Code Pyn

98B

bruteforcePYC.py

569B

pyn.pyc

4KB

return.txt

Category: Reverse - Points: 34 - Solves: 20 Description: I lost my pin code. Can you help me find it?

Infos:

A .pyc file is provided (pyn.pyc)

Solution: To solve this challenge you need to find a solution to decrypt the .pyc file or to recover the program code. To do this I chose to develop a little python script (bruteforcePYC.py). The script recove the program structure and we can see what he is doing. For example the python script return this :

  8          24 LOAD_NAME                4 (len)
             26 LOAD_NAME                3 (pin)
             28 CALL_FUNCTION            1
             30 LOAD_CONST               5 (4)

This block indicate that the PIN is composed by 4 digits (LOAD_CONST (4)) After theses lines indicate that we need to do a XOR between 5 and 3 :

60 LOAD_CONST               6 (5)
62 BINARY_XOR
64 LOAD_CONST               7 (3)

And it's the same for the 2 following PIN

86 LOAD_CONST               7 (3)
88 BINARY_XOR
90 LOAD_CONST               6 (5)

112 LOAD_CONST              10 (8)
114 BINARY_XOR
116 LOAD_CONST               8 (1)

So we have the 3 first digits (669) and the fourth need to be find manually. When we test the last digit, we found speedly that is 1. So we know the PIN code : 6691 and the FLAG is the PIN so...

🚩 FLAG

DVC{6691}