[CTF] DEFCON31 Quals

Welcome to Quals 

This challenge is probably a mic check. In the beginning, there was an issue where the server didn't work properly due to a high influx of users.

 

Anyway, I will explain this chall

 

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You can access the server of the problem through the provided URL. The problem was simple.

By using "ls /," it was possible to confirm the existence of "flag.txt" in the root directory, and reading it was all that needed to be done.

 

However, there was one issue here. When entering "ls /," it didn't provide the correct response.

I thought that it was being substituted (like Caesar cipher), so I had to transform the command accordingly

 

def rotate_string(s):
    rotation = 13 
    result = ""

    for char in s:
        if char.isalpha():
            ascii_offset = 97 if char.islower() else 65
            rotated = (ord(char) - ascii_offset + rotation) % 26 + ascii_offset
            result += chr(rotated)
        else:
            result += char

    return result

original_string = "cd / && cat welcome_flag.txt"
rotated_string = rotate_string(original_string)
print(rotated_string)

gotcha!!