AceCTF

Achieved Rank 2 🥈

Name	Category	Solved?
Tabs&Spaces	Steganography	✅
Cryptic Pixels	Steganography	✅
Whispering Waves	Steganography	✅
The Mysterious Building	OSINT	✅

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Steganography

Tabs&Spaces

A mysterious ZIP file containing a collection of images and a file has been discovered. The task is to retrieve the flag.

We’re given a zip file that contains a random python file and a ctf folder that contains a lot of jpg file.

Noticed that the name of the files have spaces before the number

I decided to rename the files so the name of the file can appear when I use the command ls

since it’s related to steganography, I decided to check all the metadatas of the images and noticed that there’s a lot of png files that are using jpg extension but only one true jpg file, that is 87.jpg

let’s try to find something using stegseek to 87.jpg

whitespace_flag.txt

After checking it out, apparently we can’t use stegsnow to solve it, but let’s try decoding it to binary where \t is 1 and ' ' is 0

command: cat whitespace_flag.txt | tr ' ' '0' | tr '\t' '1'

Output

01000001
01000011
01000101
01000011
01010100
01000110
01111011
01101110
00110000
01011111
00110011
01111000
01110000
00110001
00110000
00110001
00110111
01011111
01101110
00110000
01011111
01100111
00110100
00110001
01101110
01111101

Put it into cyberchef and we got the flag

Flag: ACECTF{n0_3xp1017_n0_g41n}

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Cryptic Pixels

This image looks normal at first, but something important is hidden inside. The secret is carefully concealed, making it hard to find.

Your task is to explore the image, uncover the hidden message, and reveal what’s concealed. Do you have what it takes to crack the code and unlock the secret?

Submit your answer in the following format: ACECTF{3x4mpl3\_fl4g}

We’re given a zip file containing an png image. Based on the description, there’s a couple methods we can use.

The methods are using:

• Stegseek/Steghide
• Foremost/Binwalk

Since we didn’t get anything from using stegseek/steghide, let’s try using binwalk instead

Command: binwalk CrypticPixels.png

Output

DECIMAL       HEXADECIMAL     DESCRIPTION
--------------------------------------------------------------------------------
0             0x0             PNG image, 1600 x 1080, 8-bit/color RGBA, non-interlaced
91            0x5B            Zlib compressed data, compressed

WARNING: Extractor.execute failed to run external extractor 'jar xvf '%e'': [Errno 2] No such file or directory: 'jar', 'jar xvf '%e'' might not be installed correctly
753923        0xB8103         Zip archive data, encrypted at least v1.0 to extract, compressed size: 38, uncompressed size: 26, name: flag.txt
754121        0xB81C9         End of Zip archive, footer length: 22

To extract a flag from a password-protected zip file, use zip2john to create a hash of the file, then use john to crack

John Command

zip2john B8103.zip > hash.txt
john hash.txt

Output

Using default input encoding: UTF-8
Loaded 1 password hash (PKZIP [32/64])
Will run 8 OpenMP threads
Press 'q' or Ctrl-C to abort, almost any other key for status
qwertyuiop       (B8103.zip/flag.txt)     
1g 0:00:00:00 DONE (2025-02-28 08:01) 33.33g/s 4369Kp/s 4369Kc/s 4369KC/s 123456..kovacs
Use the "--show" option to display all of the cracked passwords reliably
Session completed.

flag.txt

JLNLCO{q4q4_h0d'a3_5v4a7}

There are two possibilities: the flag is encoded using either ROT13 or ROT47. Let’s use CyberChef’s ROT13 Brute Force tool to identify the

ROT13 Bruteforce

and we get the flag at Amount = 17

Flag: ACECTF{h4h4_y0u'r3_5m4r7}

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Whispering Waves

Alex, a passionate linguist and culture enthusiast, frequently visits the website Francophonie.org to learn about the French-speaking world. Alex is known for their love of cryptography and steganography, often hiding messages in unsuspecting places.

We’re given a set of wordlist and zip file that is protected with a password. I suspect that the zip file can be cracked using the wordlist given by the challenge, and yes it can. the password is Vierges

The zip contains a wav file. If we analyzed it using Sonic Visualizer and enable spectogram layer.

bottom means 0 and top means 1, collect all the data and if it is decoded using binary then we will get the flag

Flag: ACECTF{53cur1n6w3b}

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OSINT

The Mysterious Building

We’re given an image where it looks like some kind of building with a tower near it. we assume that it’s in India after checking the metadata of the image using exiftool.

Exiftool Output

ExifTool Version Number         : 12.57
File Name                       : OSINT-1.jpg
Directory                       : .
File Size                       : 255 kB
File Modification Date/Time     : 2025:02:27 19:05:17+07:00
File Access Date/Time           : 2025:02:27 19:17:39+07:00
File Inode Change Date/Time     : 2025:02:27 19:05:17+07:00
File Permissions                : -rwxrwxrwx
File Type                       : JPEG
File Type Extension             : jpg
MIME Type                       : image/jpeg
JFIF Version                    : 1.01
Resolution Unit                 : inches
X Resolution                    : 96
Y Resolution                    : 96
XMP Toolkit                     : Image::ExifTool 13.10
Description                     : National Capital of India
Author                          : Описание соответствует действительности
Comment                         : Определенно не Россия
Image Width                     : 734
Image Height                    : 858
Encoding Process                : Baseline DCT, Huffman coding
Bits Per Sample                 : 8
Color Components                : 3
Y Cb Cr Sub Sampling            : YCbCr4:2:0 (2 2)
Image Size                      : 734x858
Megapixels                      : 0.630

My team member said that it’s the Pitampura TV Tower. After checking it using google maps, it’s right and the building should be near that tower.

By using the logo on the building, we found the exact building

PP Trade Centre

and the name of the building is PP Trade Centre

Flag: ACECTF{pp_trade_centre}