1 // Copyright 2016 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
5 // Package ed25519 implements the Ed25519 signature algorithm. See
6 // https://ed25519.cr.yp.to/.
8 // These functions are also compatible with the “Ed25519” function defined in
9 // https://tools.ietf.org/html/draft-irtf-cfrg-eddsa-05.
12 // This code is a port of the public domain, “ref10” implementation of ed25519
17 cryptorand "crypto/rand"
24 "golang.org/x/crypto/ed25519/internal/edwards25519"
28 // PublicKeySize is the size, in bytes, of public keys as used in this package.
30 // PrivateKeySize is the size, in bytes, of private keys as used in this package.
32 // SignatureSize is the size, in bytes, of signatures generated and verified by this package.
36 // PublicKey is the type of Ed25519 public keys.
39 // PrivateKey is the type of Ed25519 private keys. It implements crypto.Signer.
40 type PrivateKey []byte
42 // Public returns the PublicKey corresponding to priv.
43 func (priv PrivateKey) Public() crypto.PublicKey {
44 publicKey := make([]byte, PublicKeySize)
45 copy(publicKey, priv[32:])
46 return PublicKey(publicKey)
49 // Sign signs the given message with priv.
50 // Ed25519 performs two passes over messages to be signed and therefore cannot
51 // handle pre-hashed messages. Thus opts.HashFunc() must return zero to
52 // indicate the message hasn't been hashed. This can be achieved by passing
53 // crypto.Hash(0) as the value for opts.
54 func (priv PrivateKey) Sign(rand io.Reader, message []byte, opts crypto.SignerOpts) (signature []byte, err error) {
55 if opts.HashFunc() != crypto.Hash(0) {
56 return nil, errors.New("ed25519: cannot sign hashed message")
59 return Sign(priv, message), nil
62 // GenerateKey generates a public/private key pair using entropy from rand.
63 // If rand is nil, crypto/rand.Reader will be used.
64 func GenerateKey(rand io.Reader) (publicKey PublicKey, privateKey PrivateKey, err error) {
66 rand = cryptorand.Reader
69 privateKey = make([]byte, PrivateKeySize)
70 publicKey = make([]byte, PublicKeySize)
71 _, err = io.ReadFull(rand, privateKey[:32])
76 digest := sha512.Sum512(privateKey[:32])
81 var A edwards25519.ExtendedGroupElement
83 copy(hBytes[:], digest[:])
84 edwards25519.GeScalarMultBase(&A, &hBytes)
85 var publicKeyBytes [32]byte
86 A.ToBytes(&publicKeyBytes)
88 copy(privateKey[32:], publicKeyBytes[:])
89 copy(publicKey, publicKeyBytes[:])
91 return publicKey, privateKey, nil
94 // Sign signs the message with privateKey and returns a signature. It will
95 // panic if len(privateKey) is not PrivateKeySize.
96 func Sign(privateKey PrivateKey, message []byte) []byte {
97 if l := len(privateKey); l != PrivateKeySize {
98 panic("ed25519: bad private key length: " + strconv.Itoa(l))
102 h.Write(privateKey[:32])
104 var digest1, messageDigest, hramDigest [64]byte
105 var expandedSecretKey [32]byte
107 copy(expandedSecretKey[:], digest1[:])
108 expandedSecretKey[0] &= 248
109 expandedSecretKey[31] &= 63
110 expandedSecretKey[31] |= 64
113 h.Write(digest1[32:])
115 h.Sum(messageDigest[:0])
117 var messageDigestReduced [32]byte
118 edwards25519.ScReduce(&messageDigestReduced, &messageDigest)
119 var R edwards25519.ExtendedGroupElement
120 edwards25519.GeScalarMultBase(&R, &messageDigestReduced)
122 var encodedR [32]byte
127 h.Write(privateKey[32:])
129 h.Sum(hramDigest[:0])
130 var hramDigestReduced [32]byte
131 edwards25519.ScReduce(&hramDigestReduced, &hramDigest)
134 edwards25519.ScMulAdd(&s, &hramDigestReduced, &expandedSecretKey, &messageDigestReduced)
136 signature := make([]byte, SignatureSize)
137 copy(signature[:], encodedR[:])
138 copy(signature[32:], s[:])
143 // Verify reports whether sig is a valid signature of message by publicKey. It
144 // will panic if len(publicKey) is not PublicKeySize.
145 func Verify(publicKey PublicKey, message, sig []byte) bool {
146 if l := len(publicKey); l != PublicKeySize {
147 panic("ed25519: bad public key length: " + strconv.Itoa(l))
150 if len(sig) != SignatureSize || sig[63]&224 != 0 {
154 var A edwards25519.ExtendedGroupElement
155 var publicKeyBytes [32]byte
156 copy(publicKeyBytes[:], publicKey)
157 if !A.FromBytes(&publicKeyBytes) {
160 edwards25519.FeNeg(&A.X, &A.X)
161 edwards25519.FeNeg(&A.T, &A.T)
165 h.Write(publicKey[:])
170 var hReduced [32]byte
171 edwards25519.ScReduce(&hReduced, &digest)
173 var R edwards25519.ProjectiveGroupElement
176 edwards25519.GeDoubleScalarMultVartime(&R, &hReduced, &A, &b)
180 return subtle.ConstantTimeCompare(sig[:32], checkR[:]) == 1