forked from coinbase/kryptology
/
ed25519.go
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/
ed25519.go
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// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package ted25519 implements the Ed25519 signature algorithm. See https://ed25519.cr.yp.to/
//
// These functions are also compatible with the "Ed25519" function defined in
// RFC 8032. However, unlike RFC 8032's formulation, this package's private key
// representation includes a public key suffix to make multiple signing
// operations with the same key more efficient. This package refers to the RFC
// 8032 private key as the "seed".
// This code is a port of the public domain, “ref10” implementation of ed25519
// from SUPERCOP.
package ted25519
import (
"bytes"
"crypto"
cryptorand "crypto/rand"
"crypto/sha512"
"fmt"
"io"
"strconv"
"github.com/berry-block/kryptology/pkg/core/curves"
)
const (
// PublicKeySize is the size, in bytes, of public keys as used in this package.
PublicKeySize = 32
// PrivateKeySize is the size, in bytes, of private keys as used in this package.
PrivateKeySize = 64
// SignatureSize is the size, in bytes, of signatures generated and verified by this package.
SignatureSize = 64
// SeedSize is the size, in bytes, of private key seeds. These are the private key representations used by RFC 8032.
SeedSize = 32
)
// PublicKey is the type of Ed25519 public keys.
type PublicKey []byte
// PrivateKey is the type of Ed25519 private keys. It implements crypto.Signer.
type PrivateKey []byte
// Bytes returns the publicKey in byte array
func (p PublicKey) Bytes() []byte {
return p
}
// Public returns the PublicKey corresponding to priv.
func (priv PrivateKey) Public() crypto.PublicKey {
publicKey := make([]byte, PublicKeySize)
copy(publicKey, priv[32:])
return PublicKey(publicKey)
}
// Seed returns the private key seed corresponding to priv. It is provided for
// interoperability with RFC 8032. RFC 8032's private keys correspond to seeds
// in this package.
func (priv PrivateKey) Seed() []byte {
seed := make([]byte, SeedSize)
copy(seed, priv[:32])
return seed
}
// Sign signs the given message with priv.
// Ed25519 performs two passes over messages to be signed and therefore cannot
// handle pre-hashed messages. Thus opts.HashFunc() must return zero to
// indicate the message hasn't been hashed. This can be achieved by passing
// crypto.Hash(0) as the value for opts.
func (priv PrivateKey) Sign(rand io.Reader, message []byte, opts crypto.SignerOpts) (signature []byte, err error) {
if opts.HashFunc() != crypto.Hash(0) {
return nil, fmt.Errorf("ed25519: cannot sign hashed message")
}
sig, err := Sign(priv, message)
if err != nil {
return nil, err
}
return sig, nil
}
// GenerateKey generates a public/private key pair using entropy from rand.
// If rand is nil, crypto/rand.Reader will be used.
func GenerateKey(rand io.Reader) (PublicKey, PrivateKey, error) {
if rand == nil {
rand = cryptorand.Reader
}
seed := make([]byte, SeedSize)
if _, err := io.ReadFull(rand, seed); err != nil {
return nil, nil, err
}
privateKey, err := NewKeyFromSeed(seed)
if err != nil {
return nil, nil, err
}
publicKey := make([]byte, PublicKeySize)
copy(publicKey, privateKey[32:])
return publicKey, privateKey, nil
}
// NewKeyFromSeed calculates a private key from a seed. It will panic if
// len(seed) is not SeedSize. This function is provided for interoperability
// with RFC 8032. RFC 8032's private keys correspond to seeds in this
// package.
func NewKeyFromSeed(seed []byte) (PrivateKey, error) {
// Outline the function body so that the returned key can be stack-allocated.
privateKey := make([]byte, PrivateKeySize)
err := newKeyFromSeed(privateKey, seed)
if err != nil {
return nil, err
}
return privateKey, nil
}
func newKeyFromSeed(privateKey, seed []byte) error {
if l := len(seed); l != SeedSize {
return fmt.Errorf("ed25519: bad seed length: " + strconv.Itoa(l))
}
digest := sha512.Sum512(seed)
digest[0] &= 248
digest[31] &= 127
digest[31] |= 64
var hBytes [32]byte
copy(hBytes[:], digest[:])
h, err := new(curves.ScalarEd25519).SetBytesClamping(hBytes[:])
if err != nil {
return err
}
ed25519 := curves.ED25519()
A := ed25519.ScalarBaseMult(h)
publicKeyBytes := A.ToAffineCompressed()
copy(privateKey, seed)
copy(privateKey[32:], publicKeyBytes[:])
return nil
}
// Sign signs the message with privateKey and returns a signature. It will
// panic if len(privateKey) is not PrivateKeySize.
