✅ MISCELLANEOUS - Babel

Writeup by: @goproslowyo

Tags

• medium

Files:

• babel

Description

Author: @JohnHammond

It’s babel! Just a bunch of gibberish, right? Download the file below.

Writeup

This was a C# file. We can look at the encoding function and reverse it. Here’s the reverse in python:

def reverse(txtstr, key='lQwSYRxgfBHqNucMsVonkpaTiteDhbXzLPyEWImKAdjZFCOvJGrU'):
    alphabet = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
    reversed_text = ""
    substitution_dict = dict()

    for i in range(len(alphabet)):
        substitution_dict[key[i]] = alphabet[i]

    for char in txtstr:
        if ('A' <= char <= 'Z') or ('a' <= char <= 'z'):
            reversed_text += substitution_dict[char]
        else:
            reversed_text += char

    return reversed_text

if __name__ == "__main__":
    print(reverse(encoded_str))

We can then run this, base64 decode the output, and grep for our flag:

 python rev.py| base64 -d | grep -a flag
flag{b6cfb6656ea0ac92849a06ead582456c}