ed25519: drop Go 1.12 compatibility

x/crypto/ed25519 moved to the standard library in Go 1.13. This change
drops the compatibility wrapper we were keeping around to make Go 1.12
and earlier work.

Change-Id: I860ed963a0660753d01c89014c21360b239a38ac
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/317169
Trust: Filippo Valsorda <filippo@golang.org>
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Katie Hockman <katie@golang.org>
Trust: Katie Hockman <katie@golang.org>

Author: FiloSottile

ed25519/ed25519.go

@@ -1,13 +1,7 @@
-// Copyright 2016 The Go Authors. All rights reserved.
+// Copyright 2019 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.
 
-// In Go 1.13, the ed25519 package was promoted to the standard library as
-// crypto/ed25519, and this package became a wrapper for the standard library one.
-//
-//go:build !go1.13
-// +build !go1.13
-
 // Package ed25519 implements the Ed25519 signature algorithm. See
 // https://ed25519.cr.yp.to/.
 //
@@ -16,21 +10,15 @@
 // 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”.
+//
+// Beginning with Go 1.13, the functionality of this package was moved to the
+// standard library as crypto/ed25519. This package only acts as a compatibility
+// wrapper.
 package ed25519
 
-// This code is a port of the public domain, “ref10” implementation of ed25519
-// from SUPERCOP.
-
 import (
-	"bytes"
-	"crypto"
-	cryptorand "crypto/rand"
-	"crypto/sha512"
-	"errors"
+	"crypto/ed25519"
 	"io"
-	"strconv"
-
-	"golang.org/x/crypto/ed25519/internal/edwards25519"
 )
 
 const (
@@ -45,179 +33,39 @@ const (
 )
 
 // PublicKey is the type of Ed25519 public keys.
-type PublicKey []byte
+//
+// This type is an alias for crypto/ed25519's PublicKey type.
+// See the crypto/ed25519 package for the methods on this type.
+type PublicKey = ed25519.PublicKey
 
 // 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)
-}
-
-// 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 {
-	seed := make([]byte, SeedSize)
-	copy(seed, priv[:32])
-	return seed
-}
-
-// Sign signs the given message with priv.
-// Ed25519 performs two passes over messages to be signed and therefore cannot
-// handle pre-hashed messages. Thus opts.HashFunc() must return zero to
-// indicate the message hasn't been hashed. This can be achieved by passing
-// crypto.Hash(0) as the value for opts.
-func (priv PrivateKey) Sign(rand io.Reader, message []byte, opts crypto.SignerOpts) (signature []byte, err error) {
-	if opts.HashFunc() != crypto.Hash(0) {
-		return nil, errors.New("ed25519: cannot sign hashed message")
-	}
-
-	return Sign(priv, message), nil
-}
+//
+// This type is an alias for crypto/ed25519's PrivateKey type.
+// See the crypto/ed25519 package for the methods on this type.
+type PrivateKey = ed25519.PrivateKey
 
 // GenerateKey generates a public/private key pair using entropy from rand.
 // If rand is nil, crypto/rand.Reader will be used.
 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
+	return ed25519.GenerateKey(rand)
 }
 
 // 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 {
-	if l := len(seed); l != SeedSize {
-		panic("ed25519: bad seed length: " + strconv.Itoa(l))
-	}
-
-	digest := sha512.Sum512(seed)
-	digest[0] &= 248
-	digest[31] &= 127
-	digest[31] |= 64
-
-	var A edwards25519.ExtendedGroupElement
-	var hBytes [32]byte
-	copy(hBytes[:], digest[:])
-	edwards25519.GeScalarMultBase(&A, &hBytes)
-	var publicKeyBytes [32]byte
-	A.ToBytes(&publicKeyBytes)
-
-	privateKey := make([]byte, PrivateKeySize)
-	copy(privateKey, seed)
-	copy(privateKey[32:], publicKeyBytes[:])
-
-	return privateKey
+	return ed25519.NewKeyFromSeed(seed)
 }
 
 // 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 {
-	if l := len(privateKey); l != PrivateKeySize {
-		panic("ed25519: bad private key length: " + strconv.Itoa(l))
-	}
-
-	h := sha512.New()
-	h.Write(privateKey[:32])
-
-	var digest1, messageDigest, hramDigest [64]byte
-	var expandedSecretKey [32]byte
-	h.Sum(digest1[:0])
-	copy(expandedSecretKey[:], digest1[:])
-	expandedSecretKey[0] &= 248
-	expandedSecretKey[31] &= 63
-	expandedSecretKey[31] |= 64
-
-	h.Reset()
-	h.Write(digest1[32:])
-	h.Write(message)
-	h.Sum(messageDigest[:0])
-
-	var messageDigestReduced [32]byte
-	edwards25519.ScReduce(&messageDigestReduced, &messageDigest)
-	var R edwards25519.ExtendedGroupElement
-	edwards25519.GeScalarMultBase(&R, &messageDigestReduced)
-
-	var encodedR [32]byte
-	R.ToBytes(&encodedR)
-
-	h.Reset()
-	h.Write(encodedR[:])
-	h.Write(privateKey[32:])
-	h.Write(message)
-	h.Sum(hramDigest[:0])
-	var hramDigestReduced [32]byte
-	edwards25519.ScReduce(&hramDigestReduced, &hramDigest)
-
-	var s [32]byte
-	edwards25519.ScMulAdd(&s, &hramDigestReduced, &expandedSecretKey, &messageDigestReduced)
-
-	signature := make([]byte, SignatureSize)
-	copy(signature[:], encodedR[:])
-	copy(signature[32:], s[:])
-
-	return signature
+	return ed25519.Sign(privateKey, message)
 }
 
 // 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 {
-	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
-	}
-
-	var A edwards25519.ExtendedGroupElement
-	var publicKeyBytes [32]byte
-	copy(publicKeyBytes[:], publicKey)
-	if !A.FromBytes(&publicKeyBytes) {
-		return false
-	}
-	edwards25519.FeNeg(&A.X, &A.X)
-	edwards25519.FeNeg(&A.T, &A.T)
-
-	h := sha512.New()
-	h.Write(sig[:32])
-	h.Write(publicKey[:])
-	h.Write(message)
-	var digest [64]byte
-	h.Sum(digest[:0])
-
-	var hReduced [32]byte
-	edwards25519.ScReduce(&hReduced, &digest)
-
-	var R edwards25519.ProjectiveGroupElement
-	var s [32]byte
-	copy(s[:], sig[32:])
-
-	// https://tools.ietf.org/html/rfc8032#section-5.1.7 requires that s be in
-	// the range [0, order) in order to prevent signature malleability.
-	if !edwards25519.ScMinimal(&s) {
-		return false
-	}
-
-	edwards25519.GeDoubleScalarMultVartime(&R, &hReduced, &A, &s)
-
-	var checkR [32]byte
-	R.ToBytes(&checkR)
-	return bytes.Equal(sig[:32], checkR[:])
+	return ed25519.Verify(publicKey, message, sig)
 }