SEDP(byte[] data, byte len) throws Exception {
        packet_tag = (byte) SEDP_TAG;
        version = 4;
        key_id = (byte) TRIPLEDES_ID;
        s2k = (byte) S2K_reserved;
        cipher_text = data;
        packet_length = (byte) (len + 1 + 1 + 1);  // padded data + version + sym_alg_id + S2K
    }