Add Ki recovery from eKi and fix OPC return type

README.md

@@ -41,6 +41,7 @@ Options:
   -o OP, --op=OP              32 char OP key
   -t TRANS, --transport=TRANS 32 char Transport key
   -k KI, --ki=KI              Optional 32 char Ki key (to avoid random generation)
+  -e EKI, --eki=EKI           32 char eKI key (to recover Ki)
 
 $ kiopcgen  -o D7DECB1F50404CC29ECBF989FE73AFC5 -t 2257CC6E9746434B89F346F0276CCAEC
 {'KI': '780E6AC95A2E43449C15BDCDD0450982',
@@ -51,6 +52,13 @@ $ kiopcgen -o D7DECB1F50404CC29ECBF989FE73AFC5 -t 2257CC6E9746434B89F346F0276CCA
 {'KI': '8978B79E7C104F678FA5C336509DB188',
  'OPC': '6F2E82855DEE7C893CB1F7A72FD08B57',
  'eKI': 'FBE8C170F6A5C6C257E5324719674818'}
+
+Or recover Ki from an encrypted eKi:
+
+$ kiopcgen -o D7DECB1F50404CC29ECBF989FE73AFC5 -t 2257CC6E9746434B89F346F0276CCAEC -e 4601138387FCF7D666ED24BBB3EE37B8
+{'KI': '780E6AC95A2E43449C15BDCDD0450982',
+ 'OPC': '2274B84B8043105A28AABBE53EF1D014',
+ 'eKI': '4601138387FCF7D666ED24BBB3EE37B8'}
 ```
 
 Or import the kiopcgenerator module to use in your scripts
@@ -72,6 +80,10 @@ print (kiopcgenerator.gen_eki(transport, ki))
 # 8FAC9FE22D306EA4CB86279B3473D8CB
 print (kiopcgenerator.gen_opc_eki(op, transport, ki))
 # {'KI': 'EBD77DF6CFF949448ACF82B8FE4E59E3', 'eKI': '8FAC9FE22D306EA4CB86279B3473D8CB', 'OPC': '33244F04A86408A53110D1FCAFD04288'}
+
+# Recover Ki from eKi
+print (kiopcgenerator.recover_ki(op, transport, eki))
+# {'KI': 'EBD77DF6CFF949448ACF82B8FE4E59E3', 'eKI': '8FAC9FE22D306EA4CB86279B3473D8CB', 'OPC': '33244F04A86408A53110D1FCAFD04288'}
 ```
 
 ## Installation

kiopcgen

@@ -17,9 +17,14 @@ parser = OptionParser()
 parser.add_option("-o", "--op", dest="op", help="32 char OP key")
 parser.add_option("-t", "--transport", dest="trans", help="32 char Transport key")
 parser.add_option("-k", "--ki", dest="ki", help="Optional 32 char Ki key (to avoid random generation)")
+parser.add_option("-e", "--eki", dest="eki", help="32 char eKI key (to recover Ki)")
 (options, args) = parser.parse_args()
 
-if options.op and options.trans:
+if options.eki and options.trans and options.op:
+    result = kiopcgenerator.recover_ki(options.op, options.trans, options.eki)
+    pprint.pprint(result)
+    sys.exit(0)
+elif options.op and options.trans:
     if not options.ki:
         options.ki = kiopcgenerator.gen_ki()
 

kiopcgenerator/lib.py

@@ -45,7 +45,7 @@ def calc_opc_hex(self, k_hex, op_hex=None):
         aes_crypt = AES.new(ki, mode=AES.MODE_CBC, IV=iv)
         data = op
         o_pc = self._xor_str(data, aes_crypt.encrypt(data))
-        return binascii.hexlify(o_pc)
+        return binascii.hexlify(o_pc).decode('utf-8')
 
     def _xor_str(self, s, t):
         """xor two strings together"""
@@ -79,12 +79,31 @@ def gen_opc(op, ki):
     return hss.calc_opc_hex(ki, op).upper()
 
 
+def aes_128_cbc_decrypt(key, ciphertext):
+    """
+    implements aes 128b decryption with cbc.
+    """
+    keyb = binascii.unhexlify(key)
+    ciphertextb = binascii.unhexlify(ciphertext)
+    decryptor = AES.new(keyb, AES.MODE_CBC, IV=IV)
+    plaintext = decryptor.decrypt(ciphertextb)
+    return plaintext.hex().upper()
+
+
 def gen_eki(transport, ki):
     """
     generates eKI based on ki and transport key
     """
     return aes_128_cbc_encrypt(transport, ki)
 
 
+def recover_ki(op, transport, eki):
+    """
+    recovers ki from eKI and generates opc using the transport key and op
+    """
+    ki = aes_128_cbc_decrypt(transport, eki)
+    return {"KI": ki, "OPC": gen_opc(op, ki), "eKI": eki}
+
+
 def gen_opc_eki(op, transport, ki):
     return {"KI": ki, "OPC": gen_opc(op, ki), "eKI": gen_eki(transport, ki)}