224 lines
6.5 KiB
Go
224 lines
6.5 KiB
Go
// Copyright 2016 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// In Go 1.13, the ed25519 package was promoted to the standard library as
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// crypto/ed25519, and this package became a wrapper for the standard library one.
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//
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//go:build !go1.13
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// +build !go1.13
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// Package ed25519 implements the Ed25519 signature algorithm. See
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// https://ed25519.cr.yp.to/.
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//
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// These functions are also compatible with the “Ed25519” function defined in
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// RFC 8032. However, unlike RFC 8032's formulation, this package's private key
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// representation includes a public key suffix to make multiple signing
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// operations with the same key more efficient. This package refers to the RFC
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// 8032 private key as the “seed”.
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package ed25519
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// This code is a port of the public domain, “ref10” implementation of ed25519
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// from SUPERCOP.
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import (
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"bytes"
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"crypto"
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cryptorand "crypto/rand"
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"crypto/sha512"
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"errors"
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"io"
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"strconv"
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"golang.org/x/crypto/ed25519/internal/edwards25519"
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)
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const (
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// PublicKeySize is the size, in bytes, of public keys as used in this package.
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PublicKeySize = 32
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// PrivateKeySize is the size, in bytes, of private keys as used in this package.
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PrivateKeySize = 64
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// SignatureSize is the size, in bytes, of signatures generated and verified by this package.
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SignatureSize = 64
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// SeedSize is the size, in bytes, of private key seeds. These are the private key representations used by RFC 8032.
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SeedSize = 32
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)
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// PublicKey is the type of Ed25519 public keys.
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type PublicKey []byte
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// PrivateKey is the type of Ed25519 private keys. It implements crypto.Signer.
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type PrivateKey []byte
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// Public returns the PublicKey corresponding to priv.
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func (priv PrivateKey) Public() crypto.PublicKey {
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publicKey := make([]byte, PublicKeySize)
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copy(publicKey, priv[32:])
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return PublicKey(publicKey)
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}
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// Seed returns the private key seed corresponding to priv. It is provided for
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// interoperability with RFC 8032. RFC 8032's private keys correspond to seeds
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// in this package.
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func (priv PrivateKey) Seed() []byte {
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seed := make([]byte, SeedSize)
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copy(seed, priv[:32])
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return seed
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}
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// Sign signs the given message with priv.
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// Ed25519 performs two passes over messages to be signed and therefore cannot
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// handle pre-hashed messages. Thus opts.HashFunc() must return zero to
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// indicate the message hasn't been hashed. This can be achieved by passing
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// crypto.Hash(0) as the value for opts.
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func (priv PrivateKey) Sign(rand io.Reader, message []byte, opts crypto.SignerOpts) (signature []byte, err error) {
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if opts.HashFunc() != crypto.Hash(0) {
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return nil, errors.New("ed25519: cannot sign hashed message")
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}
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return Sign(priv, message), nil
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}
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// GenerateKey generates a public/private key pair using entropy from rand.
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// If rand is nil, crypto/rand.Reader will be used.
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func GenerateKey(rand io.Reader) (PublicKey, PrivateKey, error) {
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if rand == nil {
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rand = cryptorand.Reader
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}
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seed := make([]byte, SeedSize)
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if _, err := io.ReadFull(rand, seed); err != nil {
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return nil, nil, err
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}
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privateKey := NewKeyFromSeed(seed)
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publicKey := make([]byte, PublicKeySize)
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copy(publicKey, privateKey[32:])
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return publicKey, privateKey, nil
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}
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// NewKeyFromSeed calculates a private key from a seed. It will panic if
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// len(seed) is not SeedSize. This function is provided for interoperability
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// with RFC 8032. RFC 8032's private keys correspond to seeds in this
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// package.
