ed25519.go

Documentation: crypto/ed25519

		 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.
		 4  
		 5  // Package ed25519 implements the Ed25519 signature algorithm. See
		 6  // https://ed25519.cr.yp.to/.
		 7  //
		 8  // These functions are also compatible with the “Ed25519” function defined in
		 9  // RFC 8032. However, unlike RFC 8032's formulation, this package's private key
		10  // representation includes a public key suffix to make multiple signing
		11  // operations with the same key more efficient. This package refers to the RFC
		12  // 8032 private key as the “seed”.
		13  package ed25519
		14  
		15  import (
		16  	"bytes"
		17  	"crypto"
		18  	"crypto/ed25519/internal/edwards25519"
		19  	cryptorand "crypto/rand"
		20  	"crypto/sha512"
		21  	"errors"
		22  	"io"
		23  	"strconv"
		24  )
		25  
		26  const (
		27  	// PublicKeySize is the size, in bytes, of public keys as used in this package.
		28  	PublicKeySize = 32
		29  	// PrivateKeySize is the size, in bytes, of private keys as used in this package.
		30  	PrivateKeySize = 64
		31  	// SignatureSize is the size, in bytes, of signatures generated and verified by this package.
		32  	SignatureSize = 64
		33  	// SeedSize is the size, in bytes, of private key seeds. These are the private key representations used by RFC 8032.
		34  	SeedSize = 32
		35  )
		36  
		37  // PublicKey is the type of Ed25519 public keys.
		38  type PublicKey []byte
		39  
		40  // Any methods implemented on PublicKey might need to also be implemented on
		41  // PrivateKey, as the latter embeds the former and will expose its methods.
		42  
		43  // Equal reports whether pub and x have the same value.
		44  func (pub PublicKey) Equal(x crypto.PublicKey) bool {
		45  	xx, ok := x.(PublicKey)
		46  	if !ok {
		47  		return false
		48  	}
		49  	return bytes.Equal(pub, xx)
		50  }
		51  
		52  // PrivateKey is the type of Ed25519 private keys. It implements crypto.Signer.
		53  type PrivateKey []byte
		54  
		55  // Public returns the PublicKey corresponding to priv.
		56  func (priv PrivateKey) Public() crypto.PublicKey {
		57  	publicKey := make([]byte, PublicKeySize)
		58  	copy(publicKey, priv[32:])
		59  	return PublicKey(publicKey)
		60  }
		61  
		62  // Equal reports whether priv and x have the same value.
		63  func (priv PrivateKey) Equal(x crypto.PrivateKey) bool {
		64  	xx, ok := x.(PrivateKey)
		65  	if !ok {
		66  		return false
		67  	}
		68  	return bytes.Equal(priv, xx)
		69  }
		70  
		71  // Seed returns the private key seed corresponding to priv. It is provided for
		72  // interoperability with RFC 8032. RFC 8032's private keys correspond to seeds
		73  // in this package.
		74  func (priv PrivateKey) Seed() []byte {
		75  	seed := make([]byte, SeedSize)
		76  	copy(seed, priv[:32])
		77  	return seed
		78  }
		79  
		80  // Sign signs the given message with priv.
		81  // Ed25519 performs two passes over messages to be signed and therefore cannot
		82  // handle pre-hashed messages. Thus opts.HashFunc() must return zero to
		83  // indicate the message hasn't been hashed. This can be achieved by passing
		84  // crypto.Hash(0) as the value for opts.
		85  func (priv PrivateKey) Sign(rand io.Reader, message []byte, opts crypto.SignerOpts) (signature []byte, err error) {
		86  	if opts.HashFunc() != crypto.Hash(0) {
		87  		return nil, errors.New("ed25519: cannot sign hashed message")
		88  	}
		89  
		90  	return Sign(priv, message), nil
		91  }
		92  
		93  // GenerateKey generates a public/private key pair using entropy from rand.
		94  // If rand is nil, crypto/rand.Reader will be used.
		95  func GenerateKey(rand io.Reader) (PublicKey, PrivateKey, error) {
		96  	if rand == nil {
		97  		rand = cryptorand.Reader
		98  	}
		99  
	 100  	seed := make([]byte, SeedSize)
	 101  	if _, err := io.ReadFull(rand, seed); err != nil {
	 102  		return nil, nil, err
	 103  	}
	 104  
	 105  	privateKey := NewKeyFromSeed(seed)
	 106  	publicKey := make([]byte, PublicKeySize)
	 107  	copy(publicKey, privateKey[32:])
	 108  
	 109  	return publicKey, privateKey, nil
	 110  }
	 111  
	 112  // NewKeyFromSeed calculates a private key from a seed. It will panic if
	 113  // len(seed) is not SeedSize. This function is provided for interoperability
	 114  // with RFC 8032. RFC 8032's private keys correspond to seeds in this
	 115  // package.
