Use ethereum's secp256k1 lib (#3234)

* switch from fork (tendermint/btcd) to orig package (btcsuite/btcd); also

 - remove obsolete check in test `size != -1` is always true
 - WIP as the serialization still needs to be wrapped

* WIP: wrap signature & privkey, pubkey needs to be wrapped as well

* wrap pubkey too

* use "github.com/ethereum/go-ethereum/crypto/secp256k1" if cgo is
available, else use "github.com/btcsuite/btcd/btcec" and take care of
lower-S when verifying

Annoyingly, had to disable pruning when importing
github.com/ethereum/go-ethereum/ :-/

* update comment

* update comment

* emulate signature_nocgo.go for additional benchmarks:
https://github.com/ethereum/go-ethereum/blob/592bf6a59cac9697f0491b24e5093cb759d7e44c/crypto/signature_nocgo.go#L60-L76

* use our format (r || s) in lower-s form when in the non-cgo case

* remove comment about using the C library directly

* vendor github.com/btcsuite/btcd too

* Add test for the !cgo case

* update changelog pending

Closes #3162 #3163
Refs #1958, #2091, tendermint/btcd#1

crypto/encoding/amino/encode_test.go

@@ -25,9 +25,8 @@ func checkAminoBinary(t *testing.T, src, dst interface{}, size int) {
 		assert.Equal(t, byterSrc.Bytes(), bz, "Amino binary vs Bytes() mismatch")
 	}
 	// Make sure we have the expected length.
-	if size != -1 {
-		assert.Equal(t, size, len(bz), "Amino binary size mismatch")
-	}
+	assert.Equal(t, size, len(bz), "Amino binary size mismatch")
+
 	// Unmarshal.
 	err = cdc.UnmarshalBinaryBare(bz, dst)
 	require.Nil(t, err, "%+v", err)

crypto/secp256k1/secp256k1.go

@@ -7,10 +7,12 @@ import (
 	"fmt"
 	"io"
 
-	secp256k1 "github.com/tendermint/btcd/btcec"
-	amino "github.com/tendermint/go-amino"
 	"golang.org/x/crypto/ripemd160"
 
+	secp256k1 "github.com/btcsuite/btcd/btcec"
+
+	amino "github.com/tendermint/go-amino"
+
 	"github.com/tendermint/tendermint/crypto"
 )
 
@@ -44,16 +46,6 @@ func (privKey PrivKeySecp256k1) Bytes() []byte {
 	return cdc.MustMarshalBinaryBare(privKey)
 }
 
-// Sign creates an ECDSA signature on curve Secp256k1, using SHA256 on the msg.
-func (privKey PrivKeySecp256k1) Sign(msg []byte) ([]byte, error) {
-	priv, _ := secp256k1.PrivKeyFromBytes(secp256k1.S256(), privKey[:])
-	sig, err := priv.Sign(crypto.Sha256(msg))
-	if err != nil {
-		return nil, err
-	}
-	return sig.Serialize(), nil
-}
-
 // PubKey performs the point-scalar multiplication from the privKey on the
 // generator point to get the pubkey.
 func (privKey PrivKeySecp256k1) PubKey() crypto.PubKey {
@@ -137,20 +129,6 @@ func (pubKey PubKeySecp256k1) Bytes() []byte {
 	return bz
 }
 
-func (pubKey PubKeySecp256k1) VerifyBytes(msg []byte, sig []byte) bool {
-	pub, err := secp256k1.ParsePubKey(pubKey[:], secp256k1.S256())
-	if err != nil {
-		return false
-	}
-	parsedSig, err := secp256k1.ParseSignature(sig[:], secp256k1.S256())
-	if err != nil {
-		return false
-	}
-	// Underlying library ensures that this signature is in canonical form, to
-	// prevent Secp256k1 malleability from altering the sign of the s term.
-	return parsedSig.Verify(crypto.Sha256(msg), pub)
-}
-
 func (pubKey PubKeySecp256k1) String() string {
 	return fmt.Sprintf("PubKeySecp256k1{%X}", pubKey[:])
 }

crypto/secp256k1/secp256k1_cgo.go

@@ -0,0 +1,24 @@
+// +build cgo
+
+package secp256k1
+
+import (
+	"github.com/ethereum/go-ethereum/crypto/secp256k1"
+
+	"github.com/tendermint/tendermint/crypto"
+)
+
+// Sign creates an ECDSA signature on curve Secp256k1, using SHA256 on the msg.
+func (privKey PrivKeySecp256k1) Sign(msg []byte) ([]byte, error) {
+	rsv, err := secp256k1.Sign(crypto.Sha256(msg), privKey[:])
+	if err != nil {
+		return nil, err
+	}
+	// we do not need v  in r||s||v:
+	rs := rsv[:len(rsv)-1]
+	return rs, nil
+}
+
+func (pubKey PubKeySecp256k1) VerifyBytes(msg []byte, sig []byte) bool {
+	return secp256k1.VerifySignature(pubKey[:], crypto.Sha256(msg), sig)
+}

