taviso

crackmes are small reverse engineering puzzles designed to test your binary analysis skills and showcase interesting protection schemes, similar to those used in commercial software to validate registered users. Solving them can be tough, but must be the most fun you can have with a debugger.

The goal is usually to study how the crackme works and then write a keygen or disable the protection by patching the code (if permitted by the rules), and then publish a solution explaining how you solved it to anyone else interested in learning about it.

Some knowledge of assembly is all that's required to get started, but all sorts of skills are needed to solve the tougher crackmes, from cryptanalysis, algorithm analysis, reconstructing high-level code, executable unpacking, identifying and eliminating anti-debugger and anti-disassembler tricks, and so on.

The best site for finding linux crackmes is crackmes.de, where there's a whole community of users interested in reverse engineering, unfortunately the number of linux crackmes is tiny in comparison to the number of windows crackmes, however, there are still plenty of interesting ones available. The crackmes range from the ridiculously simple to some really tough projects that can take weeks to solve.

An example of the best of linux crackmes is one of my favourite authors, crp-, who has released three very different crackmes on crackmes.de. I've just published my solution to his third crackme, and really enjoyed it.

crp-'s crackmes are here, here and here.

If you're looking for an interesting project and would like to hone your debugging, reverse engineering or hostile binary analysis skills I would highly reccommend trying out a few crackmes.