func Sign(privateKey PrivateKey, message []byte) ([]byte, error) {
// Outline the function body so that the returned signature can be
// stack-allocated.
signature := make([]byte, SignatureSize)
err := sign(signature, privateKey, message)
if err != nil {
return nil, err
}
return signature, nil
}
func sign(signature, privateKey, message []byte) error {
if l := len(privateKey); l != PrivateKeySize {
return fmt.Errorf("ed25519: bad private key length: " + strconv.Itoa(l))
}
var err error
h := sha512.New()
_, err = h.Write(privateKey[:32])
if err != nil {
return err
}
var digest1, messageDigest, hramDigest [64]byte
var expandedSecretKey [32]byte
_ = h.Sum(digest1[:0])
copy(expandedSecretKey[:], digest1[:])
expandedSecretKey[0] &= 248
expandedSecretKey[31] &= 63
expandedSecretKey[31] |= 64
h.Reset()
_, err = h.Write(digest1[32:])
if err != nil {
return err
}
_, _ = h.Write(message)
if err != nil {
return err
}
_ = h.Sum(messageDigest[:0])
r, err := new(curves.ScalarEd25519).SetBytesWide(messageDigest[:])
if err != nil {
return err
}
// R = r * G
R := curves.ED25519().Point.Generator().Mul(r)
encodedR := R.ToAffineCompressed()
h.Reset()
_, err = h.Write(encodedR[:])
if err != nil {
return err
}
_, err = h.Write(privateKey[32:])
if err != nil {
return err
}
_, err = h.Write(message)
if err != nil {
return err
}
_ = h.Sum(hramDigest[:0])
// Set k and s
k, err := new(curves.ScalarEd25519).SetBytesWide(hramDigest[:])
if err != nil {
return err
}
s, err := new(curves.ScalarEd25519).SetBytesClamping(expandedSecretKey[:])
if err != nil {
return err
}
// S = k*s + r
S := k.MulAdd(s, r)
copy(signature[:], encodedR[:])
copy(signature[32:], S.Bytes()[:])
return nil
}
// Verify reports whether sig is a valid signature of message by publicKey. It
// will panic if len(publicKey) is not PublicKeySize.
// Previously publicKey is of type PublicKey
func Verify(publicKey PublicKey, message, sig []byte) (bool, error) {
if l := len(publicKey); l != PublicKeySize {
return false, fmt.Errorf("ed25519: bad public key length: " + strconv.Itoa(l))
}
if len(sig) != SignatureSize || sig[63]&224 != 0 {
return false, fmt.Errorf("ed25519: bad signature size: " + strconv.Itoa(len(sig)))
}
var publicKeyBytes [32]byte
copy(publicKeyBytes[:], publicKey)
A, err := new(curves.PointEd25519).FromAffineCompressed(publicKeyBytes[:])
if err != nil {
return false, err
}
// Negate sets A = -A, and returns A. It actually negates X and T but keep Y and Z
negA := A.Neg()
h := sha512.New()
_, err = h.Write(sig[:32])
if err != nil {
panic(err)
}
_, err = h.Write(publicKey[:])
if err != nil {
return false, err
}
_, err = h.Write(message)
if err != nil {
return false, err
}
var digest [64]byte
_ = h.Sum(digest[:0])
hReduced, err := new(curves.ScalarEd25519).SetBytesWide(digest[:])
if err != nil {
return false, err
}
var s [32]byte
copy(s[:], sig[32:])
sScalar, err := new(curves.ScalarEd25519).SetBytesCanonical(s[:])
if err != nil {
return false, err
}
// R' = hash * A + s * BasePoint
R := new(curves.PointEd25519).VarTimeDoubleScalarBaseMult(hReduced, negA, sScalar)
// Check R == R'
return bytes.Equal(sig[:32], R.ToAffineCompressed()), nil
}