mirror of https://go.googlesource.com/go
354 lines
12 KiB
Go
354 lines
12 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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// 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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//
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// Operations involving private keys are implemented using constant-time
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// algorithms.
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package ed25519
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import (
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"bytes"
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"crypto"
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"crypto/internal/edwards25519"
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cryptorand "crypto/rand"
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"crypto/sha512"
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"crypto/subtle"
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"errors"
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"io"
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"strconv"
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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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// Any methods implemented on PublicKey might need to also be implemented on
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// PrivateKey, as the latter embeds the former and will expose its methods.
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// Equal reports whether pub and x have the same value.
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func (pub PublicKey) Equal(x crypto.PublicKey) bool {
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xx, ok := x.(PublicKey)
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if !ok {
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return false
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}
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return subtle.ConstantTimeCompare(pub, xx) == 1
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}
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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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// Equal reports whether priv and x have the same value.
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func (priv PrivateKey) Equal(x crypto.PrivateKey) bool {
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xx, ok := x.(PrivateKey)
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if !ok {
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return false
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}
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return subtle.ConstantTimeCompare(priv, xx) == 1
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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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return bytes.Clone(priv[:SeedSize])
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}
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// Sign signs the given message with priv. rand is ignored and can be nil.
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//
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// If opts.HashFunc() is [crypto.SHA512], the pre-hashed variant Ed25519ph is used
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// and message is expected to be a SHA-512 hash, otherwise opts.HashFunc() must
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// be [crypto.Hash](0) and the message must not be hashed, as Ed25519 performs two
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// passes over messages to be signed.
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//
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// A value of type [Options] can be used as opts, or crypto.Hash(0) or
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// crypto.SHA512 directly to select plain Ed25519 or Ed25519ph, respectively.
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func (priv PrivateKey) Sign(rand io.Reader, message []byte, opts crypto.SignerOpts) (signature []byte, err error) {
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hash := opts.HashFunc()
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context := ""
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if opts, ok := opts.(*Options); ok {
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context = opts.Context
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}
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switch {
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case hash == crypto.SHA512: // Ed25519ph
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if l := len(message); l != sha512.Size {
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return nil, errors.New("ed25519: bad Ed25519ph message hash length: " + strconv.Itoa(l))
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}
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if l := len(context); l > 255 {
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return nil, errors.New("ed25519: bad Ed25519ph context length: " + strconv.Itoa(l))
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}
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signature := make([]byte, SignatureSize)
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sign(signature, priv, message, domPrefixPh, context)
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return signature, nil
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case hash == crypto.Hash(0) && context != "": // Ed25519ctx
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if l := len(context); l > 255 {
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return nil, errors.New("ed25519: bad Ed25519ctx context length: " + strconv.Itoa(l))
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}
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signature := make([]byte, SignatureSize)
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sign(signature, priv, message, domPrefixCtx, context)
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return signature, nil
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case hash == crypto.Hash(0): // Ed25519
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return Sign(priv, message), nil
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default:
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return nil, errors.New("ed25519: expected opts.HashFunc() zero (unhashed message, for standard Ed25519) or SHA-512 (for Ed25519ph)")
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}
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}
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// Options can be used with [PrivateKey.Sign] or [VerifyWithOptions]
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// to select Ed25519 variants.
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type Options struct {
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// Hash can be zero for regular Ed25519, or crypto.SHA512 for Ed25519ph.
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Hash crypto.Hash
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// Context, if not empty, selects Ed25519ctx or provides the context string
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// for Ed25519ph. It can be at most 255 bytes in length.
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Context string
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}
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// HashFunc returns o.Hash.
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func (o *Options) HashFunc() crypto.Hash { return o.Hash }
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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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//
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// The output of this function is deterministic, and equivalent to reading
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// [SeedSize] bytes from rand, and passing them to [NewKeyFromSeed].
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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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// Outline the function body so that the returned key can be stack-allocated.
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privateKey := make([]byte, PrivateKeySize)
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newKeyFromSeed(privateKey, seed)
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return privateKey
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}
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func newKeyFromSeed(privateKey, seed []byte) {
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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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h := sha512.Sum512(seed)
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s, err := edwards25519.NewScalar().SetBytesWithClamping(h[:32])
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if err != nil {
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panic("ed25519: internal error: setting scalar failed")
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}
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A := (&edwards25519.Point{}).ScalarBaseMult(s)
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publicKey := A.Bytes()
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copy(privateKey, seed)
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copy(privateKey[32:], publicKey)
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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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// Outline the function body so that the returned signature can be
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// stack-allocated.
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signature := make([]byte, SignatureSize)
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sign(signature, privateKey, message, domPrefixPure, "")
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return signature
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}
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// Domain separation prefixes used to disambiguate Ed25519/Ed25519ph/Ed25519ctx.
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// See RFC 8032, Section 2 and Section 5.1.
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const (
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// domPrefixPure is empty for pure Ed25519.
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domPrefixPure = ""
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// domPrefixPh is dom2(phflag=1) for Ed25519ph. It must be followed by the
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// uint8-length prefixed context.
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domPrefixPh = "SigEd25519 no Ed25519 collisions\x01"
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// domPrefixCtx is dom2(phflag=0) for Ed25519ctx. It must be followed by the
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// uint8-length prefixed context.
