Hacktober 2020 CTF - Trick or Treat

Oct 17, 2020

Challenge Description

We found a script being used by DEADFACE. It should be relatively straightforward, but no one here knows Python very well. Can you help us find the flag in this Python file?

Solution

On this chalange, we where given a simple Python program source code:

from hashlib import md5 as m5

def show_flag():
    b = 'gginmevesogithoooedtatefadwecvhgghu' \
        'idiueewrtsadgxcnvvcxzgkjasywpojjsgq' \
        'uegtnxmzbajdu'
    c = f"{b[10:12]}{b[6:8]}{b[4:6]}{b[8:10]}" \
        f"{b[4:6]}{b[12:14]}{b[2:4]}{b[0:2]}" \
        f"{b[14:16]}{b[18:20]}{b[16:18]}{b[20:22]}"
    m = m5()
    m.update(c.encode('utf-8'))
    d = m.hexdigest()
    return f"flag{{{d}}}"

def show_msg():
    print(f'Smell my feet.')

show_msg()

We instantly concluded that we need to execute the show_flag() function rather than the show_msg() function, with a print() Function

from hashlib import md5 as m5

def show_flag():
    b = 'gginmevesogithoooedtatefadwecvhgghu' \
        'idiueewrtsadgxcnvvcxzgkjasywpojjsgq' \
        'uegtnxmzbajdu'
    c = f"{b[10:12]}{b[6:8]}{b[4:6]}{b[8:10]}" \
        f"{b[4:6]}{b[12:14]}{b[2:4]}{b[0:2]}" \
        f"{b[14:16]}{b[18:20]}{b[16:18]}{b[20:22]}"
    m = m5()
    m.update(c.encode('utf-8'))
    d = m.hexdigest()
    return f"flag{{{d}}}"

def show_msg():
    print(f'Smell my feet.')

#show_msg()
print(show_flag())

Running the modified code again, give us the flag:

m3dsec@local:~/ht/prog/02_Trick_or_Treat$ python3 trickortreat.py
flag{2f3ba6b5fb8bb84c33b584f981c2d13d}

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