSize {
return fmt.Errorf("invalid byte sequence")
}
if (inSize-ptSize)%scSize != 0 {
return fmt.Errorf("invalid byte sequence")
}
secretCnt := ((inSize - ptSize*3) / scSize) - 2
offset := 0
end := ptSize
aPrime, err := pok.aPrime.FromAffineCompressed(in[offset:end])
if err != nil {
return err
}
offset = end
end += ptSize
aBar, err := pok.aBar.FromAffineCompressed(in[offset:end])
if err != nil {
return err
}
offset = end
end += ptSize
d, err := pok.d.FromAffineCompressed(in[offset:end])
if err != nil {
return err
}
offset = end
end += scSize
proof1i0, err := pok.proof1[0].SetBytes(in[offset:end])
if err != nil {
return err
}
offset = end
end += scSize
proof1i1, err := pok.proof1[1].SetBytes(in[offset:end])
if err != nil {
return err
}
proof2 := make([]curves.Scalar, secretCnt)
for i := 0; i < secretCnt; i++ {
offset = end
end += scSize
proof2[i], err = pok.proof1[0].SetBytes(in[offset:end])
if err != nil {
return err
}
}
var ok bool
pok.aPrime, ok = aPrime.(curves.PairingPoint)
if !ok {
return errors.New("incorrect type conversion")
}
pok.aBar, ok = aBar.(curves.PairingPoint)
if !ok {
return errors.New("incorrect type conversion")
}
pok.d, ok = d.(curves.PairingPoint)
if !ok {
return errors.New("incorrect type conversion")
}
pok.proof1[0] = proof1i0
pok.proof1[1] = proof1i1
pok.proof2 = proof2
return nil
}
// GetChallengeContribution converts the committed values to bytes
// for the Fiat-Shamir challenge
func (pok PokSignatureProof) GetChallengeContribution(
generators *MessageGenerators,
revealedMessages map[int]curves.Scalar,
challenge common.Challenge,
transcript *merlin.Transcript,
) {
transcript.AppendMessage([]byte("A'"), pok.aPrime.ToAffineCompressed())
transcript.AppendMessage([]byte("Abar"), pok.aBar.ToAffineCompressed())
transcript.AppendMessage([]byte("D"), pok.d.ToAffineCompressed())
proof1Points := []curves.Point{pok.aBar.Sub(pok.d), pok.aPrime, generators.h0}
proof1Scalars := []curves.Scalar{challenge, pok.proof1[0], pok.proof1[1]}
commitmentProof1 := pok.aPrime.SumOfProducts(proof1Points, proof1Scalars)
transcript.AppendMessage([]byte("Proof1"), commitmentProof1.ToAffineCompressed())
rPoints := make([]curves.Point, 1, len(revealedMessages)+1)
rScalars := make([]curves.Scalar, 1, len(revealedMessages)+1)
rPoints[0] = pok.aPrime.Generator()
rScalars[0] = pok.proof1[0].One()
for idx, msg := range revealedMessages {
rPoints = append(rPoints, generators.Get(idx+1))
rScalars = append(rScalars, msg)
}
r := pok.aPrime.SumOfProducts(rPoints, rScalars)
pts := 3 + generators.length - len(revealedMessages)
proof2Points := make([]curves.Point, 3, pts)
proof2Scalars := make([]curves.Scalar, 3, pts)
// R * c
proof2Points[0] = r
proof2Scalars[0] = challenge
// D * -r3Hat
proof2Points[1] = pok.d.Neg()
proof2Scalars[1] = pok.proof2[0]
// H0 * s'Hat
proof2Points[2] = generators.h0
proof2Scalars[2] = pok.proof2[1]
j := 2
for i := 0; i < generators.length; i++ {
if _, contains := revealedMessages[i]; contains {
continue
}
proof2Points = append(proof2Points, generators.Get(i+1))
proof2Scalars = append(proof2Scalars, pok.proof2[j])
j++
}
commitmentProof2 := r.SumOfProducts(proof2Points, proof2Scalars)
transcript.AppendMessage([]byte("Proof2"), commitmentProof2.ToAffineCompressed())
}
// VerifySigPok only validates the signature proof,
// the selective disclosure proof is checked by
// verifying
// pok.challenge == computedChallenge
func (pok PokSignatureProof) VerifySigPok(pk *PublicKey) bool {
return !pk.value.IsIdentity() &&
!pok.aPrime.IsIdentity() &&
!pok.aBar.IsIdentity() &&
pok.aPrime.MultiPairing(pok.aPrime, pk.value, pok.aBar, pk.value.Generator().Neg().(curves.PairingPoint)).IsOne()
}
// Verify checks a signature proof of knowledge and selective disclosure proof
func (pok PokSignatureProof) Verify(
revealedMsgs map[int]curves.Scalar,
pk *PublicKey,
generators *MessageGenerators,
nonce common.Nonce,
challenge common.Challenge,
transcript *merlin.Transcript,
) bool {
pok.GetChallengeContribution(generators, revealedMsgs, challenge, transcript)
transcript.AppendMessage([]byte("nonce"), nonce.Bytes())
okm := transcript.ExtractBytes([]byte("signature proof of knowledge"), 64)
vChallenge, err := pok.proof1[0].SetBytesWide(okm)
if err != nil {
return false
}
return pok.VerifySigPok(pk) && challenge.Cmp(vChallenge) == 0
}