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domPrefixCtx = "SigEd25519 no Ed25519 collisions\x00"
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)
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func sign(signature, privateKey, message []byte, domPrefix, context string) {
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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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seed, publicKey := privateKey[:SeedSize], privateKey[SeedSize:]
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h := sha512.Sum512(seed)
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s, err := edwards25519.NewScalar().SetBytesWithClamping(h[:32])
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if err != nil {
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panic("ed25519: internal error: setting scalar failed")
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}
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prefix := h[32:]
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mh := sha512.New()
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if domPrefix != domPrefixPure {
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mh.Write([]byte(domPrefix))
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mh.Write([]byte{byte(len(context))})
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mh.Write([]byte(context))
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}
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mh.Write(prefix)
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mh.Write(message)
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messageDigest := make([]byte, 0, sha512.Size)
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messageDigest = mh.Sum(messageDigest)
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r, err := edwards25519.NewScalar().SetUniformBytes(messageDigest)
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if err != nil {
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panic("ed25519: internal error: setting scalar failed")
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}
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R := (&edwards25519.Point{}).ScalarBaseMult(r)
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kh := sha512.New()
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if domPrefix != domPrefixPure {
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kh.Write([]byte(domPrefix))
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kh.Write([]byte{byte(len(context))})
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kh.Write([]byte(context))
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}
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kh.Write(R.Bytes())
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kh.Write(publicKey)
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kh.Write(message)
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hramDigest := make([]byte, 0, sha512.Size)
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hramDigest = kh.Sum(hramDigest)
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k, err := edwards25519.NewScalar().SetUniformBytes(hramDigest)
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if err != nil {
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panic("ed25519: internal error: setting scalar failed")
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}
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S := edwards25519.NewScalar().MultiplyAdd(k, s, r)
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copy(signature[:32], R.Bytes())
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copy(signature[32:], S.Bytes())
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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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//
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// The inputs are not considered confidential, and may leak through timing side
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// channels, or if an attacker has control of part of the inputs.
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func Verify(publicKey PublicKey, message, sig []byte) bool {
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return verify(publicKey, message, sig, domPrefixPure, "")
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}
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// VerifyWithOptions reports whether sig is a valid signature of message by
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// publicKey. A valid signature is indicated by returning a nil error. It will
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// panic if len(publicKey) is not [PublicKeySize].
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//
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// If opts.Hash is [crypto.SHA512], the pre-hashed variant Ed25519ph is used and
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// message is expected to be a SHA-512 hash, otherwise opts.Hash must be
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// [crypto.Hash](0) and the message must not be hashed, as Ed25519 performs two
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// passes over messages to be signed.
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//
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// The inputs are not considered confidential, and may leak through timing side
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// channels, or if an attacker has control of part of the inputs.
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func VerifyWithOptions(publicKey PublicKey, message, sig []byte, opts *Options) error {
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switch {
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case opts.Hash == crypto.SHA512: // Ed25519ph
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if l := len(message); l != sha512.Size {
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return errors.New("ed25519: bad Ed25519ph message hash length: " + strconv.Itoa(l))
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}
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if l := len(opts.Context); l > 255 {
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return errors.New("ed25519: bad Ed25519ph context length: " + strconv.Itoa(l))
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}
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if !verify(publicKey, message, sig, domPrefixPh, opts.Context) {
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return errors.New("ed25519: invalid signature")
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}
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return nil
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case opts.Hash == crypto.Hash(0) && opts.Context != "": // Ed25519ctx
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if l := len(opts.Context); l > 255 {
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return errors.New("ed25519: bad Ed25519ctx context length: " + strconv.Itoa(l))
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}
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if !verify(publicKey, message, sig, domPrefixCtx, opts.Context) {
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return errors.New("ed25519: invalid signature")
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}
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return nil
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case opts.Hash == crypto.Hash(0): // Ed25519
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if !verify(publicKey, message, sig, domPrefixPure, "") {
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return errors.New("ed25519: invalid signature")
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}
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return nil
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default:
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return errors.New("ed25519: expected opts.Hash zero (unhashed message, for standard Ed25519) or SHA-512 (for Ed25519ph)")
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}
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}
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func verify(publicKey PublicKey, message, sig []byte, domPrefix, context string) 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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A, err := (&edwards25519.Point{}).SetBytes(publicKey)
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if err != nil {
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return false
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}
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kh := sha512.New()
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if domPrefix != domPrefixPure {
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kh.Write([]byte(domPrefix))
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kh.Write([]byte{byte(len(context))})
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kh.Write([]byte(context))
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}
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kh.Write(sig[:32])
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kh.Write(publicKey)
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kh.Write(message)
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hramDigest := make([]byte, 0, sha512.Size)
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hramDigest = kh.Sum(hramDigest)
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k, err := edwards25519.NewScalar().SetUniformBytes(hramDigest)
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if err != nil {
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panic("ed25519: internal error: setting scalar failed")
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}
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S, err := edwards25519.NewScalar().SetCanonicalBytes(sig[32:])
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if err != nil {
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return false
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}
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// [S]B = R + [k]A --> [k](-A) + [S]B = R
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minusA := (&edwards25519.Point{}).Negate(A)
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R := (&edwards25519.Point{}).VarTimeDoubleScalarBaseMult(k, minusA, S)
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return bytes.Equal(sig[:32], R.Bytes())
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}
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