Cat code (3 points)

Ahoy, officer,

due to the lack of developers on board, the development of the access code generator for the satellite connection was entrusted to the cat of the chief officer. Your task is to analyze the cat's creation and find out the code.

May you have fair winds and following seas!

Download the cat code. (MD5 checksum: aac150b3f24e5b047ee99e25ad263f56)

Hints

• Cats are cute and all, but studies have shown that they really aren't good developers.

Solution

After extracting the files with python source code we see (in meoemeow.py) that the program runs in a loop asking for user input until the user acknowledges that kittens rule the world. Then two imported functions from meow.py are executed.

After closer examination of meow.py we come across the following code:

UNITE = 1
UNITED = 2


def meow(kittens_of_the_world):
    """
    meowwwwww meow
    """
    print('meowwww ', end='')
    if kittens_of_the_world < UNITED:
        return kittens_of_the_world
    return meow(kittens_of_the_world - UNITE) + meow(kittens_of_the_world - UNITED)

This is a naive implementation of calculating n-th member of the Fibonacci sequence which is used as an example of poorly used recursion in almost all textbooks. Let's replace it by a non-recursive version, e.g. like this:

def meow(kittens_of_the_world):
    if kittens_of_the_world < UNITED:
        return kittens_of_the_world
    prev = 0
    cur = 1
    n = 1
    while n < kittens_of_the_world:
        nxt = cur + prev
        prev = cur
        cur = nxt
        n += 1
    return cur

If we don't mind the meowing we can just run it to get the flag. If we do, we can also remove the line containing print('meowwww ', end='') in meowmeow(meow) function.

$ python meowmeow.py
Who rules the world? kittens
FLAG{YcbS-IAbQ-KHRE-BTNR}