update vendor keybase/go-crypto (#10234)

vendor/github.com/keybase/go-crypto/ed25519/ed25519.go

@@ -3,20 +3,23 @@
 // license that can be found in the LICENSE file.
 
 // Package ed25519 implements the Ed25519 signature algorithm. See
-// http://ed25519.cr.yp.to/.
+// https://ed25519.cr.yp.to/.
 //
 // These functions are also compatible with the “Ed25519” function defined in
-// https://tools.ietf.org/html/draft-irtf-cfrg-eddsa-05.
+// 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
 
 // This code is a port of the public domain, “ref10” implementation of ed25519
 // from SUPERCOP.
 
 import (
+	"bytes"
 	"crypto"
 	cryptorand "crypto/rand"
 	"crypto/sha512"
-	"crypto/subtle"
 	"errors"
 	"io"
 	"strconv"
@@ -31,6 +34,8 @@ const (
 	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.
@@ -46,6 +51,15 @@ func (priv PrivateKey) Public() crypto.PublicKey {
 	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
@@ -61,19 +75,33 @@ func (priv PrivateKey) Sign(rand io.Reader, message []byte, opts crypto.SignerOp
 
 // 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 PublicKey, privateKey PrivateKey, err error) {
+func GenerateKey(rand io.Reader) (PublicKey, PrivateKey, error) {
 	if rand == nil {
 		rand = cryptorand.Reader
 	}
 
-	privateKey = make([]byte, PrivateKeySize)
-	publicKey = make([]byte, PublicKeySize)
-	_, err = io.ReadFull(rand, privateKey[:32])
-	if err != nil {
+	seed := make([]byte, SeedSize)
+	if _, err := io.ReadFull(rand, seed); err != nil {
 		return nil, nil, err
 	}
 
-	digest := sha512.Sum512(privateKey[:32])
+	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 {
+	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
@@ -85,10 +113,11 @@ func GenerateKey(rand io.Reader) (publicKey PublicKey, privateKey PrivateKey, er
 	var publicKeyBytes [32]byte
 	A.ToBytes(&publicKeyBytes)
 
+	privateKey := make([]byte, PrivateKeySize)
+	copy(privateKey, seed)
 	copy(privateKey[32:], publicKeyBytes[:])
-	copy(publicKey, publicKeyBytes[:])
 
-	return publicKey, privateKey, nil
+	return privateKey
 }
 
 // Sign signs the message with privateKey and returns a signature. It will
@@ -171,11 +200,18 @@ func Verify(publicKey PublicKey, message, sig []byte) bool {
 	edwards25519.ScReduce(&hReduced, &digest)
 
 	var R edwards25519.ProjectiveGroupElement
-	var b [32]byte
-	copy(b[:], sig[32:])
-	edwards25519.GeDoubleScalarMultVartime(&R, &hReduced, &A, &b)
+	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 subtle.ConstantTimeCompare(sig[:32], checkR[:]) == 1
+	return bytes.Equal(sig[:32], checkR[:])
 }