1 files changed, 344 insertions, 0 deletions
diff --git a/src/crypto/ed25519/ed25519.go b/src/crypto/ed25519/ed25519.go
new file mode 100644
index 0000000..1dda9e5
--- /dev/null
+++ b/src/crypto/ed25519/ed25519.go
@@ -0,0 +1,344 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package ed25519 implements the Ed25519 signature algorithm. See
+// https://ed25519.cr.yp.to/.
+//
+// These functions are also compatible with the “Ed25519” function defined in
+// RFC 8032. However, unlike RFC 8032's formulation, this package's private key
+// representation includes a public key suffix to make multiple signing
+// operations with the same key more efficient. This package refers to the RFC
+// 8032 private key as the “seed”.
+package ed25519
+
+import (
+	"bytes"
+	"crypto"
+	"crypto/internal/edwards25519"
+	cryptorand "crypto/rand"
+	"crypto/sha512"
+	"crypto/subtle"
+	"errors"
+	"io"
+	"strconv"
+)
+
+const (
+	// PublicKeySize is the size, in bytes, of public keys as used in this package.
+	PublicKeySize = 32
+	// PrivateKeySize is the size, in bytes, of private keys as used in this package.
+	PrivateKeySize = 64
+	// SignatureSize is the size, in bytes, of signatures generated and verified by this package.
+	SignatureSize = 64
+	// SeedSize is the size, in bytes, of private key seeds. These are the private key representations used by RFC 8032.
+	SeedSize = 32
+)
+
+// PublicKey is the type of Ed25519 public keys.
+type PublicKey []byte
+
+// Any methods implemented on PublicKey might need to also be implemented on
+// PrivateKey, as the latter embeds the former and will expose its methods.
+
+// Equal reports whether pub and x have the same value.
+func (pub PublicKey) Equal(x crypto.PublicKey) bool {
+	xx, ok := x.(PublicKey)
+	if !ok {
+		return false
+	}
+	return subtle.ConstantTimeCompare(pub, xx) == 1
+}
+
+// PrivateKey is the type of Ed25519 private keys. It implements [crypto.Signer].
+type PrivateKey []byte
+
+// Public returns the [PublicKey] corresponding to priv.
+func (priv PrivateKey) Public() crypto.PublicKey {
+	publicKey := make([]byte, PublicKeySize)
+	copy(publicKey, priv[32:])
+	return PublicKey(publicKey)
+}
+
+// Equal reports whether priv and x have the same value.
+func (priv PrivateKey) Equal(x crypto.PrivateKey) bool {
+	xx, ok := x.(PrivateKey)
+	if !ok {
+		return false
+	}
+	return subtle.ConstantTimeCompare(priv, xx) == 1
+}
+
+// Seed returns the private key seed corresponding to priv. It is provided for
+// interoperability with RFC 8032. RFC 8032's private keys correspond to seeds
+// in this package.
+func (priv PrivateKey) Seed() []byte {
+	return bytes.Clone(priv[:SeedSize])
+}
+
+// Sign signs the given message with priv. rand is ignored and can be nil.
+//
+// If opts.HashFunc() is [crypto.SHA512], the pre-hashed variant Ed25519ph is used
+// and message is expected to be a SHA-512 hash, otherwise opts.HashFunc() must
+// be [crypto.Hash](0) and the message must not be hashed, as Ed25519 performs two
+// passes over messages to be signed.
+//
+// A value of type [Options] can be used as opts, or crypto.Hash(0) or
+// crypto.SHA512 directly to select plain Ed25519 or Ed25519ph, respectively.
+func (priv PrivateKey) Sign(rand io.Reader, message []byte, opts crypto.SignerOpts) (signature []byte, err error) {
+	hash := opts.HashFunc()
+	context := ""
+	if opts, ok := opts.(*Options); ok {
+		context = opts.Context
+	}
+	switch {
+	case hash == crypto.SHA512: // Ed25519ph
+		if l := len(message); l != sha512.Size {
+			return nil, errors.New("ed25519: bad Ed25519ph message hash length: " + strconv.Itoa(l))
+		}
+		if l := len(context); l > 255 {
+			return nil, errors.New("ed25519: bad Ed25519ph context length: " + strconv.Itoa(l))
+		}
+		signature := make([]byte, SignatureSize)
+		sign(signature, priv, message, domPrefixPh, context)
+		return signature, nil
+	case hash == crypto.Hash(0) && context != "": // Ed25519ctx
+		if l := len(context); l > 255 {
+			return nil, errors.New("ed25519: bad Ed25519ctx context length: " + strconv.Itoa(l))
+		}
+		signature := make([]byte, SignatureSize)
+		sign(signature, priv, message, domPrefixCtx, context)
+		return signature, nil
+	case hash == crypto.Hash(0): // Ed25519
+		return Sign(priv, message), nil
+	default:
+		return nil, errors.New("ed25519: expected opts.HashFunc() zero (unhashed message, for standard Ed25519) or SHA-512 (for Ed25519ph)")
+	}
+}
+
+// Options can be used with [PrivateKey.Sign] or [VerifyWithOptions]
+// to select Ed25519 variants.
