Project maintained by dm248 Hosted on GitHub Pages — Theme by mattgraham

[Tarock] [Rubik]


Double XOR

May 28, 2021

If you were wondering about how to solve the Double XOR challenge at b01lers CTF 2021, then your wait is over. The solver was ready ages ago (to field the problem I obviously had to break it first) but it took a looong while to finally type it up …

Some thoughts on b01lers CTF 2021

Apr 14, 2021

b01lers CTF 2021 happened about 10 days ago. I hope that each participant had a good time :) With the experience from last year, it went pretty much flawlessly IMO…

Curious case of (13,4,1) shellsort

Oct 15, 2020

I tend to think back fondly to the good old times when I was a student but I must have had it easy. Here is an assignment someone else got recently: Find the worst-case input for (13,4,1) shellsort on 25 elements. The official solver offered was simple, just shy of 1 billion core years to run - trying all 25! permutations. So that got me curious, is the problem doable? Well, it turns out that it is, just not quite that way…

b01lers bootcamp CTF

Oct 8, 2020

We hosted bootcamp CTF last weekend, This time I went for easy difficulty and made a whole bunch of minichallenges (aka Crypto World). Things ran very smoothly, only a few minor lessons to learn from…


Jul 26, 2020

I tried a couple problems at UIUCTF last weekend, crypto and pwn mostly. It had an interesting mixture of simple and hard problems with not much in between. Overall, it was fun and educational…


Jun 15, 2020

NahamCon CTF was a fun event last weekend. I only had about 10 hours for it, so I did what tends to suit me best: crypto plus some misc challenges. Overall I scored close to 1500, which is OK but there is always room to do more. Here are some of my thoughts about the problems..

Where’s the Sat @ Hack-A-Sat

Jun 7, 2020

Two weeks ago, the USAF and DDS put up a Hack-A-Sat space hacking challenge. I only had time to check out a handful of the problems, one of which was Where’s the Sat that asked people to identify a satellite by location and time and then predict where it would be at another time. It turns out that with the right tools, such as Skyfield, the problem is straightforward (check, e.g., here). But the solution is not very satisfying unless one understands what goes on inside the black box… so if you are curious, read on

GitHub Pages

Jun 6, 2020

I decided to give GitHub Pages a try so that I do not have to bother with hosting these posts elsewhere. Take-off was quite smooth but not without a few hiccups…