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

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