💀Bruh

53 Solves

Bruh...

Background Knowledge

Luckily, no background knowledge required for this challenge! Except, basic knowledge of Python programming and data types such as lists and dictionaries.

Solution

An encrypted flag and a bruh.py is given to the player.

bruh.py

char_map = {
    'a': 'z',
    'b': 'y',
    'c': 'x',
    'C': 'X',
    'd': 'w',
    'e': 'v',
    'f': 'u',
    'F': 'U',
    'g': 't',
    'h': 's',
    'i': 'r',
    'j': 'q',
    'k': 'p',
    'l': 'o',
    'm': 'n',
    'n': 'm',
    'o': 'l',
    'p': 'k',
    'q': 'j',
    'r': 'i',
    's': 'h',
    't': 'g',
    'T': 'G',
    'u': 'f',
    'v': 'e',
    'w': 'd',
    'x': 'c',
    'y': 'b',
    'z': 'a',
    '{': '{',
    '}': '}',
    ' ': 'cc',
    '!': 'dd',
    '?': 'ee',
    '.': 'ff',
    ',': 'gg',
    "'": 'hh',
    '"': 'ii',
    ':': 'jj',
    ';': 'kk',
    '-': 'll',
    '_': '_',
    '+': 'nn',
    '=': 'oo',
    '/': 'pp',
    '\\': 'qq',
    '|': 'rr',
    '1': '1',
    '0': '0',
}

def encrypt_text(text):
    encrypted_text = ''
    for c in text:
        encrypted_text += char_map[c]
    return encrypted_text

def generate_flag():
    flag = 'flag'
    return encrypt_text(flag)

So, it seems like there's a very interesting character mapping going on with the char_map dictionary.

You can decode this by hand, manually mapping each character to the correct letter, or you can copy paste the same list and remap it backwards!

solve.py

char_map = {
    'a': 'z',
    'b': 'y',
    'c': 'x',
    'C': 'X',
    'd': 'w',
    'e': 'v',
    'f': 'u',
    'F': 'U',
    'g': 't',
    'h': 's',
    'i': 'r',
    'j': 'q',
    'k': 'p',
    'l': 'o',
    'm': 'n',
    'n': 'm',
    'o': 'l',
    'p': 'k',
    'q': 'j',
    'r': 'i',
    's': 'h',
    't': 'g',
    'T': 'G',
    'u': 'f',
    'v': 'e',
    'w': 'd',
    'x': 'c',
    'y': 'b',
    'z': 'a',
    '{': '{',
    '}': '}',
    ' ': 'cc',
    '!': 'dd',
    '?': 'ee',
    '.': 'ff',
    ',': 'gg',
    "'": 'hh',
    '"': 'ii',
    ':': 'jj',
    ';': 'kk',
    '-': 'll',
    '_': '_',
    '+': 'nn',
    '=': 'oo',
    '/': 'pp',
    '\\': 'qq',
    '|': 'rr',
    '1': '1',
    '0': '0',
}

def decrypt_text(text: str):
    decrypted_text = ''
    while len(text) > 0:
        for k, v in char_map.items():
            if text.startswith(v):
                decrypted_text += k
                text = text[len(v):]
                break
    return decrypted_text

enc = "XGU101{dsb_wlvh_gsrh_xszoovmtv_vcrhg_yil}"
print(decrypt_text(enc))
# CTF101{why_does_this_challenge_exist_bro}