Summary This is a detailed writeup for the “IFUCKUP” challenge at the DEF CON CTF 2023 Qualifiers that I solved together with several team members from Norsecode (a collaboration of several CTF teams, including Kalmarunionen). The challenge binary that had to be exploited permits a buffer overflow on the …

Summary This is a writeup for the “Unlimited Braid Works” challenge by mitsu at zer0pts CTF 2023. This challenge involved non-commutative group theory, and in particular braid groups. We were the first team to solve this challenge, which 6 teams solved in total. Solved by: shalaamum Writeup by: shalaamum …

Summary This is a writeup for the “anti Kerckhoffs” challenge at the Codegate 2023 Preliminaries. This challenge was built around basic abstract algebra, exploiting e.g. that evaluation of quadratic polynomials is not bijective and information about them can be recovered by comparing the cardinality of …

Summary This is a writeup for the “babyPQ” challenge by mr96 at m0leCon Teaser 2023. We were the first team to solve this challenge, with a total of 7 solves. This challenge involved lots of probabilities; there was a Feistel cipher involving S-boxes whose output bits satisfy a linear relation with high …

Summary This is a writeup for the “Collisions” challenge by mr96 at m0leCon Teaser 2023. We were the first team to solve this challenge, which had a total of 4 solves. In this challenge we had to find a second preimage for a custom hash function. Solution by: shalaamum Writeup by: shalaamum Writeup first …

Summary This challenge used garbled circuits. They have a cryptographic application, which is however irrelevant for understanding this challenge and solution. Essentially we get the bits of the flag xored by random key we do not know, but we can also define some logical gates that take the flag bits as inputs, and get …

Writeup by: ChrRaz Kuuuurveen We are given the following challenge description. A client and a server have been communicating the flag over an encrypted channel. Der er en Kuuuuuuuuuuuuuuurveeeeeee, er den ikke smuk? En client og en server kommunikere over en krypteret kommunikationskanal. Se om du ved hjælp af source …

Writeup by: ChrRaz 80s Commitments When opening http://80s-commitments.hkn we are greeted with the following page: We are given a public key and a “commitment”. If we enter this commitment into the “reveal” box we get redirected to the following page which shows an embedded youtube video. …