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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 ed25519 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”.
package ed25519
import (
"bytes"
"crypto"
"crypto/ed25519/internal/edwards25519"
cryptorand "crypto/rand"
"crypto/sha512"
"errors"
"io"
"strconv"
)
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
// Any methods implemented on PublicKey might need to also be implemented on
// PrivateKey, as the latter embeds the former and will expose its methods.
// Equal reports whether pub and x have the same value.
func (pub PublicKey) Equal(x crypto.PublicKey) bool {
xx, ok := x.(PublicKey)
if !ok {
return false
}
return bytes.Equal(pub, xx)
}
// PrivateKey is the type of Ed25519 private keys. It implements crypto.Signer.
type PrivateKey []byte
// Public returns the PublicKey corresponding to priv.
func (priv PrivateKey) Public() crypto.PublicKey {
publicKey := make([]byte, PublicKeySize)
copy(publicKey, priv[32:])
return PublicKey(publicKey)
}
// Equal reports whether priv and x have the same value.
func (priv PrivateKey) Equal(x crypto.PrivateKey) bool {
xx, ok := x.(PrivateKey)
if !ok {
return false
}
return bytes.Equal(priv, xx)
}
// 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, errors.New("ed25519: cannot sign hashed message")
}
return Sign(priv, message), 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 := NewKeyFromSeed(seed)
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 {
// Outline the function body so that the returned key can be stack-allocated.
privateKey := make([]byte, PrivateKeySize)
newKeyFromSeed(privateKey, seed)
return privateKey
}
func newKeyFromSeed(privateKey, seed []byte) {
if l := len(seed); l != SeedSize {
panic("ed25519: bad seed length: " + strconv.Itoa(l))
}
h := sha512.Sum512(seed)
s := edwards25519.NewScalar().SetBytesWithClamping(h[:32])
A := (&edwards25519.Point{}).ScalarBaseMult(s)
publicKey := A.Bytes()
copy(privateKey, seed)
copy(privateKey[32:], publicKey)
}
// 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 {
// Outline the function body so that the returned signature can be
// stack-allocated.
signature := make([]byte, SignatureSize)
sign(signature, privateKey, message)
return signature
}
func sign(signature, privateKey, message []byte) {
if l := len(privateKey); l != PrivateKeySize {
panic("ed25519: bad private key length: " + strconv.Itoa(l))
}
seed, publicKey := privateKey[:SeedSize], privateKey[SeedSize:]
h := sha512.Sum512(seed)
s := edwards25519.NewScalar().SetBytesWithClamping(h[:32])
prefix := h[32:]
mh := sha512.New()
mh.Write(prefix)
mh.Write(message)
messageDigest := make([]byte, 0, sha512.Size)
messageDigest = mh.Sum(messageDigest)
r := edwards25519.NewScalar().SetUniformBytes(messageDigest)
R := (&edwards25519.Point{}).ScalarBaseMult(r)
kh := sha512.New()
kh.Write(R.Bytes())
kh.Write(publicKey)
kh.Write(message)
hramDigest := make([]byte, 0, sha512.Size)
hramDigest = kh.Sum(hramDigest)
k := edwards25519.NewScalar().SetUniformBytes(hramDigest)
S := edwards25519.NewScalar().MultiplyAdd(k, s, r)
copy(signature[:32], R.Bytes())
copy(signature[32:], S.Bytes())
}
// Verify reports whether sig is a valid signature of message by publicKey. It
// will panic if len(publicKey) is not PublicKeySize.
func Verify(publicKey PublicKey, message, sig []byte) bool {
if l := len(publicKey); l != PublicKeySize {
panic("ed25519: bad public key length: " + strconv.Itoa(l))
}
if len(sig) != SignatureSize || sig[63]&224 != 0 {
return false
}
A, err := (&edwards25519.Point{}).SetBytes(publicKey)
if err != nil {
return false
}
kh := sha512.New()
kh.Write(sig[:32])
kh.Write(publicKey)
kh.Write(message)
hramDigest := make([]byte, 0, sha512.Size)
hramDigest = kh.Sum(hramDigest)
k := edwards25519.NewScalar().SetUniformBytes(hramDigest)
S, err := edwards25519.NewScalar().SetCanonicalBytes(sig[32:])
if err != nil {
return false
}
// [S]B = R + [k]A --> [k](-A) + [S]B = R
minusA := (&edwards25519.Point{}).Negate(A)
R := (&edwards25519.Point{}).VarTimeDoubleScalarBaseMult(k, minusA, S)
return bytes.Equal(sig[:32], R.Bytes())
}
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