TryHackMe: c4ptur3-th3-fl4g Writeup

Overview

This writeup covers all four tasks of the "c4ptur3-th3-fl4g" CTF challenge on TryHackMe. Each task focuses on different cybersecurity and cryptography concepts.

---

Task 1: Encoding/Decoding

Objective: Decode various types of encoded messages to find flags.

Solutions

1. Leetspeak Decoding

Leetspeak (l33t sp34k) is internet slang where numbers and symbols replace similar-looking letters.

Challenge:

c4n y0u c4p7u23 7h3 f149?

Method: Look for number-to-letter substitutions:

• 4 looks like A
• 0 looks like O
• 1 looks like I or L
• 3 looks like mirrored E
• 7 looks like T
• 9 looks like g

Leetspeak Mapping:

0 = O     1 = I/L   3 = E     4 = A
5 = S     7 = T     8 = B     9 = G

Solution:

c4n y0u c4p7u23 7h3 f149?
can you capture the flag?

Answer: can you capture the flag?

Tools: Manual decoding with leetspeak chart, or CyberChef

---

2. Binary Decoding

Binary uses two digits (0 and 1) to represent data. Each 8 bits = 1 character.

Challenge:

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

Method:

Step 1: Split into 8-bit chunks
01101100 | 01100101 | 01110100 | ...

Step 2: Convert each to decimal
01101100 = 108
01100101 = 101
01110100 = 116

Step 3: Convert decimal to ASCII
108 = 'l'
101 = 'e'
116 = 't'

Answer: lets try some binary out!

Tools: CyberChef, Python, or manual conversion

---

3. Base32 Decoding

Base32 is an encoding scheme that represents binary data in a base-32 alphabet using 32 characters.

Challenge:

MJQXGZJTGIQGS4ZAON2XAZLSEBRW63LNN5XCA2LOEBBVIRRHOM======

Method: Use CyberChef or a Base32 decoder:

1. Paste the Base32 string
2. Decode to UTF-8
3. Read the output

Answer: base32 is super common in CTF's

Tools: CyberChef, Python (base64 module with Base32)

---

4. Base64 Decoding

Base64 is a binary-to-text encoding scheme. Each character represents 6 bits of data.

Challenge:

RWFjaCBCYXNlNjQgZGlnaXQgcmVwcmVzZW50cyBleGFjdGx5IDYgYml0cyBvZiBkYXRhLg==

Method:

1. Recognize Base64 (ends with = or ==)
2. Use CyberChef or echo command:

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

Tools: CyberChef, base64 command, Python

---

5. Hexadecimal Decoding

Hexadecimal (base 16) uses digits 0-9 and letters A-F.

Challenge:

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

Method: Convert hex pairs to ASCII:

68 = h
65 = e
78 = x
61 = a
...

Answer: hexadecimal or base16?

Tools: CyberChef, Python, or hex-to-ASCII converter

---

6. ROT13

ROT13 is a simple letter substitution cipher that replaces each letter with the letter 13 positions after it.

Challenge:

Ebgngr zr 13 cynprf!

Method: ROT13 is reciprocal - apply it twice to get the original.

Ebgngr zr 13 cynprf!
↓ (apply ROT13)
Rotate me 13 places!

Answer: Rotate me 13 places!

Tools: CyberChef (search "ROT13"), Python

---

7. ROT47 (Caesar Cipher Extended)

ROT47 is a variant of Caesar cipher that works on all printable ASCII characters (33-126), not just letters.

Challenge:

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

Method: ROT47 shifts all printable ASCII by 47 positions. Use CyberChef:

1. Search "ROT47"
2. Paste input
3. Read output

How ROT47 Works:

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

Tools: CyberChef, Python script

---

8. Morse Code

Morse code uses dots (·) and dashes (−) to represent letters and numbers.

Challenge:

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

Morse Code Chart:

A ·−    B −···  C −·−·  D −··   E ·     F ··−·  G −−·   H ····
I ··    J ·−−−  K −·−   L ·−··  M −−    N −·    O −−−   P ·−−·
Q −−·−  R ·−·   S ···   T −     U ··−   V ···−  W ·−−   X −··−
Y −·−−  Z −−··

Method: Split by spaces and decode each Morse pattern:

- = T
. = E
.-.. = L

Answer: TELECOMMUNICATION ENCODING

Tools: CyberChef, Morse decoder online, manual chart

---

9. Decimal/ASCII

Decimal representation of ASCII values.

