1 files changed, 138 insertions, 0 deletions
diff --git a/lib/decryption/decryption_impl.cc b/lib/decryption/decryption_impl.cc
new file mode 100644
index 0000000..4347b62
--- /dev/null
+++ b/lib/decryption/decryption_impl.cc
@@ -0,0 +1,138 @@
+/* -*- 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/endian.h>
+#include <grgsm/gsmtap.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[15];
+            uint8_t BtoAkeystream[15];
+            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) & 0x3fff;
+            bool uplink_burst = (be32toh(header->frame_number) & 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);
+            run(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];
+            }
+            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];
+            }
+            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 */
+