+type Options struct {
+	// Hash can be zero for regular Ed25519, or crypto.SHA512 for Ed25519ph.
+	Hash crypto.Hash
+
+	// Context, if not empty, selects Ed25519ctx or provides the context string
+	// for Ed25519ph. It can be at most 255 bytes in length.
+	Context string
+}
+
+// HashFunc returns o.Hash.
+func (o *Options) HashFunc() crypto.Hash { return o.Hash }
+
+// GenerateKey generates a public/private key pair using entropy from rand.
+// If rand is nil, [crypto/rand.Reader] will be used.
+//
+// The output of this function is deterministic, and equivalent to reading
+// [SeedSize] bytes from rand, and passing them to [NewKeyFromSeed].
+func GenerateKey(rand io.Reader) (PublicKey, PrivateKey, error) {
+	if rand == nil {
+		rand = cryptorand.Reader
+	}
+
+	seed := make([]byte, SeedSize)
+	if _, err := io.ReadFull(rand, seed); err != nil {
+		return nil, nil, err
+	}
+
+	privateKey := NewKeyFromSeed(seed)
+	publicKey := make([]byte, PublicKeySize)
+	copy(publicKey, privateKey[32:])
+
+	return publicKey, privateKey, nil
+}
+
+// NewKeyFromSeed calculates a private key from a seed. It will panic if
+// len(seed) is not [SeedSize]. This function is provided for interoperability
+// with RFC 8032. RFC 8032's private keys correspond to seeds in this
+// package.
+func NewKeyFromSeed(seed []byte) PrivateKey {
+	// Outline the function body so that the returned key can be stack-allocated.
+	privateKey := make([]byte, PrivateKeySize)
+	newKeyFromSeed(privateKey, seed)
+	return privateKey
+}
+
+func newKeyFromSeed(privateKey, seed []byte) {
+	if l := len(seed); l != SeedSize {
+		panic("ed25519: bad seed length: " + strconv.Itoa(l))
+	}
+
+	h := sha512.Sum512(seed)
+	s, err := edwards25519.NewScalar().SetBytesWithClamping(h[:32])
+	if err != nil {
+		panic("ed25519: internal error: setting scalar failed")
+	}
+	A := (&edwards25519.Point{}).ScalarBaseMult(s)
+
+	publicKey := A.Bytes()
+
+	copy(privateKey, seed)
+	copy(privateKey[32:], publicKey)
+}
+
+// Sign signs the message with privateKey and returns a signature. It will
+// panic if len(privateKey) is not [PrivateKeySize].
+func Sign(privateKey PrivateKey, message []byte) []byte {
+	// Outline the function body so that the returned signature can be
+	// stack-allocated.
+	signature := make([]byte, SignatureSize)
+	sign(signature, privateKey, message, domPrefixPure, "")
+	return signature
+}
+
+// Domain separation prefixes used to disambiguate Ed25519/Ed25519ph/Ed25519ctx.
+// See RFC 8032, Section 2 and Section 5.1.
+const (
+	// domPrefixPure is empty for pure Ed25519.
+	domPrefixPure = ""
+	// domPrefixPh is dom2(phflag=1) for Ed25519ph. It must be followed by the
+	// uint8-length prefixed context.
+	domPrefixPh = "SigEd25519 no Ed25519 collisions\x01"
+	// domPrefixCtx is dom2(phflag=0) for Ed25519ctx. It must be followed by the
+	// uint8-length prefixed context.
