scripts: support Sercomm crypto

Sercomm firmwares are encrypted with AES 256 CBC.
The key is generated with a custom algorithm from the firmware tag:
	char key[32];
	char version[32];
	char iv[32];
	char random[32];
	char size[32];
Key must be generated with Sercomm's algorithm. However, the rest of the
header can be empty. IV and random are set to 0 on purpose.

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>

diff --git a/scripts/sercomm-crypto.py b/scripts/sercomm-crypto.py
new file mode 100755 (executable)
index 0000000..bed3e49
--- /dev/null
+++ b/scripts/sercomm-crypto.py
@@ -0,0 +1,86 @@
+#!/usr/bin/env python3
+
+import argparse
+import binascii
+import hashlib
+import os
+import struct
+
+def create_header(key, version, iv, random, size):
+       header = struct.pack('32s32s32s32s32s', key, version, iv, random, size)
+
+       return header
+
+def create_output(args):
+       in_st = os.stat(args.input_file)
+       in_size = in_st.st_size
+
+       key = "".encode('ascii')
+       version = args.version.encode('ascii')
+       iv = "".encode('ascii')
+       random = "".encode('ascii')
+       size = str(in_size).encode('ascii')
+       header = create_header(key, version, iv, random, size)
+
+       out_f = open(args.output_file, 'w+b')
+       out_f.write(header)
+       out_f.close()
+
+       md5 = hashlib.md5()
+       md5.update(header[0x60:0x80])
+       md5.update(header[0x20:0x40])
+       md5_1 = md5.digest()
+
+       md5 = hashlib.md5()
+       md5.update(header[0x80:0xA0])
+       md5.update(header[0x20:0x40])
+       md5_2 = md5.digest()
+
+       key = md5_1 + md5_2
+
+       key_f = open(args.key_file, 'w+b')
+       key_f.write(binascii.hexlify(bytearray(key)))
+       key_f.close()
+
+       print("AES 256 CBC Key:", binascii.hexlify(bytearray(key)))
+
+def main():
+       global args
+
+       parser = argparse.ArgumentParser(description='')
+
+       parser.add_argument('--input-file',
+               dest='input_file',
+               action='store',
+               type=str,
+               help='Input file')
+
+       parser.add_argument('--key-file',
+               dest='key_file',
+               action='store',
+               type=str,
+               help='AES 256 CBC Key File')
+
+       parser.add_argument('--output-file',
+               dest='output_file',
+               action='store',
+               type=str,
+               help='Output file')
+
+       parser.add_argument('--version',
+               dest='version',
+               action='store',
+               type=str,
+               help='Version')
+
+       args = parser.parse_args()
+
+       if ((not args.input_file) or
+           (not args.key_file) or
+           (not args.output_file) or
+           (not args.version)):
+               parser.print_help()
+
+       create_output(args)
+
+main()