interencdec picoCTF2024

Summary

The article provides a step-by-step solution to a cryptography challenge from picoCTF2024, involving decoding a base64 string multiple times and using a Caesar cipher to reveal the final flag.

Abstract

The author of the article is actively participating in the picoCTF2024 event and has chosen to document an interesting challenge from the Cryptography category. The challenge involves decoding a file to uncover its true meaning. After downloading the file, the author discovers a base64 encoded string which, when decoded, reveals another layer of base64 encoding. Upon further decoding and removing extraneous characters, a string resembling a flag is found, but it is still encrypted using a Caesar cipher. The author uses an online tool to decode the Caesar cipher, revealing the final flag. The article concludes with an invitation for readers to explore more solutions on the author's GitHub repository and encourages feedback and interaction.

Opinions

The author finds the cryptography challenge engaging and worth sharing.
Decoding processes are emphasized as important for solving such challenges.
The author suggests that multiple layers of encoding may be present in such challenges, hinting at the complexity of the task.
The use of an online tool for decoding the Caesar cipher indicates the author's pragmatic approach to problem-solving.
The author values community engagement and encourages readers to interact by asking questions or suggesting future challenges.
A positive sentiment is conveyed through the encouragement of feedback and the invitation to follow for more content, indicating the author's desire to contribute to the learning and enjoyment of others in the field.

Solution

if we open the file, we get the following string:

YidkM0JxZGtwQlRYdHFhR3g2YUhsZmF6TnFlVGwzWVROclgyMHdNakV5TnpVNGZRPT0nCg==

this looks like a base64 string, so let’s try and decode it. the result would be this:

b'd3BqdkpBTXtqaGx6aHlfazNqeTl3YTNrX20wMjEyNzU4fQ=='

However, the result still looks like a base64 encoded string. it seems like the data might have been encoded multiple times. so we decode it again. Note that I removed b’’ from the string and decoded the rest:

wpjvJAM{jhlzhy_k3jy9wa3k_m0212758}

now this format looks like our flag, so we’re close! let’s try decoding it using Caesar cipher. I used this site which generates all the possible outputs.

Caesar Cipher Decoder

flag: picoCTF{caesar_d3cr9pt3d_f0212758}

if you’re looking for more solutions, make sure to visit this repo.

Did you find this helpful? If you liked it, please give it a thumbs up and follow for more! Feel free to ask any questions or suggest CTF challenges for future posts.

Happy hacking!

interencdec picoCTF2024 | Write-up

Description

Hints

Solution