+	domPrefixCtx = "SigEd25519 no Ed25519 collisions\x00"
+)
+
+func sign(signature, privateKey, message []byte, domPrefix, context string) {
+	if l := len(privateKey); l != PrivateKeySize {
+		panic("ed25519: bad private key length: " + strconv.Itoa(l))
+	}
+	seed, publicKey := privateKey[:SeedSize], privateKey[SeedSize:]
+
+	h := sha512.Sum512(seed)
+	s, err := edwards25519.NewScalar().SetBytesWithClamping(h[:32])
+	if err != nil {
+		panic("ed25519: internal error: setting scalar failed")
+	}
+	prefix := h[32:]
+
+	mh := sha512.New()
+	if domPrefix != domPrefixPure {
+		mh.Write([]byte(domPrefix))
+		mh.Write([]byte{byte(len(context))})
+		mh.Write([]byte(context))
+	}
+	mh.Write(prefix)
+	mh.Write(message)
+	messageDigest := make([]byte, 0, sha512.Size)
+	messageDigest = mh.Sum(messageDigest)
+	r, err := edwards25519.NewScalar().SetUniformBytes(messageDigest)
+	if err != nil {
+		panic("ed25519: internal error: setting scalar failed")
+	}
+
+	R := (&edwards25519.Point{}).ScalarBaseMult(r)
+
+	kh := sha512.New()
+	if domPrefix != domPrefixPure {
+		kh.Write([]byte(domPrefix))
+		kh.Write([]byte{byte(len(context))})
+		kh.Write([]byte(context))
+	}
+	kh.Write(R.Bytes())
+	kh.Write(publicKey)
+	kh.Write(message)
+	hramDigest := make([]byte, 0, sha512.Size)
+	hramDigest = kh.Sum(hramDigest)
+	k, err := edwards25519.NewScalar().SetUniformBytes(hramDigest)
+	if err != nil {
+		panic("ed25519: internal error: setting scalar failed")
+	}
+
+	S := edwards25519.NewScalar().MultiplyAdd(k, s, r)
+
+	copy(signature[:32], R.Bytes())
+	copy(signature[32:], S.Bytes())
+}
+
+// Verify reports whether sig is a valid signature of message by publicKey. It
+// will panic if len(publicKey) is not [PublicKeySize].
+func Verify(publicKey PublicKey, message, sig []byte) bool {
+	return verify(publicKey, message, sig, domPrefixPure, "")
+}
+
+// VerifyWithOptions reports whether sig is a valid signature of message by
+// publicKey. A valid signature is indicated by returning a nil error. It will
+// panic if len(publicKey) is not [PublicKeySize].
+//
+// If opts.Hash is [crypto.SHA512], the pre-hashed variant Ed25519ph is used and
+// message is expected to be a SHA-512 hash, otherwise opts.Hash must be
+// [crypto.Hash](0) and the message must not be hashed, as Ed25519 performs two
+// passes over messages to be signed.
+func VerifyWithOptions(publicKey PublicKey, message, sig []byte, opts *Options) error {
+	switch {
+	case opts.Hash == crypto.SHA512: // Ed25519ph
+		if l := len(message); l != sha512.Size {
+			return errors.New("ed25519: bad Ed25519ph message hash length: " + strconv.Itoa(l))
+		}
+		if l := len(opts.Context); l > 255 {
+			return errors.New("ed25519: bad Ed25519ph context length: " + strconv.Itoa(l))
+		}
+		if !verify(publicKey, message, sig, domPrefixPh, opts.Context) {
+			return errors.New("ed25519: invalid signature")
+		}
+		return nil
+	case opts.Hash == crypto.Hash(0) && opts.Context != "": // Ed25519ctx
+		if l := len(opts.Context); l > 255 {
+			return errors.New("ed25519: bad Ed25519ctx context length: " + strconv.Itoa(l))
+		}
+		if !verify(publicKey, message, sig, domPrefixCtx, opts.Context) {
+			return errors.New("ed25519: invalid signature")
+		}
+		return nil
+	case opts.Hash == crypto.Hash(0): // Ed25519
+		if !verify(publicKey, message, sig, domPrefixPure, "") {
+			return errors.New("ed25519: invalid signature")
+		}
+		return nil
+	default:
+		return errors.New("ed25519: expected opts.Hash zero (unhashed message, for standard Ed25519) or SHA-512 (for Ed25519ph)")
+	}
+}
+
+func verify(publicKey PublicKey, message, sig []byte, domPrefix, context string) bool {
+	if l := len(publicKey); l != PublicKeySize {
+		panic("ed25519: bad public key length: " + strconv.Itoa(l))
+	}
+
+	if len(sig) != SignatureSize || sig[63]&224 != 0 {
+		return false
+	}
+
+	A, err := (&edwards25519.Point{}).SetBytes(publicKey)
+	if err != nil {
+		return false
+	}
+
+	kh := sha512.New()
+	if domPrefix != domPrefixPure {
+		kh.Write([]byte(domPrefix))
+		kh.Write([]byte{byte(len(context))})
+		kh.Write([]byte(context))
+	}
+	kh.Write(sig[:32])
+	kh.Write(publicKey)
+	kh.Write(message)
+	hramDigest := make([]byte, 0, sha512.Size)
+	hramDigest = kh.Sum(hramDigest)
+	k, err := edwards25519.NewScalar().SetUniformBytes(hramDigest)
+	if err != nil {
+		panic("ed25519: internal error: setting scalar failed")
+	}
+
+	S, err := edwards25519.NewScalar().SetCanonicalBytes(sig[32:])
+	if err != nil {
+		return false
+	}
+
+	// [S]B = R + [k]A --> [k](-A) + [S]B = R
+	minusA := (&edwards25519.Point{}).Negate(A)
+	R := (&edwards25519.Point{}).VarTimeDoubleScalarBaseMult(k, minusA, S)
+
+	return bytes.Equal(sig[:32], R.Bytes())
+}