Reverse Engineering Python Flag Encryption Script

Reverse Engineering Python Flag Encryption Script

This article explores the process of reverse engineering a Python script that encrypts a flag using a simple XOR and bit-shifting algorithm. The script utilizes a specific pattern to manipulate the flag before outputting the final encrypted result. We'll break down the code, decipher the encrypted flag, and provide the solution script.

The Encrypted Flag

The challenge presents us with an encrypted flag in the form of a decimal integer. Our goal is to recover the original flag, which is hidden within this numerical representation.

Understanding the Encryption Script

The provided script implements a custom encryption algorithm that iteratively manipulates the flag. Here's a breakdown:

1. Reversal: The flag is initially reversed (flag = flag[::-1]).
2. Iterative XOR and Shifting: The script iterates through each character in the reversed flag, performing XOR and bit-shifting operations on adjacent characters. This process involves:
   • Ord Conversion: Converting each character to its ASCII value (ord(flag[i])).
   • XOR and Shifting: Applying XOR and bit-shifting operations with specific offsets.
   • Result Accumulation: Combining the results from each iteration into a final result variable.
3. Output: The script outputs the final result, which is the encrypted flag.

Deciphering the Flag

To decrypt the flag, we need to reverse the encryption steps. This involves:

1. Converting to Hexadecimal: The decimal result is converted to its hexadecimal representation.
2. Decoding ASCII: Each pair of hexadecimal characters is converted back to its ASCII value, forming the original flag characters.
3. Reverse the Reversal: Since the flag was initially reversed, we need to reverse it again to obtain the final solution.

Solution Script

The following Python script demonstrates the decryption process:

result = 591620785604527668617886
hex_result = hex(result)[2:] # Remove '0x' prefix
flag = ''
for i in range(0, len(hex_result), 2):
    ascii_code = int(hex_result[i:i+2], 16) # Convert hex to decimal
    flag += chr(ascii_code)
flag = flag[::-1] # Reverse the initial reversal
print(flag)

The Solution

Running the solution script reveals the original flag: flag{s1mpl3_r3v3rs1ng}. This demonstrates the success of reverse engineering the encryption algorithm and recovering the hidden message.

Key Takeaways

This exercise highlights the importance of understanding encryption techniques and the potential for reversing them. While simple algorithms can be easily deciphered, more complex methods often require advanced tools and techniques. Learning about these concepts is essential for working with cybersecurity and protecting sensitive data.