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// Copyright 2017 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 !cgo
package crypto
import (
"crypto/ecdsa"
"crypto/elliptic"
"errors"
"fmt"
"math/big"
"github.com/btcsuite/btcd/btcec"
)
// Ecrecover returns the uncompressed public key that created the given signature.
func Ecrecover(hash, sig []byte) ([]byte, error) {
pub, err := SigToPub(hash, sig)
if err != nil {
return nil, err
}
bytes := (*btcec.PublicKey)(pub).SerializeUncompressed()
return bytes, err
}
// SigToPub returns the public key that created the given signature.
func SigToPub(hash, sig []byte) (*ecdsa.PublicKey, error) {
// Convert to btcec input format with 'recovery id' v at the beginning.
btcsig := make([]byte, SignatureLength)
btcsig[0] = sig[64] + 27
copy(btcsig[1:], sig)
pub, _, err := btcec.RecoverCompact(btcec.S256(), btcsig, hash)
return (*ecdsa.PublicKey)(pub), err
}
// 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) ([]byte, error) {
if len(hash) != 32 {
return nil, fmt.Errorf("hash is required to be exactly 32 bytes (%d)", len(hash))
}
if prv.Curve != btcec.S256() {
return nil, fmt.Errorf("private key curve is not secp256k1")
}
sig, err := btcec.SignCompact(btcec.S256(), (*btcec.PrivateKey)(prv), hash, false)
if err != nil {
return nil, err
}
// Convert to Ethereum signature format with 'recovery id' v at the end.
v := sig[0] - 27
copy(sig, sig[1:])
sig[64] = v
return sig, nil
}
// VerifySignature checks that the given public key created signature over hash.
// The public key should be in compressed (33 bytes) or uncompressed (65 bytes) format.
// The signature should have the 64 byte [R || S] format.
func VerifySignature(pubkey, hash, signature []byte) bool {
if len(signature) != 64 {
return false
}
sig := &btcec.Signature{R: new(big.Int).SetBytes(signature[:32]), S: new(big.Int).SetBytes(signature[32:])}
key, err := btcec.ParsePubKey(pubkey, btcec.S256())
if err != nil {
return false
}
// Reject malleable signatures. libsecp256k1 does this check but btcec doesn't.
if sig.S.Cmp(secp256k1halfN) > 0 {
return false
}
return sig.Verify(hash, key)
}
// DecompressPubkey parses a public key in the 33-byte compressed format.
func DecompressPubkey(pubkey []byte) (*ecdsa.PublicKey, error) {
if len(pubkey) != 33 {
return nil, errors.New("invalid compressed public key length")
}
key, err := btcec.ParsePubKey(pubkey, btcec.S256())
if err != nil {
return nil, err
}
return key.ToECDSA(), nil
}
// CompressPubkey encodes a public key to the 33-byte compressed format.
func CompressPubkey(pubkey *ecdsa.PublicKey) []byte {
return (*btcec.PublicKey)(pubkey).SerializeCompressed()
}
// S256 returns an instance of the secp256k1 curve.
func S256() elliptic.Curve {
return btcec.S256()
}
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