refactor

.gitignore

@@ -1 +1,2 @@
 fw/
+__pycache__/

base.py

@@ -0,0 +1,83 @@
+from itertools import cycle
+from pathlib import Path
+from sys import stderr
+
+from crctest import *
+
+# Structure of pre-encoded payload
+# 8196 | 16      | ...  | 2   |
+# data | version | data | crc |
+
+KEY = Path('./key.bin').read_bytes()
+
+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 eprint_crc(crc):
+    eprint('crc:', ['0x%02x' % x for x in crc], f'{crc[0]*crc[1]}')
+
+
+def make_16byte_version(version):
+    return bytes([ord(c) for c in version] + [0] * (16 - len(version)))
+
+
+def decrypt(data):
+    decr = xor(data, KEY)
+    
+    v = decr[V_OFFSET:V_OFFSET+V_LEN]
+    decr_data = decr[:-CRC_LEN]
+    crc = decr[-CRC_LEN:]
+
+    eprint('version:', v)
+    eprint_crc(crc)
+
+    return decr_data
+
+
+def encrypt(data, version='2.01.19'):
+    v = make_16byte_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 crctest(data):
+    decr = xor(data, KEY)
+    
+    v = decr[V_OFFSET:V_OFFSET+V_LEN]
+    decr_data = decr[:-CRC_LEN]
+    crc_dec = decr[-CRC_LEN:]
+    crc_enc = data[-CRC_LEN:]
+
+    eprint('version:', v)
+    eprint_crc(crc_dec)
+    eprint_crc(crc_enc)
+
+    crc1_test = crc_dec[0]*crc_dec[1]
+    crc2_test = crc_enc[0]*crc_enc[1]
+
+    for crc_f in [crc16_xmodem, crc16_buypass, crc16_ccitt_false, crc16_modbus]:
+        for d in [data[:-CRC_LEN], decr_data, decr_data[:V_OFFSET]+decr_data[V_OFFSET+V_LEN:-CRC_LEN], data[:V_OFFSET]+data[V_OFFSET+V_LEN:-CRC_LEN]]:
+            crc_try = crc_f(d)
+            eprint('try:', crc_try)
+            if crc_try == crc1_test:
+                eprint('BINGO: crc1_test', crc_try)
+                break
+            if crc_try == crc2_test:
+                eprint('BINGO: crc2_test', crc_try)
+                break
+
+    return decr_data

crctest.py

@@ -0,0 +1,58 @@
+
+# CRC-16/CCITT-FALSE
+def crc16_ccitt_false(data : bytearray):
+    offset = 0
+    length = len(data)
+    if data is None or offset < 0 or offset > len(data)- 1 and offset+length > len(data):
+        return 0
+    crc = 0xFFFF
+    for i in range(0, length):
+        crc ^= data[offset + i] << 8
+        for j in range(0,8):
+            if (crc & 0x8000) > 0:
+                crc =(crc << 1) ^ 0x1021
+            else:
+                crc = crc << 1
+    return crc & 0xFFFF
+
+# CRC-16/BUYPASS, CRC-16-ANSI, CRC-16-IBM
+def crc16_buypass(data: bytes):
+    xor_in = 0x0000  # initial value
+    xor_out = 0x0000  # final XOR value
+    poly = 0x8005  # generator polinom (normal form)
+    reg = xor_in
+    for octet in data:
+        # reflect in
+        for i in range(8):
+            topbit = reg & 0x8000
+            if octet & (0x80 >> i):
+                topbit ^= 0x8000
+            reg <<= 1
+            if topbit:
+                reg ^= poly
+        reg &= 0xFFFF
+        # reflect out
+    return reg ^ xor_out
+
+# https://docs.python.org/3/library/binascii.html
+import binascii
+def crc16_xmodem(data: bytes):
+  return binascii.crc_hqx(data, 0)
+
+def crc16_modbus(data : bytearray):
+    offset = 0
+    length = len(data)
+    if data is None or offset < 0 or offset > len(data) - 1 and offset + length > len(data):
+        return 0
+    crc = 0xFFFF
+    for i in range(length):
+        crc ^= data[offset + i]
+        for j in range(8):
+            if ((crc & 0x1) == 1):
+                crc = int((crc / 2)) ^ 40961
+            else:
+                crc = int(crc / 2)
+    return crc & 0xFFFF
+
+
+

encdec.py

@@ -1,59 +1,10 @@
 #!/usr/bin/env python3
 
-from itertools import cycle
 import os
 from pathlib import Path
-from sys import argv, stderr
+from sys import argv
 
-# Structure of pre-encoded payload
-# 8196 | 16      | ...  | 2   |
-# data | version | data | crc |
-
-KEY = Path('./key.bin').read_bytes()
-
-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 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)
-    
-    v = decr[V_OFFSET:V_OFFSET+V_LEN]
-    decr_data = decr[:-CRC_LEN]
-    crc = decr[-CRC_LEN:]
-
-    eprint('version:', v)
-    eprint_crc(crc)
-
-    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)
+from base import crctest, eprint, encrypt, decrypt
 
 
 def usage(info = None):
@@ -71,18 +22,21 @@ def main():
 
     encdec = argv[1]
     fname = argv[2]
+    file_bytes = Path(fname).read_bytes()
+    
+    if encdec == 'crc':
+        crctest(file_bytes)
+        return
 
     if encdec == 'd':
-        encrypted = Path(fname).read_bytes()
-        decrypted = decrypt(encrypted)
+        decrypted = decrypt(file_bytes)
         os.write(1, bytes(decrypted))
         eprint('Success!')
         return
 
     if encdec == 'e':
         eprint('WARNING! encoding not working for now, as CRC not valid')
-        decrypted = Path(fname).read_bytes()
-        encrypted = encrypt(decrypted)
+        encrypted = encrypt(file_bytes)
         os.write(1, bytes(encrypted))
         eprint('Success!')
         return