	 116  func NewKeyFromSeed(seed []byte) PrivateKey {
	 117  	// Outline the function body so that the returned key can be stack-allocated.
	 118  	privateKey := make([]byte, PrivateKeySize)
	 119  	newKeyFromSeed(privateKey, seed)
	 120  	return privateKey
	 121  }
	 122  
	 123  func newKeyFromSeed(privateKey, seed []byte) {
	 124  	if l := len(seed); l != SeedSize {
	 125  		panic("ed25519: bad seed length: " + strconv.Itoa(l))
	 126  	}
	 127  
	 128  	h := sha512.Sum512(seed)
	 129  	s := edwards25519.NewScalar().SetBytesWithClamping(h[:32])
	 130  	A := (&edwards25519.Point{}).ScalarBaseMult(s)
	 131  
	 132  	publicKey := A.Bytes()
	 133  
	 134  	copy(privateKey, seed)
	 135  	copy(privateKey[32:], publicKey)
	 136  }
	 137  
	 138  // Sign signs the message with privateKey and returns a signature. It will
	 139  // panic if len(privateKey) is not PrivateKeySize.
	 140  func Sign(privateKey PrivateKey, message []byte) []byte {
	 141  	// Outline the function body so that the returned signature can be
	 142  	// stack-allocated.
	 143  	signature := make([]byte, SignatureSize)
	 144  	sign(signature, privateKey, message)
	 145  	return signature
	 146  }
	 147  
	 148  func sign(signature, privateKey, message []byte) {
	 149  	if l := len(privateKey); l != PrivateKeySize {
	 150  		panic("ed25519: bad private key length: " + strconv.Itoa(l))
	 151  	}
	 152  	seed, publicKey := privateKey[:SeedSize], privateKey[SeedSize:]
	 153  
	 154  	h := sha512.Sum512(seed)
	 155  	s := edwards25519.NewScalar().SetBytesWithClamping(h[:32])
	 156  	prefix := h[32:]
	 157  
	 158  	mh := sha512.New()
	 159  	mh.Write(prefix)
	 160  	mh.Write(message)
	 161  	messageDigest := make([]byte, 0, sha512.Size)
	 162  	messageDigest = mh.Sum(messageDigest)
	 163  	r := edwards25519.NewScalar().SetUniformBytes(messageDigest)
	 164  
	 165  	R := (&edwards25519.Point{}).ScalarBaseMult(r)
	 166  
	 167  	kh := sha512.New()
	 168  	kh.Write(R.Bytes())
	 169  	kh.Write(publicKey)
	 170  	kh.Write(message)
	 171  	hramDigest := make([]byte, 0, sha512.Size)
	 172  	hramDigest = kh.Sum(hramDigest)
	 173  	k := edwards25519.NewScalar().SetUniformBytes(hramDigest)
	 174  
	 175  	S := edwards25519.NewScalar().MultiplyAdd(k, s, r)
	 176  
	 177  	copy(signature[:32], R.Bytes())
	 178  	copy(signature[32:], S.Bytes())
	 179  }
	 180  
	 181  // Verify reports whether sig is a valid signature of message by publicKey. It
	 182  // will panic if len(publicKey) is not PublicKeySize.
	 183  func Verify(publicKey PublicKey, message, sig []byte) bool {
	 184  	if l := len(publicKey); l != PublicKeySize {
	 185  		panic("ed25519: bad public key length: " + strconv.Itoa(l))
	 186  	}
	 187  
	 188  	if len(sig) != SignatureSize || sig[63]&224 != 0 {
	 189  		return false
	 190  	}
	 191  
	 192  	A, err := (&edwards25519.Point{}).SetBytes(publicKey)
	 193  	if err != nil {
	 194  		return false
	 195  	}
	 196  
	 197  	kh := sha512.New()
	 198  	kh.Write(sig[:32])
	 199  	kh.Write(publicKey)
	 200  	kh.Write(message)
	 201  	hramDigest := make([]byte, 0, sha512.Size)
	 202  	hramDigest = kh.Sum(hramDigest)
	 203  	k := edwards25519.NewScalar().SetUniformBytes(hramDigest)
	 204  
	 205  	S, err := edwards25519.NewScalar().SetCanonicalBytes(sig[32:])
	 206  	if err != nil {
	 207  		return false
	 208  	}
	 209  
	 210  	// [S]B = R + [k]A --> [k](-A) + [S]B = R
	 211  	minusA := (&edwards25519.Point{}).Negate(A)
	 212  	R := (&edwards25519.Point{}).VarTimeDoubleScalarBaseMult(k, minusA, S)
	 213  
	 214  	return bytes.Equal(sig[:32], R.Bytes())
	 215  }
	 216
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