public void dump(FileOutputStream out) throws Exception {
        out.write(packet_tag & 0xff);
        out.write(packet_length & 0xff);
        out.write(version & 0xff);
        for (int i : key_id)
            out.write(i & 0xff);
        out.write(PKA_id & 0xff);
        encr_key.dump(out);
    }