Deep Fried Data - Misc

Points: 465 | Flag: 0xfun{d33p_fr13d_3nc0d1ng_0n10n} | Solved by: Smothy @ 0xN1umb

what we got

a single file notes.txt that file says is gzip compressed. challenge description says "if you fry something enough times, it becomes unrecognizable" so we're looking at layers of encoding/compression stacked on top of each other like a cursed onion

the solve

ran file on it - gzip. decompressed it - zlib inside. decompressed that - base64. and it just kept going lmao

wrote a python script to recursively detect and decode:

import gzip, bz2, lzma, zlib, base64
import string

data = open('notes.txt', 'rb').read()

while True:
    if data[:2] == b'\x1f\x8b':          # gzip
        data = gzip.decompress(data)
    elif data[:2] in (b'\x78\x9c', b'\x78\x01', b'\x78\xda'):  # zlib
        data = zlib.decompress(data)
    elif data[:3] == b'BZh':             # bzip2
        data = bz2.decompress(data)
    else:
        text = data.decode('ascii').strip()
        charset = set(text)

        if text.startswith('<~'):         # ascii85
            data = base64.a85decode(text[2:text.rindex('~>')])
        elif charset.issubset(set('ABCDEFGHIJKLMNOPQRSTUVWXYZ234567=')):  # base32
            data = base64.b32decode(text)
        elif charset.issubset(set('0123456789abcdefABCDEF')):  # hex
            data = bytes.fromhex(text)
        else:                             # base64
            data = base64.b64decode(text)

    if b'0xfun{' in data and b'keep_decoding' not in data:
        break

the encoding layers used (132+ rounds total):

• gzip compression
• zlib compression
• base64 encoding
• base32 encoding
• hex encoding
• ascii85 encoding

all mixed together in random order. truly deep fried fr

at round ~87 there's a troll fake flag: 0xfun{lol_not_yet_keep_decoding} followed by REAL_DATA_FOLLOWS: and more encoded data. had to strip that and keep going for another ~45 rounds of base64 until the real flag dropped

flag

0xfun{d33p_fr13d_3nc0d1ng_0n10n}

the name makes sense now - deep fried encoding, peeled like an onion. 132 layers of compression and encoding. absolute madness

smothy out ✌️