c4ptur3-th3-fl4g

Summary

c4ptur3-th3-fl4g is the seventh machine of the Road to eJPTv2 series and the most different one so far. No service exploitation, no reverse shells, no privesc. It’s a pure encoding, cryptography and steganography challenge — designed to get you comfortable with data representation systems that appear constantly in CTFs and forensic analysis.

This room covers: leetspeak, binary, Base32, Base64, hexadecimal, ROT13, ROT47, Morse code, BCD, Brainfuck/Malbolge, audio spectrograms and image steganography.

🎥 Video Walkthrough

If you prefer to follow the walkthrough step by step, keep reading. The video covers the same process in visual format.

Tools Used

• CyberChef — swiss army knife for encoding/decoding
• Audacity — spectrogram visualization
• steghide — extracting hidden data from images
• binwalk — analysis of composite files

Solution Overview

This room is divided into four sections:

1. Translations & Shifting — 10 encoding/decoding challenges
2. Spectrograms — hidden message in audio frequencies
3. Steganography — data hidden inside an image
4. Security through obscurity — file inside another file

Section 1: Translations & Shifting

This section presents 10 encoded strings that need to be decoded. The main tool is CyberChef (https://gchq.github.io/CyberChef/), which allows applying multiple transformations in a chain.

Challenge 1: Leetspeak

c4n y0u c4p7u23 7h3 f149?

Leetspeak (l33tspeak) is a substitution of letters with visually similar numbers or symbols. Common in hacker culture since the 80s.

Answer: can you capture the flag?

Challenge 2: Binary

01101100 01100101 01110100 01110011 00100000 01110100 01110010 01111001 00100000 01110011 01101111 01101101 01100101 00100000 01100010 01101001 01101110 01100001 01110010 01111001 00100000 01101111 01110101 01110100 00100001

Each group of 8 bits represents an ASCII character. In CyberChef: From Binary.

Answer: lets try some binary out!

Challenge 3: Base32

MJQXGZJTGIQGS4ZAON2XAZLSEBRW63LNN5XCA2LOEBBVIRRHOM======

Base32 uses the A-Z and 2-7 alphabet, with = as padding. In CyberChef: From Base32.

Answer: base32 is super common in CTF's

Challenge 4: Base64

RWFjaCBCYXNlNjQgZGlnaXQgcmVwcmVzZW50cyBleGFjdGx5IDYgYml0cyBvZiBkYXRhLg==

Base64 uses A-Z, a-z, 0-9, +, / and = as padding. Recognizable by the == at the end. In CyberChef: From Base64.

Answer: Each Base64 digit represents exactly 6 bits of data.

Challenge 5: Hexadecimal

68 65 78 61 64 65 63 69 6d 61 6c 20 6f 72 20 62 61 73 65 31 36 3f

Each hex pair represents one byte. 20 is the space character in ASCII. In CyberChef: From Hex.

Answer: hexadecimal or base16?

Challenge 6: ROT13

Ebgngr zr 13 cynprf!

ROT13 shifts each letter 13 positions in the alphabet. Applied twice it returns to the original (it is its own inverse). In CyberChef: ROT13.

Answer: Rotate me 13 places!

Challenge 7: ROT47

*@F DA:? >6 C:89E C@F?5 323J C:89E C@F?5 Wcf E:>6DX

ROT47 is like ROT13 but applies to 94 printable ASCII characters (from 33 to 126), not just letters. That’s why it can encrypt symbols, numbers and letters. In CyberChef: ROT47.

Answer: You spin me right round baby right round (47 times)

Challenge 8: Morse Code

. .-.. . -.-. --- -- -- ..- -. .. -.-. .- - .. --- -.
. -. -.-. --- -.. .. -. --.

Morse code uses dots and dashes to represent letters. In CyberChef: From Morse Code.

Answer: TELECOMMUNICATION ENCODING

Challenge 9: BCD (Binary Coded Decimal)

85 110 112 97 99 107 32 116 104 105 115 32 66 67 68

BCD represents each decimal digit with its bit equivalent. These values are directly decimal ASCII codes. In CyberChef: From Charcode (decimal base).

Answer: Unpack this BCD

Challenge 10: Multi-layer string

LS0tLS0gLi0tLS0g...

This string requires decoding in multiple layers:

1. Base64 → produces Morse code
2. Morse → produces plain text

In CyberChef: From Base64 → From Morse Code.

Answer: Let's make this a bit trickier...

Section 2: Spectrograms

A spectrogram is a visual representation of the frequencies of an audio signal over time. Messages can be hidden in audio by setting the volume of specific frequencies to form letters or images when viewed in a spectrogram.

Process

1. Download the audio file from the room
2. Open it in Audacity
3. In the audio track, click on the track name → select “Spectrogram”
4. The spectrogram will reveal text visible in the frequencies

Answer: Super Secret Message

Section 3: Steganography

Steganography hides information inside other files — images, audio, video — in a way that is not visible to the naked eye. Unlike cryptography (which encrypts the message), steganography hides the existence of the message.

Process

1. Download the image from the room
2. Use steghide to extract hidden data:

steghide extract -sf image.jpg

3. If it has a passphrase, try with an empty string (press Enter without typing anything)
4. The extracted file contains the answer

Answer: SpaghettiSteg

Section 4: Security through obscurity

This section shows how attackers (and defenders) can hide files inside other files — a technique used in both malware and CTFs.

Challenge 1: File inside a file

1. Download the file from the room
2. Use binwalk to see what’s inside:

binwalk file

3. Extract the content:

binwalk -e file

4. Inside you will find the hidden file

First hidden file: hackerchat.png

Challenge 2: Hidden text inside the file

1. With the extracted file, inspect it:

strings hackerchat.png

Or open it with a hex editor and look for plain text at the end of the file.

Hidden text: AHH_YOU_FOUND_ME!

Quick Encoding Reference

This table summarizes the most common encodings in CTFs:

Lessons Learned

• CyberChef is indispensable for CTFs — Most of the encodings in this room are solved in seconds with CyberChef. Learning to chain operations in CyberChef is a fundamental skill for any CTF player.
• Recognizing encodings at a glance saves time — == at the end → Base64. Uppercase with 2-7 → Base32. Dots and dashes → Morse. 0s and 1s in groups of 8 → Binary. Building this visual recognition is essential.
• Steganography isn’t just images — Information can be hidden in audio (spectrograms), video, PDF documents, ZIP files, and more. Whenever you have a file in a CTF, ask yourself: is there something hidden here?
• binwalk and strings are your first commands with unknown files — strings shows readable text inside any binary file. binwalk detects embedded files. Use them before opening any suspicious file.
• Security through obscurity is not real security — Hiding files inside others or changing extensions does not protect data. An attacker with binwalk or strings finds it in seconds. Real security requires encryption, not concealment.

For the eJPT

Although the eJPT focuses more on network and system exploitation, the concepts from this room are relevant for:

• Recognizing encoded data in web application responses (Base64 in cookies, JWT tokens, etc.)
• Basic forensic analysis in post-exploitation
• Understanding how information is hidden in files

Approximate completion time: 30-45 minutes with CyberChef open and the encoding reference at hand.

References

• c4ptur3-th3-fl4g — TryHackMe
• CyberChef — GCHQ
• Audacity
• steghide documentation
• binwalk documentation
• GTFOBins