ceremonyclient/nekryptology/pkg/tecdsa/dkls/v0/schnorr.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 v0
import (
"crypto/sha256"
"crypto/subtle"
"fmt"
"math/big"
"source.quilibrium.com/quilibrium/monorepo/nekryptology/pkg/core/curves"
)
type Schnorr struct {
params *Params
Pub *curves.EcPoint // this is the public point.
C *big.Int
S *big.Int
}
func (proof *Schnorr) Prove(x *big.Int) error {
// assumes that params, Base, and pub are already populated. populates the fields c and s...
var err error
proof.Pub, err = curves.NewScalarBaseMult(proof.params.Curve, x) // populate the statement
if err != nil {
return err
}
k, err := proof.params.Scalar.Random()
if err != nil {
return err
}
random, err := curves.NewScalarBaseMult(proof.params.Curve, k)
if err != nil {
return err
}
hash := sha256.New()
if _, err = hash.Write(proof.Pub.Bytes()); err != nil {
return err
}
if _, err = hash.Write(random.Bytes()); err != nil {
return err
}
// do we need to hash anything further here...? maybe some kind of session token or something?
proof.C = new(big.Int).SetBytes(hash.Sum(nil))
proof.S = proof.params.Scalar.Add(proof.params.Scalar.Mul(proof.C, x), k)
return nil
}
func (proof *Schnorr) Verify() error {
gs, err := curves.NewScalarBaseMult(proof.params.Curve, proof.S)
if err != nil {
return err
}
xc, err := proof.Pub.ScalarMult(proof.params.Scalar.Neg(proof.C))
if err != nil {
return err
}
random, err := gs.Add(xc)
if err != nil {
return err
}
hash := sha256.New()
if _, err = hash.Write(proof.Pub.Bytes()); err != nil {
return err
}
if _, err = hash.Write(random.Bytes()); err != nil {
return err
}
if subtle.ConstantTimeCompare(proof.params.Scalar.Bytes(proof.C), hash.Sum(nil)) != 1 {
return fmt.Errorf("Schnorr verification failed")
}
return nil
}
// this "commits to" a schnorr proof which is later revealed; see Functionality 7.
// it mutates `st` by adding a proof to it, and then also returns the commitment to the proof.
func (proof *Schnorr) ProveCommit(x *big.Int) ([]byte, error) {
// it remains to be seen why this is actually necessary in the paper. it's unsual.
// i suspect it is some "abstract nonsense" necessary for the security proof to go through.
// in the implementation (see https://gitlab.com/neucrypt/mpecdsa/-/blob/release/src/zkpok.rs),
// they implement this just by hashing the schnorr proof; we do the same (using c, s as the proof instead of K, s).
// it's a bit weird that no randomness is used, but "hiding" shouldn't really be an issue, as the proof is random.
// confirm that this actually matches how they implement it, and/or is secure. i don't think it should be an issue.
if err := proof.Prove(x); err != nil {
return nil, err
}
hash := sha256.New()
if _, err := hash.Write(proof.params.Scalar.Bytes(proof.C)); err != nil {
return nil, err
}
if _, err := hash.Write(proof.params.Scalar.Bytes(proof.S)); err != nil {
return nil, err
}
return hash.Sum(nil), nil
}
func (proof *Schnorr) DecommitVerify(com []byte) error {
hash := sha256.New()
if _, err := hash.Write(proof.params.Scalar.Bytes(proof.C)); err != nil {
return err
}
if _, err := hash.Write(proof.params.Scalar.Bytes(proof.S)); err != nil {
return err
}
if subtle.ConstantTimeCompare(hash.Sum(nil), com) != 1 {
return fmt.Errorf("initial hash decommitment failed")
}
return proof.Verify()
}