code: func (v *Secp256k1) DecodeRLP(s *rlp.Stream) error {
  	buf, err := s.Bytes()
  	if err != nil {
  		return err
  	}
  	pk, err := crypto.DecompressPubkey(buf)
  	if err != nil {
  		return err
  	}
  	*v = (Secp256k1)(*pk)
  	return nil
  }
docs: // DecodeRLP implements rlp.Decoder.