crypto: add btcec fallback for sign/recover without cgo (#3680)

* vendor: add github.com/btcsuite/btcd/btcec

* crypto: add btcec fallback for sign/recover without cgo

This commit adds a non-cgo fallback implementation of secp256k1
operations.

* crypto, core/vm: remove wrappers for sha256, ripemd160

crypto/signature_cgo.go

@@ -0,0 +1,64 @@
+// Copyright 2016 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+// +build !nacl,!js,!nocgo
+
+package crypto
+
+import (
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"fmt"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/crypto/secp256k1"
+)
+
+func Ecrecover(hash, sig []byte) ([]byte, error) {
+	return secp256k1.RecoverPubkey(hash, sig)
+}
+
+func SigToPub(hash, sig []byte) (*ecdsa.PublicKey, error) {
+	s, err := Ecrecover(hash, sig)
+	if err != nil {
+		return nil, err
+	}
+
+	x, y := elliptic.Unmarshal(S256(), s)
+	return &ecdsa.PublicKey{Curve: S256(), X: x, Y: y}, nil
+}
+
+// Sign calculates an ECDSA signature.
+//
+// This function is susceptible to chosen plaintext attacks that can leak
+// information about the private key that is used for signing. Callers must
+// be aware that the given hash cannot be chosen by an adversery. Common
+// solution is to hash any input before calculating the signature.
+//
+// The produced signature is in the [R || S || V] format where V is 0 or 1.
+func Sign(hash []byte, prv *ecdsa.PrivateKey) (sig []byte, err error) {
+	if len(hash) != 32 {
+		return nil, fmt.Errorf("hash is required to be exactly 32 bytes (%d)", len(hash))
+	}
+	seckey := common.LeftPadBytes(prv.D.Bytes(), prv.Params().BitSize/8)
+	defer zeroBytes(seckey)
+	return secp256k1.Sign(hash, seckey)
+}
+
+// S256 returns an instance of the secp256k1 curve.
+func S256() elliptic.Curve {
+	return secp256k1.S256()
+}