code: func HexToECDSA(hexkey string) (*ecdsa.PrivateKey, error) {
  	b, err := hex.DecodeString(hexkey)
  	if err != nil {
  		return nil, errors.New("invalid hex string")
  	}
  	return ToECDSA(b)
  }
docs: // HexToECDSA parses a secp256k1 private key.