ed25519.go

     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  // In Go 1.13, the ed25519 package was promoted to the standard library as
     6  // crypto/ed25519, and this package became a wrapper for the standard library one.
     7  //
     8  //go:build !go1.13
     9  // +build !go1.13
    10  
    11  // Package ed25519 implements the Ed25519 signature algorithm. See
    12  // https://ed25519.cr.yp.to/.
    13  //
    14  // These functions are also compatible with the “Ed25519” function defined in
    15  // RFC 8032. However, unlike RFC 8032's formulation, this package's private key
    16  // representation includes a public key suffix to make multiple signing
    17  // operations with the same key more efficient. This package refers to the RFC
    18  // 8032 private key as the “seed”.
    19  package ed25519
    20  
    21  // This code is a port of the public domain, “ref10” implementation of ed25519
    22  // from SUPERCOP.
    23  
    24  import (
    25  	"bytes"
    26  	"crypto"
    27  	cryptorand "crypto/rand"
    28  	"crypto/sha512"
    29  	"errors"
    30  	"io"
    31  	"strconv"
    32  
    33  	"golang.org/x/crypto/ed25519/internal/edwards25519"
    34  )
    35  
    36  const (
    37  	// PublicKeySize is the size, in bytes, of public keys as used in this package.
    38  	PublicKeySize = 32
    39  	// PrivateKeySize is the size, in bytes, of private keys as used in this package.
    40  	PrivateKeySize = 64
    41  	// SignatureSize is the size, in bytes, of signatures generated and verified by this package.
    42  	SignatureSize = 64
    43  	// SeedSize is the size, in bytes, of private key seeds. These are the private key representations used by RFC 8032.
    44  	SeedSize = 32
    45  )
    46  
    47  // PublicKey is the type of Ed25519 public keys.
    48  type PublicKey []byte
    49  
    50  // PrivateKey is the type of Ed25519 private keys. It implements crypto.Signer.
    51  type PrivateKey []byte
    52  
    53  // Public returns the PublicKey corresponding to priv.
    54  func (priv PrivateKey) Public() crypto.PublicKey {
    55  	publicKey := make([]byte, PublicKeySize)
    56  	copy(publicKey, priv[32:])
    57  	return PublicKey(publicKey)
    58  }
    59  
    60  // Seed returns the private key seed corresponding to priv. It is provided for
    61  // interoperability with RFC 8032. RFC 8032's private keys correspond to seeds
    62  // in this package.
    63  func (priv PrivateKey) Seed() []byte {
    64  	seed := make([]byte, SeedSize)
    65  	copy(seed, priv[:32])
    66  	return seed
    67  }
    68  
    69  // Sign signs the given message with priv.
    70  // Ed25519 performs two passes over messages to be signed and therefore cannot
    71  // handle pre-hashed messages. Thus opts.HashFunc() must return zero to
    72  // indicate the message hasn't been hashed. This can be achieved by passing
    73  // crypto.Hash(0) as the value for opts.
    74  func (priv PrivateKey) Sign(rand io.Reader, message []byte, opts crypto.SignerOpts) (signature []byte, err error) {
    75  	if opts.HashFunc() != crypto.Hash(0) {
    76  		return nil, errors.New("ed25519: cannot sign hashed message")
    77  	}
    78  
    79  	return Sign(priv, message), nil
    80  }
    81  
    82  // GenerateKey generates a public/private key pair using entropy from rand.
    83  // If rand is nil, crypto/rand.Reader will be used.
    84  func GenerateKey(rand io.Reader) (PublicKey, PrivateKey, error) {
    85  	if rand == nil {
    86  		rand = cryptorand.Reader
    87  	}
    88  
    89  	seed := make([]byte, SeedSize)
    90  	if _, err := io.ReadFull(rand, seed); err != nil {
    91  		return nil, nil, err
    92  	}
    93  
    94  	privateKey := NewKeyFromSeed(seed)
    95  	publicKey := make([]byte, PublicKeySize)
    96  	copy(publicKey, privateKey[32:])
    97  
    98  	return publicKey, privateKey, nil
    99  }
   100  
   101  // NewKeyFromSeed calculates a private key from a seed. It will panic if
   102  // len(seed) is not SeedSize. This function is provided for interoperability
   103  // with RFC 8032. RFC 8032's private keys correspond to seeds in this
   104  // package.
