With the growing popularity of CTF (capture the flag) competitions, and the excellent performance of Polish teams like Dragon Sector in this area, I thought it would be interesting to demonstrate the construction of a simple CrackMe, using some creative techniques which make it difficult to crack and analyse.

If you have ever been curious about reverse engineering, entered a CTF competition, or wanted to create your own CrackMe and drive other contestants crazy, this is for you.

You can find an article about the crackme with detailed technical description and source code commentary (in english) at:

https://www.pelock.com/articles/how-to-write-a-crackme-for-a-ctf-competition

https://zaufanatrzeciastrona.pl/post/jak-napisac-ciekawe-crackme-na-ctf-instrukcja-krok-po-kroku/

If you already have some reversing skills, and would like to try your hand at the CrackMe I am about to describe in detail, put this article aside, get the compiled executable, and try to find the flag!

Once you've made your best attempt at it, you can come back to the article and compare what you discovered against the full story. This CrackMe has a medium level of difficulty.

https://www.pelock.com/download/CrackMeZ3S.zip

To run the CrackMe executable you may need the Visual C++ Redistributable Packages for Visual Studio 2013.

Got the CrackMe? Don't cheat by reading any further - get cracking! ;)

Otherwise, if you want to learn how to build your own CrackMe, I invite you to keep reading...

Bartosz Wójcik https://www.pelock.com