refactor

encdec.py

@@ -1,51 +1,70 @@
 #!/usr/bin/env python3
 
+from itertools import cycle
 import os
 from pathlib import Path
-from itertools import cycle
-
 from sys import argv, stderr
 
 # Structure of pre-encoded payload
-# 8196    | 16        | ...     | 2   |
-# data D1 | version V | data D2 | crc |
+# 8196 | 16      | ...  | 2   |
+# data | version | data | crc |
 
 KEY = Path('./key.bin').read_bytes()
 
-D1_LEN = 8192
+V_OFFSET = 8192
 V_LEN = 16
+CRC_LEN = 2
+
+
+def eprint(*args, **kwargs):
+    print(*args, **kwargs, file=stderr)
+
 
 def xor(var, key):
     return bytes(a ^ b for a, b in zip(var, cycle(key)))
 
-def decrypt(data):
 
+def eprint_crc(crc):
+    eprint('crc:', ['0x%02x' % x for x in crc], f'{crc[0]*crc[1]}')
+
+
+def make_16yte_version(version):
+    return bytes([ord(c) for c in version] + [0] * (16 - len(version)))
+
+
+def decrypt(data):
     decr = xor(data, KEY)
     
-    d1 = decr[:D1_LEN]
-    v = decr[D1_LEN:D1_LEN+V_LEN]
-    d2 = decr[D1_LEN+V_LEN:-2]
-    crc = decr[-2:]
+    v = decr[V_OFFSET:V_OFFSET+V_LEN]
+    decr_data = decr[:-CRC_LEN]
+    crc = decr[-CRC_LEN:]
 
-    print('version:', v, file=stderr)
-    print('crc:', ['0x%02x' % x for x in crc], f'{crc[0]*crc[1]}', file=stderr)
+    eprint('version:', v)
+    eprint_crc(crc)
 
-    return d1 + d2
+    return decr_data
+
+
+def encrypt(data, version='2.01.19'):
+    v = make_16yte_version(version)
+    data = data[:V_OFFSET] + v + data[V_OFFSET+V_LEN:]
+    crc = b'\xd9\xab' # here will be some crc
+    
+    eprint('version:', v)
+    eprint_crc(crc)
+
+    return xor(data + crc, KEY)
 
-def encrypt(data, version='2.01.26'):
-    D1_LEN = 8192
-    v = bytes([ord(c) for c in version] + [0] * (16 - len(version)))
-    print('version:', v, file=stderr)
-    return xor(data[:D1_LEN] + v + data[D1_LEN:] + b'\xd8\x7f', KEY)
 
 def usage(info = None):
     if info:
-        print(info, file=stderr)
-    print(f'Usage: {argv[0]} <e|d> filename.bin > raw.bin', file=stderr)
-    print(f'  Example decode: {argv[0]} d k5_26_encrypted.bin > k5_26_raw.bin', file=stderr)
-    print(f'  Example encode: {argv[0]} e k5_26_raw.bin > k5_26_encrypted.bin', file=stderr)
+        eprint(info)
+    eprint(f'Usage: {argv[0]} <e|d> filename.bin > raw.bin')
+    eprint(f'  Example decode: {argv[0]} d k5_26_encrypted.bin > k5_26_raw.bin')
+    eprint(f'  Example encode: {argv[0]} e k5_26_raw.bin > k5_26_encrypted.bin')
     exit(128)
 
+
 def main():
     if len(argv) != 3:
         usage()
@@ -57,14 +76,15 @@ def main():
         encrypted = Path(fname).read_bytes()
         decrypted = decrypt(encrypted)
         os.write(1, bytes(decrypted))
-        print('Success!', file=stderr)
+        eprint('Success!')
         return
+
     if encdec == 'e':
-        print('WARNING! encoding not working for now, as CRC not valid', file=stderr)
+        eprint('WARNING! encoding not working for now, as CRC not valid')
         decrypted = Path(fname).read_bytes()
         encrypted = encrypt(decrypted)
         os.write(1, bytes(encrypted))
-        print('Success!', file=stderr)
+        eprint('Success!')
         return
 
     usage()