10 Dec 2020
We need to recover the flag from a file that has been encrypted using a random 40000 byte long key using a custom encryption routine, using only the 1 known ciphertext. Overall I found this challenge to be quite interesting and well designed. Only 3 teams solved it over the course of the 48 hour contest (organized by Perfect Blue), and it had a final score of 443 points. This post describes how I solved...
25 Sep 2019
In this challenge, we need to recover a message that is encrypted through 4 different RSA keys, while knowing some of the bits of the private keys. In particular, we are given code that generates 4 different RSA keys (of ~2100 bits each), permutes them, encrypts the flag by each of them in succession, and then provides us the encrypted flag. Additionally, we are given the moduli of the keys, as well as the lower...
24 Oct 2018
Last weekend was HITCON CTF 2018, and it was really awesome! I
personally spent time on various super interesting challenges. Below
is just one of them that I happened to solve on the first day. I found
to be particularly interesting to solve since I never have had a
chance to dive into any homomorphic encryption systems before.
12 Aug 2017
Reverse engineering is a mix of an art as well as a science. Over
time, one tends to gather a repertoire of common "tips and tricks"
that one might use when reversing any given piece of software. What
follows are a condensed form of some tricks gained from Gynvael's