crypto/secp256k1/secp256k1_nocgo.go

@@ -0,0 +1,71 @@
+// +build !cgo
+
+package secp256k1
+
+import (
+	"math/big"
+
+	secp256k1 "github.com/btcsuite/btcd/btcec"
+
+	"github.com/tendermint/tendermint/crypto"
+)
+
+// used to reject malleable signatures
+// see:
+//  - https://github.com/ethereum/go-ethereum/blob/f9401ae011ddf7f8d2d95020b7446c17f8d98dc1/crypto/signature_nocgo.go#L90-L93
+//  - https://github.com/ethereum/go-ethereum/blob/f9401ae011ddf7f8d2d95020b7446c17f8d98dc1/crypto/crypto.go#L39
+var secp256k1N, _ = new(big.Int).SetString("fffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141", 16)
+var secp256k1halfN = new(big.Int).Div(secp256k1N, big.NewInt(2))
+
+// Sign creates an ECDSA signature on curve Secp256k1, using SHA256 on the msg.
+// The returned signature will be of the form R || S (in lower-S form).
+func (privKey PrivKeySecp256k1) Sign(msg []byte) ([]byte, error) {
+	priv, _ := secp256k1.PrivKeyFromBytes(secp256k1.S256(), privKey[:])
+	sig, err := priv.Sign(crypto.Sha256(msg))
+	if err != nil {
+		return nil, err
+	}
+	sigBytes := serializeSig(sig)
+	return sigBytes, nil
+}
+
+// VerifyBytes verifies a signature of the form R || S.
+// It rejects signatures which are not in lower-S form.
+func (pubKey PubKeySecp256k1) VerifyBytes(msg []byte, sigStr []byte) bool {
+	if len(sigStr) != 64 {
+		return false
+	}
+	pub, err := secp256k1.ParsePubKey(pubKey[:], secp256k1.S256())
+	if err != nil {
+		return false
+	}
+	// parse the signature:
+	signature := signatureFromBytes(sigStr)
+	// Reject malleable signatures. libsecp256k1 does this check but btcec doesn't.
+	// see: https://github.com/ethereum/go-ethereum/blob/f9401ae011ddf7f8d2d95020b7446c17f8d98dc1/crypto/signature_nocgo.go#L90-L93
+	if signature.S.Cmp(secp256k1halfN) > 0 {
+		return false
+	}
+	return signature.Verify(crypto.Sha256(msg), pub)
+}
+
+// Read Signature struct from R || S. Caller needs to ensure
+// that len(sigStr) == 64.
+func signatureFromBytes(sigStr []byte) *secp256k1.Signature {
+	return &secp256k1.Signature{
+		new(big.Int).SetBytes(sigStr[:32]),
+		new(big.Int).SetBytes(sigStr[32:64]),
+	}
+}
+
+// Serialize signature to R || S.
+// R, S are padded to 32 bytes respectively.
+func serializeSig(sig *secp256k1.Signature) []byte {
+	rBytes := sig.R.Bytes()
+	sBytes := sig.S.Bytes()
+	sigBytes := make([]byte, 64)
+	// 0 pad the byte arrays from the left if they aren't big enough.
+	copy(sigBytes[32-len(rBytes):32], rBytes)
+	copy(sigBytes[64-len(sBytes):64], sBytes)
+	return sigBytes
+}

crypto/secp256k1/secp256k1_nocgo_test.go

@@ -0,0 +1,39 @@
+// +build !cgo
+
+package secp256k1
+
+import (
+	"testing"
+
+	secp256k1 "github.com/btcsuite/btcd/btcec"
+
+	"github.com/stretchr/testify/require"
+)
+
+// Ensure that signature verification works, and that
+// non-canonical signatures fail.
+// Note: run with CGO_ENABLED=0 or go test -tags !cgo.
+func TestSignatureVerificationAndRejectUpperS(t *testing.T) {
+	msg := []byte("We have lingered long enough on the shores of the cosmic ocean.")
+	for i := 0; i < 500; i++ {
+		priv := GenPrivKey()
+		sigStr, err := priv.Sign(msg)
+		require.NoError(t, err)
+		sig := signatureFromBytes(sigStr)
+		require.False(t, sig.S.Cmp(secp256k1halfN) > 0)
+
+		pub := priv.PubKey()
+		require.True(t, pub.VerifyBytes(msg, sigStr))
+
+		// malleate:
+		sig.S.Sub(secp256k1.S256().CurveParams.N, sig.S)
+		require.True(t, sig.S.Cmp(secp256k1halfN) > 0)
+		malSigStr := serializeSig(sig)
+
+		require.False(t, pub.VerifyBytes(msg, malSigStr),
+			"VerifyBytes incorrect with malleated & invalid S. sig=%v, key=%v",
+			sig,
+			priv,
+		)
+	}
+}

crypto/secp256k1/secpk256k1_test.go

@@ -11,7 +11,7 @@ import (
 	"github.com/tendermint/tendermint/crypto"
 	"github.com/tendermint/tendermint/crypto/secp256k1"
 
-	underlyingSecp256k1 "github.com/tendermint/btcd/btcec"
+	underlyingSecp256k1 "github.com/btcsuite/btcd/btcec"
 )
 
 type keyData struct {