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/* -*- c++ -*- */
/*
* Copyright 2014 <+YOU OR YOUR COMPANY+>.
*
* This 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.
*
* This software 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 this software; 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 "decryption_impl.h"
#include "a5_1_2.h"
const uint32_t BURST_SIZE=148;
namespace gr {
namespace gsm {
decryption::sptr
decryption::make(const std::vector<uint8_t> & k_c)
{
return gnuradio::get_initial_sptr
(new decryption_impl(k_c));
}
/*
* The private constructor
*/
decryption_impl::decryption_impl(const std::vector<uint8_t> & k_c)
: gr::block("decryption",
gr::io_signature::make(0, 0, 0),
gr::io_signature::make(0, 0, 0))
{
set_k_c(k_c);
// std::cout << "Be careful with decryption block - it wasn't tested yet!" << std::endl;
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::decrypt(pmt::pmt_t msg)
{
if(d_k_c.size() != 8){
message_port_pub(pmt::mp("bursts"), msg);
} else
if(d_k_c[0] == 0 && d_k_c[1] == 0 && d_k_c[2] == 0 && d_k_c[3] == 0 &
d_k_c[4] == 0 && d_k_c[5] == 0 && d_k_c[6] == 0 && d_k_c[7] == 0)
{
message_port_pub(pmt::mp("bursts"), msg);
} else
{
uint8_t decrypted_data[BURST_SIZE];
uint8_t AtoBkeystream[114];
uint8_t BtoAkeystream[114];
uint8_t * keystream;
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;
uint32_t t1 = frame_number / (26*51);
uint32_t t2 = frame_number % 26;
uint32_t t3 = frame_number % 51;
uint32_t frame_number_mod = (t1 << 11) + (t3 << 5) + t2;
keysetup(&d_k_c[0], frame_number_mod);
runA51(AtoBkeystream, BtoAkeystream);
if(uplink_burst){
//process uplink burst
keystream = BtoAkeystream;
} else {
//process downlink burst
keystream = AtoBkeystream;
}
/* guard bits */
for (int i = 0; i < 3; i++) {
decrypted_data[i] = burst_binary[i];
}
//encrypt 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];
}
//encrypt 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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