CTFtime: https://ctftime.org/event/2920h4

Author: xzhiyouu

Please don’t mind my broken English.

This is the first CTF I played with Flagaholic.
We got TOP 5 in the end.
There were a total of 1237 participating teams.
Thanks to my teammate and I
Final Scoreboard here~

I will write writeups for some interesting or guessy challenges.

[Misc] Dont Botherh3

This challenge was too guessy, so out of more than 1,200 teams, only 16 managed to solve it.

Here’s my solution.

The image is 512×512 and in RGB format. Most pixels share the same base color (64, 77, 205).

Some pixels have been increased by 2 in certain channels (only 0 or +2, never a decrease), so they differ slightly from the base color.

The image is divided into many small square blocks, and only those along the main diagonal contain these “+2 footprints.”

In each diagonal block, if you sum up all the “+2 occurrences” of its pixels, you get an integer.

That sequence of integers represents ASCII codes, which together form the flag.

Solution code~

from PIL import Image
import numpy as np

img = Image.open("chal.jpg").convert("RGB")
arr = np.array(img, dtype=np.uint8)
base = np.array([64, 77, 205], dtype=np.int32)

delta = arr.astype(np.int32) - base
steps = np.clip(delta, 0, None) // 2
steps = steps.sum(axis=2)

n = 32
h, w = steps.shape
bh, bw = h // n, w // n
codes = []
for i in range(n):
    block = steps[i*bh:(i+1)*bh, i*bw:(i+1)*bw]
    codes.append(block.sum())

flag = ''.join(chr(c) for c in codes).rstrip('\x00')
print(flag)
# v1t{c4nt_B3_both3r3d_vnkud1837}

GUESSY CHALL :>

[Misc] MOOOOh3

This is a cool challenge lol

You can find comment with COW programming language through exiftool.

After running the code, we got thismaybeapasswordbutwhoreallyknowsimjustmessginitisapassword

Do steghide to MOOOO.jpeg, and got TRYYY.txt there are many invisible spaces in the .txt file

Since I played SCIST Final CTF before, someone made a tool for solving this problem.

Got the flag v1t{D0wn_Th3_St3gN0_R4bb1t_H0l3}

[Forensics] Tryna crack?h3

This challenge also guessy, many people try to brute force the zip file password, but actually you can solve it with the tool “bkcrack”

I got quackquackquack.png after extracting challenge.zip.

After checking with exiftool, I found a comment that says password for zip file =)))) D4mn_br0_H0n3y_p07_7yp3_5h1d

BUT THE FLAG ISN’T v1t{D4mn_br0_H0n3y_p07_7yp3_5h1d}

lots of people are stuck here lol

I looked deeper and tried adjusting the image’s width and height, then got this.

The Morse code below translates to “SHA512.”

So it’s clear that the flag is supposed to be the SHA-512 of D4mn_br0_H0n3y_p07_7yp3_5h1d.

Got flag v1t{7083748baa3a42dc0a93811e4f5150e7ae1a050a0929f8c304f707c8c44fc95d86c476d11c9e56709edc30eba5f2d82396f426d93870b56b1a9573eaac8d0373}