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