tools: add the shownas tool

tools/pycrate_shownas.py

@@ -0,0 +1,72 @@
+#!/usr/bin/env python3
+
+# -*- coding: UTF-8 -*-
+#/**
+# * Software Name : pycrate
+# * Version : 0.4
+# *
+# * Copyright 2020. Benoit Michau. P1Sec.
+# *
+# * This program is free software: you can redistribute it and/or modify
+# * it under the terms of the GNU General Public License version 2 as published
+# * by the Free Software Foundation. 
+# *
+# * This program 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 will find a copy of the terms and conditions of the GNU General Public
+# * License version 2 in the "license.txt" file or
+# * see http://www.gnu.org/licenses/ or write to the Free Software Foundation,
+# * Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA
+# *
+# *--------------------------------------------------------
+# * File Name : pycrate_shownas.py
+# * Created : 2020-12-08
+# * Authors : Benoit Michau 
+# *--------------------------------------------------------
+#*/
+
+import os
+import sys
+import argparse
+
+from binascii       import unhexlify, hexlify
+from pycrate_mobile import NAS
+
+
+def main():
+    #
+    parser = argparse.ArgumentParser(description='decode and pretty print mobile 2G-3G-4G-5G NAS message')
+    parser.add_argument('NASPDU', type=str, help='hexadecimal encoded NAS message')
+    parser.add_argument('-mt', action='store_true', help='force decoding to Mobile Terminated NAS message')
+    parser.add_argument('-mo', action='store_true', help='force decoding to Mobile Originated NAS message')
+    parser.add_argument('-l2', action='store_true', help='message includes a GSM L2 pseudo-length header')
+    args = parser.parse_args()
+    #
+    try:
+        buf = unhexlify(args.NASPDU)
+    except Exception as err:
+        print('[+] invalid hexadecimal NAS message, error: %s' % err)
+        return 0
+    #
+    if args.mt:
+        msg, err = NAS.parse_NAS_MT(buf, args.l2)
+    elif args.mo:
+        msg, err = NAS.parse_NAS_MO(buf, args.l2)
+    else:
+        msg, err = NAS.parse_NAS_MT(buf, args.l2)
+        if err:
+            msg, err = NAS.parse_NAS_MO(buf, args.l2)
+    #
+    if err:
+        print('[+] unable to decode the provided NAS message')
+    else:
+        print('[+] decoded NAS message:\n%s' % msg.show())
+    return 0
+
+
+if __name__ == '__main__':
+    sys.exit(main())
+