   105  func NewKeyFromSeed(seed []byte) PrivateKey {
   106  	if l := len(seed); l != SeedSize {
   107  		panic("ed25519: bad seed length: " + strconv.Itoa(l))
   108  	}
   109  
   110  	digest := sha512.Sum512(seed)
   111  	digest[0] &= 248
   112  	digest[31] &= 127
   113  	digest[31] |= 64
   114  
   115  	var A edwards25519.ExtendedGroupElement
   116  	var hBytes [32]byte
   117  	copy(hBytes[:], digest[:])
   118  	edwards25519.GeScalarMultBase(&A, &hBytes)
   119  	var publicKeyBytes [32]byte
   120  	A.ToBytes(&publicKeyBytes)
   121  
   122  	privateKey := make([]byte, PrivateKeySize)
   123  	copy(privateKey, seed)
   124  	copy(privateKey[32:], publicKeyBytes[:])
   125  
   126  	return privateKey
   127  }
   128  
   129  // Sign signs the message with privateKey and returns a signature. It will
   130  // panic if len(privateKey) is not PrivateKeySize.
   131  func Sign(privateKey PrivateKey, message []byte) []byte {
   132  	if l := len(privateKey); l != PrivateKeySize {
   133  		panic("ed25519: bad private key length: " + strconv.Itoa(l))
   134  	}
   135  
   136  	h := sha512.New()
   137  	h.Write(privateKey[:32])
   138  
   139  	var digest1, messageDigest, hramDigest [64]byte
   140  	var expandedSecretKey [32]byte
   141  	h.Sum(digest1[:0])
   142  	copy(expandedSecretKey[:], digest1[:])
   143  	expandedSecretKey[0] &= 248
   144  	expandedSecretKey[31] &= 63
   145  	expandedSecretKey[31] |= 64
   146  
   147  	h.Reset()
   148  	h.Write(digest1[32:])
   149  	h.Write(message)
   150  	h.Sum(messageDigest[:0])
   151  
   152  	var messageDigestReduced [32]byte
   153  	edwards25519.ScReduce(&messageDigestReduced, &messageDigest)
   154  	var R edwards25519.ExtendedGroupElement
   155  	edwards25519.GeScalarMultBase(&R, &messageDigestReduced)
   156  
   157  	var encodedR [32]byte
   158  	R.ToBytes(&encodedR)
   159  
   160  	h.Reset()
   161  	h.Write(encodedR[:])
   162  	h.Write(privateKey[32:])
   163  	h.Write(message)
   164  	h.Sum(hramDigest[:0])
   165  	var hramDigestReduced [32]byte
   166  	edwards25519.ScReduce(&hramDigestReduced, &hramDigest)
   167  
   168  	var s [32]byte
   169  	edwards25519.ScMulAdd(&s, &hramDigestReduced, &expandedSecretKey, &messageDigestReduced)
   170  
   171  	signature := make([]byte, SignatureSize)
   172  	copy(signature[:], encodedR[:])
   173  	copy(signature[32:], s[:])
   174  
   175  	return signature
   176  }
   177  
   178  // Verify reports whether sig is a valid signature of message by publicKey. It
   179  // will panic if len(publicKey) is not PublicKeySize.
   180  func Verify(publicKey PublicKey, message, sig []byte) bool {
   181  	if l := len(publicKey); l != PublicKeySize {
   182  		panic("ed25519: bad public key length: " + strconv.Itoa(l))
   183  	}
   184  
   185  	if len(sig) != SignatureSize || sig[63]&224 != 0 {
   186  		return false
   187  	}
   188  
   189  	var A edwards25519.ExtendedGroupElement
   190  	var publicKeyBytes [32]byte
   191  	copy(publicKeyBytes[:], publicKey)
   192  	if !A.FromBytes(&publicKeyBytes) {
   193  		return false
   194  	}
   195  	edwards25519.FeNeg(&A.X, &A.X)
   196  	edwards25519.FeNeg(&A.T, &A.T)
   197  
   198  	h := sha512.New()
   199  	h.Write(sig[:32])
   200  	h.Write(publicKey[:])
   201  	h.Write(message)
   202  	var digest [64]byte
   203  	h.Sum(digest[:0])
   204  
   205  	var hReduced [32]byte
   206  	edwards25519.ScReduce(&hReduced, &digest)
   207  
   208  	var R edwards25519.ProjectiveGroupElement
   209  	var s [32]byte
   210  	copy(s[:], sig[32:])
   211  
   212  	// https://tools.ietf.org/html/rfc8032#section-5.1.7 requires that s be in
   213  	// the range [0, order) in order to prevent signature malleability.
   214  	if !edwards25519.ScMinimal(&s) {
   215  		return false
   216  	}
   217  
   218  	edwards25519.GeDoubleScalarMultVartime(&R, &hReduced, &A, &s)
   219  
   220  	var checkR [32]byte
   221  	R.ToBytes(&checkR)
   222  	return bytes.Equal(sig[:32], checkR[:])
   223  }
   224
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