picoCTF — Hide To See Write-Up

Challenge Overview

The challenge “Hide To See” is a steganography-based challenge in picoCTF where the goal is to extract hidden information from an image.

Steps to Solve:

Step 1: Downloading the Image

The challenge provides an image file. I first downloaded it using the given link in the picoCTF challenge portal.

Step 2: Steganography Analysis

Since the challenge title hinted at hidden data, I suspected steganography. One of the common tools for steganographic analysis is AperiSolve, an online tool designed to extract hidden files, messages, and metadata from images.

I uploaded the image to AperiSolve and analyzed the output. The tool successfully extracted a hidden text file named encrypted.txt.

Step 3: Inspecting encrypted.txt

I opened encrypted.txt, which contained an encoded or encrypted string. Since the challenge involved extracting hidden data, I suspected that the text was encoded using a simple cipher, such as Atbash, ROT13, or Base64 and as this challenge is on atbash cipher my first suspect is the atbash cipher.

ApriSolve

Step 4: Writing a Custom Python Script

To efficiently decode the text, I wrote a custom Python script to check for common encoding techniques:

def atbash_cipher(text):
    atbash_table = str.maketrans(
        "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz",
        "ZYXWVUTSRQPONMLKJIHGFEDCBAzyxwvutsrqponmlkjihgfedcba"
    )
    return text.translate(atbash_table)

# Encrypted text
ciphertext = "extracted_code from the encrypted.txt"

# Decrypt
plaintext = atbash_cipher(ciphertext)
print("Decrypted Text:", plaintext)

Step 5: Extracting the Flag

After running the script, I successfully retrieved the picoCTF flag from the decrypted text.

Decrypting

Flag: picoCTF{hidden_message} (example format)

Conclusion

This challenge demonstrated the importance of steganography tools like AperiSolve and basic cryptanalysis techniques such as Atbash and Base64 decoding. Writing a Python script to automate the decryption process made the challenge more efficient and helped quickly extract the flag.

This was a great exercise in steganography, encoding detection, and cryptography! 🔥