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commitment.go
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commitment.go
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// SPDX-License-Identifier: MIT
//
// Copyright (C) 2023 Daniel Bourdrez. All Rights Reserved.
//
// This source code is licensed under the MIT license found in the
// LICENSE file in the root directory of this source tree or at
// https://spdx.org/licenses/MIT.html
package frost
import (
"errors"
"fmt"
"slices"
group "github.com/bytemare/crypto"
"github.com/bytemare/frost/internal"
)
var errDecodeCommitmentLength = errors.New("failed to decode commitment: invalid length")
// Commitment is a participant's one-time commitment holding its identifier, and hiding and binding nonces.
type Commitment struct {
Identifier *group.Scalar
HidingNonce *group.Element
BindingNonce *group.Element
}
// Encode returns the serialized byte encoding of a participant's commitment.
func (c Commitment) Encode() []byte {
id := c.Identifier.Encode()
hNonce := c.HidingNonce.Encode()
bNonce := c.BindingNonce.Encode()
out := make([]byte, len(id)+len(hNonce)+len(bNonce))
copy(out, id)
copy(out[len(id):], hNonce)
copy(out[len(id)+len(hNonce):], bNonce)
return out
}
// DecodeCommitment attempts to deserialize the encoded commitment given as input, and to return it.
func DecodeCommitment(cs Ciphersuite, data []byte) (*Commitment, error) {
g := cs.Configuration().Ciphersuite.Group
scalarLength := g.ScalarLength()
elementLength := g.ElementLength()
if len(data) != scalarLength+2*elementLength {
return nil, errDecodeCommitmentLength
}
c := &Commitment{
Identifier: g.NewScalar(),
HidingNonce: g.NewElement(),
BindingNonce: g.NewElement(),
}
if err := c.Identifier.Decode(data[:scalarLength]); err != nil {
return nil, fmt.Errorf("failed to decode commitment identifier: %w", err)
}
if err := c.HidingNonce.Decode(data[:scalarLength]); err != nil {
return nil, fmt.Errorf("failed to decode commitment hiding nonce: %w", err)
}
if err := c.BindingNonce.Decode(data[:scalarLength]); err != nil {
return nil, fmt.Errorf("failed to decode commitment binding nonce: %w", err)
}
return c, nil
}
// CommitmentList is a sortable list of commitments.
type CommitmentList []*Commitment
func cmpID(a, b *Commitment) int {
switch {
case a.Identifier.Equal(b.Identifier) == 1: // a == b
return 0
case a.Identifier.LessOrEqual(b.Identifier) == 1: // a < b
return -1
default:
return 1
}
}
// Sort sorts the list the ascending order of identifiers.
func (c CommitmentList) Sort() {
slices.SortFunc(c, cmpID)
}
// IsSorted returns whether the list is sorted in ascending order by identifier.
func (c CommitmentList) IsSorted() bool {
return slices.IsSortedFunc(c, cmpID)
}
// Encode serializes a whole commitment list.
func (c CommitmentList) Encode() []byte {
var encoded []byte
for _, l := range c {
e := internal.Concatenate(l.Identifier.Encode(), l.HidingNonce.Encode(), l.BindingNonce.Encode())
encoded = append(encoded, e...)
}
return encoded
}
// Participants returns the list of participants in the commitment list.
func (c CommitmentList) Participants() []*group.Scalar {
identifiers := make([]*group.Scalar, len(c))
for i, l := range c {
identifiers[i] = l.Identifier
}
return identifiers
}
// Get returns the commitment of the participant with the corresponding identifier, or nil if it was not found.
func (c CommitmentList) Get(identifier *group.Scalar) *Commitment {
for _, com := range c {
if com.Identifier.Equal(identifier) == 1 {
return com
}
}
return nil
}