Function Sign

crypto/secp256k1/secp256.go:66–95

Sign creates a recoverable ECDSA signature. The produced signature is in the 65-byte [R || S || V] format where V is 0 or 1. The caller is responsible for ensuring that msg cannot be chosen directly by an attacker. It is usually preferable to use a cryptographic hash function on any input before ha

(msg []byte, seckey []byte)

// directly by an attacker. It is usually preferable to use a cryptographic
// hash function on any input before handing it to this function.
func Sign(msg []byte, seckey []byte) ([]byte, error) {
	if len(msg) != 32 {
		return nil, ErrInvalidMsgLen
	}
	if len(seckey) != 32 {
		return nil, ErrInvalidKey
	}
	seckeydata := (*C.uchar)(unsafe.Pointer(&seckey[0]))
	if C.secp256k1_ec_seckey_verify(context, seckeydata) != 1 {
		return nil, ErrInvalidKey
	}

	var (
		msgdata   = (*C.uchar)(unsafe.Pointer(&msg[0]))
		noncefunc = C.cql_secp256k1_nonce_function_rfc6979
		sigstruct C.secp256k1_ecdsa_recoverable_signature
	)
	if C.secp256k1_ecdsa_sign_recoverable(context, &sigstruct, msgdata, seckeydata, noncefunc, nil) == 0 {
		return nil, ErrSignFailed
	}

	var (
		sig     = make([]byte, 65)
		sigdata = (*C.uchar)(unsafe.Pointer(&sig[0]))
		recid   C.int
	)
	C.secp256k1_ecdsa_recoverable_signature_serialize_compact(context, sigdata, &recid, &sigstruct)
	sig[64] = byte(recid) // add back recid to get 65 bytes sig
	return sig, nil
}

// RecoverPubkey returns the public key of the signer.
// msg must be the 32-byte hash of the message to be signed.