From 7f1250a7fea716a13c1678a14dbc417ff57e461f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=81lvaro=20Fern=C3=A1ndez=20Rojas?= <noltari@gmail.com>
Date: Tue, 2 Jun 2020 08:37:54 +0200
Subject: [PATCH] scripts: support Sercomm crypto
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

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>
---
 scripts/sercomm-crypto.py | 86 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 86 insertions(+)
 create mode 100755 scripts/sercomm-crypto.py

diff --git a/scripts/sercomm-crypto.py b/scripts/sercomm-crypto.py
new file mode 100755
index 0000000000..bed3e494b6
--- /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()