Black Bauhinia coorganized HKCERT CTF 2021 and helped 95% of the technical stuffs, including challenge setting, platform development, infrastructure and etc. I will be writing a series of blog posts talking about the contest, and the first four would be the writeups of the challenges those I wrote.
In the first blog post, we will be going through four easier crypto challenges: A Joke Cipher, Cipher Mode Picker, Key Backup Service 1 and Key Backup Service 2.
No, we did not win. I see that coming and took a screenshot during the game.
BSides Ahmedabad CTF 2021 is organized by @zer0pts. That implies that players could spend a day happily working on the challenges. I enjoyed working on the challenges a lot. I’ll go through the harder crypto challenges and the reversing challenge called Collapsed License in this blog post.
LagLeg is a crypto challenge in ASIS CTF Quals 2021. We are asked to factor a given $n$ with $n = (r^5 + s)(r + s)$ as part of the challenge. Hereby $r$ and $s$ are respectively 256 and 64 bits long. I think my approach used is very unique and creative - and definitely worth mentioning. It does not mean that it is a good approach, however.
I will record the exact steps I solved the challenge. However, I will update the bounds and prove the whole thing so that it looked more rigorous. The full code will be attached at the end of the blog post, too.
I am playing as a part of @blackb6a this time for perfect blue’s annual pbctf. This time there are six crypto challenges and I first blooded 🩸 half of them. I solved five of them, and collaborated with TWY (who made 99% of the process) for Seed Me. In this blog post, I will cover Seed Me and Yet Another RSA. I tried to make the whole post beginner friendly, hence included more details than necessary.
I was originally going to discuss all of the crypto challenges, but I found it is too demanding and tiring.