Challenge:

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

Method: Convert decimal to ASCII:

85 = U
110 = n
112 = p
97 = a
99 = c
107 = k
32 = (space)
116 = t
...

Answer: Unpack this BCD

Tools: CyberChef, Python, ASCII table

---

Task 2: Spectrograms

Objective: Analyze an audio file's spectrogram to find hidden information.

File: secretaudio_1559007588454.wav (105,840 samples at 44100 Hz)

Concepts

• Spectrogram: Visual representation of frequency spectrum over time

  • X-axis: Time (seconds)
  • Y-axis: Frequency (Hz)
  • Color/Brightness: Signal intensity (dB - decibels)

• Sonogram/Voiceprint/Voicegram: Alternative names for audio spectrograms

• 3D Waterfall: Alternative 3D representation of spectrograms

Complete Python Solution

Use this proven Python script to generate spectrograms:

How to Use

Step 1: Save the script

Step 2: Run the script

Step 3: Output

[*] Loading audio file: secretaudio_1559007588454.wav
[+] Audio loaded: 105840 samples at 44100 Hz
[*] Generating spectrogram...
[+] Spectrogram saved as spectrogram.png
[✓] Spectrogram analysis complete!

Recommended Tools

• Sonic Visualiser (sonicvisualiser.org) - Best for spectrograms
• Audacity (audacityteam.org) - Built-in spectrogram view
• Python (scipy) - Programmatic analysis

---

Task 3: Steganography

Objective: Extract hidden data from JPEG images.

Files to Analyze:

• stegosteg_1559008553457.jpg - Contains hidden payload
• meme_1559010886025.jpg - Secondary image

Concepts

Steganography: Practice of concealing a file, message, image, or video within another file

• Key Difference: Data is hidden (steganography) vs scrambled (encryption)
• Common Methods:
  • Steghide (embeds in JPEG/WAV files)
  • LSB (Least Significant Bit) in images
  • Metadata/EXIF hiding
  • File concatenation
  • Invisible text/colors

Working Solution: Using Steghide

Step 1: Check for Hidden Data

Output:

"stegosteg_1559008553457.jpg":
  format: jpeg
  capacity: 2.5 KB
Try to get information about embedded data ? (y/n) y
Enter passphrase: 
  embedded file "steganopayload2248.txt":
    size: 13.0 Byte
    encrypted: rijndael-128, cbc
    compressed: yes

Step 2: Extract the Hidden File

When prompted:

Enter passphrase: 
(press Enter for no passphrase or leave empty)

Output:

wrote extracted data to "steganopayload2248.txt".

Step 3: View the Extracted Content

Output:

SpaghettiSteg%

Answer: SpaghettiSteg%

Pro Tips

✅ Try empty passphrase first (just press Enter)
✅ Check both JPG files for hidden data
✅ Use steghide info BEFORE extracting to see what's inside
✅ Look at file metadata with exiftool as first step
✅ If steghide fails, try LSB extraction tools (Stegsolve)
✅ Always check the file extension and format
✅ Some files may have multiple layers of steganography

---

Task 4: Security Through Obscurity

Objective: Find hidden data and text in files.

File: meme_1559010886025.jpg

Concept

Security Through Obscurity: Relying on secrecy of design/implementation as the main security method. Often considered weak when used alone - should be combined with actual encryption/security measures.

Solution: Using strings Command

Step 1: Extract Readable Text

Output:

Step 2: Identify the Hidden Data

From the strings output, you can see:

• Hidden message: AHH_YOU_FOUND_ME!

Answer: AHH_YOU_FOUND_ME!

Summary of All Answers

Task	Answer
Task 1.1	can you capture the flag?
Task 1.2	lets try some binary out!
Task 1.3	base32 is super common in CTF's
Task 1.4	Each Base64 digit represents exactly 6 bits of data.
Task 1.5	hexadecimal or base16?
Task 1.6	Rotate me 13 places!
Task 1.7	You spin me right round baby right round (47 times)
Task 1.8	TELECOMMUNICATION ENCODING
Task 1.9	Unpack this BCD
Task 2	(Hidden in spectrogram)
Task 3	SpaghettiSteg%
Task 4	AHH_YOU_FOUND_ME!