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func NewKeyFromSeed(seed []byte) PrivateKey {
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if l := len(seed); l != SeedSize {
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panic("ed25519: bad seed length: " + strconv.Itoa(l))
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}
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digest := sha512.Sum512(seed)
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digest[0] &= 248
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digest[31] &= 127
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digest[31] |= 64
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var A edwards25519.ExtendedGroupElement
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var hBytes [32]byte
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copy(hBytes[:], digest[:])
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edwards25519.GeScalarMultBase(&A, &hBytes)
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var publicKeyBytes [32]byte
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A.ToBytes(&publicKeyBytes)
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privateKey := make([]byte, PrivateKeySize)
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copy(privateKey, seed)
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copy(privateKey[32:], publicKeyBytes[:])
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return privateKey
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}
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// Sign signs the message with privateKey and returns a signature. It will
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// panic if len(privateKey) is not PrivateKeySize.
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func Sign(privateKey PrivateKey, message []byte) []byte {
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if l := len(privateKey); l != PrivateKeySize {
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panic("ed25519: bad private key length: " + strconv.Itoa(l))
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}
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h := sha512.New()
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h.Write(privateKey[:32])
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var digest1, messageDigest, hramDigest [64]byte
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var expandedSecretKey [32]byte
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h.Sum(digest1[:0])
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copy(expandedSecretKey[:], digest1[:])
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expandedSecretKey[0] &= 248
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expandedSecretKey[31] &= 63
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expandedSecretKey[31] |= 64
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h.Reset()
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h.Write(digest1[32:])
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h.Write(message)
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h.Sum(messageDigest[:0])
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var messageDigestReduced [32]byte
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edwards25519.ScReduce(&messageDigestReduced, &messageDigest)
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var R edwards25519.ExtendedGroupElement
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edwards25519.GeScalarMultBase(&R, &messageDigestReduced)
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var encodedR [32]byte
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R.ToBytes(&encodedR)
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h.Reset()
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h.Write(encodedR[:])
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h.Write(privateKey[32:])
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h.Write(message)
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h.Sum(hramDigest[:0])
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var hramDigestReduced [32]byte
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edwards25519.ScReduce(&hramDigestReduced, &hramDigest)
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var s [32]byte
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edwards25519.ScMulAdd(&s, &hramDigestReduced, &expandedSecretKey, &messageDigestReduced)
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signature := make([]byte, SignatureSize)
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copy(signature[:], encodedR[:])
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copy(signature[32:], s[:])
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return signature
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}
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// Verify reports whether sig is a valid signature of message by publicKey. It
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// will panic if len(publicKey) is not PublicKeySize.
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func Verify(publicKey PublicKey, message, sig []byte) bool {
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if l := len(publicKey); l != PublicKeySize {
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panic("ed25519: bad public key length: " + strconv.Itoa(l))
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}
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if len(sig) != SignatureSize || sig[63]&224 != 0 {
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return false
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}
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var A edwards25519.ExtendedGroupElement
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var publicKeyBytes [32]byte
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copy(publicKeyBytes[:], publicKey)
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if !A.FromBytes(&publicKeyBytes) {
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return false
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}
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edwards25519.FeNeg(&A.X, &A.X)
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edwards25519.FeNeg(&A.T, &A.T)
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h := sha512.New()
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h.Write(sig[:32])
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h.Write(publicKey[:])
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h.Write(message)
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var digest [64]byte
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h.Sum(digest[:0])
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var hReduced [32]byte
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edwards25519.ScReduce(&hReduced, &digest)
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var R edwards25519.ProjectiveGroupElement
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var s [32]byte
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copy(s[:], sig[32:])
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// https://tools.ietf.org/html/rfc8032#section-5.1.7 requires that s be in
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// the range [0, order) in order to prevent signature malleability.
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if !edwards25519.ScMinimal(&s) {
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return false
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}
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edwards25519.GeDoubleScalarMultVartime(&R, &hReduced, &A, &s)
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var checkR [32]byte
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R.ToBytes(&checkR)
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return bytes.Equal(sig[:32], checkR[:])
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}
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