PicoCTF_2017: SoRandom

Category: Cryptography Points: 75 Description:

We found sorandom.py running at shell2017.picoctf.com:16768. It seems to be outputting the flag but randomizing all the characters first. Is there anyway to get back the original flag?


How random can computers be?


Firstly, it doesn't seem to be a random random.

$ nc shell2017.picoctf.com 16768
Unguessably Randomized Flag: BNZQ:449xg472190mwx6869b8pt10rwo92624

Looking in the sorandom.py code, we see that the random generator has already been preseeded!


Okay, let's crack our Python knuckles and get to work.

$ ./crack.py
FLAG: 107bd559693aef6692e1ed55ebe29514

Therefore, the flag is 107bd559693aef6692e1ed55ebe29514.