172 lines
5.2 KiB
C++
172 lines
5.2 KiB
C++
/* -*- c++ -*- */
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/*
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* @file
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* @author (C) 2014 by Piotr Krysik <ptrkrysik@gmail.com>
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* @author (C) 2015 by Roman Khassraf <rkhassraf@gmail.com>
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* @section LICENSE
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*
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* Gr-gsm is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 3, or (at your option)
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* any later version.
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*
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* Gr-gsm is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with gr-gsm; see the file COPYING. If not, write to
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* the Free Software Foundation, Inc., 51 Franklin Street,
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* Boston, MA 02110-1301, USA.
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*/
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#ifdef HAVE_CONFIG_H
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#include "config.h"
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#endif
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#include <gnuradio/io_signature.h>
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#include <grgsm/gsmtap.h>
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#include <grgsm/endian.h>
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#include <numeric>
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#include "decryption_impl.h"
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extern "C" {
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#include <osmocom/gsm/a5.h>
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}
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const uint32_t BURST_SIZE=148;
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namespace gr {
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namespace gsm {
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decryption::sptr
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decryption::make(const std::vector<uint8_t> & k_c, unsigned int a5_version)
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{
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return gnuradio::get_initial_sptr
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(new decryption_impl(k_c, a5_version));
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}
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/*
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* The private constructor
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*/
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decryption_impl::decryption_impl(const std::vector<uint8_t> & k_c, unsigned int a5_version)
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: gr::block("decryption",
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gr::io_signature::make(0, 0, 0),
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gr::io_signature::make(0, 0, 0)),
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d_k_c_valid(false)
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{
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set_k_c(k_c);
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set_a5_version(a5_version);
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validate_k_c();
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message_port_register_in(pmt::mp("bursts"));
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set_msg_handler(pmt::mp("bursts"), boost::bind(&decryption_impl::decrypt, this, boost::placeholders::_1));
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message_port_register_out(pmt::mp("bursts"));
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}
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/*
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* Virtual destructor
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*/
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decryption_impl::~decryption_impl()
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{
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}
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void decryption_impl::set_k_c(const std::vector<uint8_t> & k_c)
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{
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d_k_c = k_c;
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}
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void decryption_impl::set_a5_version(unsigned int a5_version)
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{
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d_a5_version = 1;
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if (a5_version >= 1 && a5_version <= 4)
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{
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d_a5_version = a5_version;
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}
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}
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void decryption_impl::validate_k_c()
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{
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if (d_k_c.size() == 0)
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{
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d_k_c_valid = false;
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return;
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}
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else if ((d_a5_version < 4 && d_k_c.size() != 8) || (d_a5_version == 4 && d_k_c.size() != 16))
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{
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d_k_c_valid = false;
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return;
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}
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else
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{
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for (int i=0; i<d_k_c.size(); i++)
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{
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if (d_k_c[i] != 0)
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{
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d_k_c_valid = true;
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return;
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}
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}
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}
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}
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void decryption_impl::decrypt(pmt::pmt_t msg)
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{
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if (!d_k_c_valid)
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{
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message_port_pub(pmt::mp("bursts"), msg);
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}
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else
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{
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uint8_t decrypted_data[BURST_SIZE];
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uint8_t keystream[114];
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pmt::pmt_t header_plus_burst = pmt::cdr(msg);
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gsmtap_hdr * header = (gsmtap_hdr *)pmt::blob_data(header_plus_burst);
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uint8_t * burst_binary = (uint8_t *)(pmt::blob_data(header_plus_burst))+sizeof(gsmtap_hdr);
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uint32_t frame_number = be32toh(header->frame_number);
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bool uplink_burst = (be16toh(header->arfcn) & 0x4000) ? true : false;
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if(uplink_burst){
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//process uplink burst
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osmo_a5(d_a5_version, &d_k_c[0], frame_number, NULL, keystream);
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} else {
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//process downlink burst
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osmo_a5(d_a5_version, &d_k_c[0], frame_number, keystream, NULL);
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}
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/* guard bits */
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for (int i = 0; i < 3; i++) {
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decrypted_data[i] = burst_binary[i];
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}
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//decrypt first part of the burst
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for (int i = 0; i < 57; i++) {
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decrypted_data[i+3] = keystream[i] ^ burst_binary[i+3];
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}
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/* stealing bits and midamble */
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for (int i = 60; i < 88; i++) {
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decrypted_data[i] = burst_binary[i];
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}
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//decrypt second part of the burst
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for (int i = 0; i < 57; i++) {
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decrypted_data[i+88] = keystream[i+57] ^ burst_binary[i+88];
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}
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/* guard bits */
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for (int i = 145; i < 148; i++) {
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decrypted_data[i] = burst_binary[i];
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}
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uint8_t new_header_plus_burst[sizeof(gsmtap_hdr)+BURST_SIZE];
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memcpy(new_header_plus_burst, header, sizeof(gsmtap_hdr));
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memcpy(new_header_plus_burst+sizeof(gsmtap_hdr), decrypted_data, BURST_SIZE);
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pmt::pmt_t msg_binary_blob = pmt::make_blob(new_header_plus_burst, sizeof(gsmtap_hdr)+BURST_SIZE);
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pmt::pmt_t msg_out = pmt::cons(pmt::PMT_NIL, msg_binary_blob);
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message_port_pub(pmt::mp("bursts"), msg_out);
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}
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return;
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}
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} /* namespace gsm */
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} /* namespace gr */
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