Sunday, 2 February 2020

(Finally) Solving the Weasel keygenme


Back in 2016, kao posted the weasel keygenme on Tuts4you. It consisted of two parts - a custom VM in C# and some crypto. The VM implemented the main logic of the keygenme. In my previous writeup about the challenge, I succeeded in partially solving the challenge by devirtualizing the VM. The crypto part was left unsolved. This was mainly because the crypto logic was way too complex and without special algorithms there was no way to have a go at it. As described in my earlier post, even SAT solvers have no luck in cracking the crypto.

However this time after nearly 4 years I am happy to say that I did manage to break the crypto. In this blog post I will describe the process to solve this keygenme along with all the failed attempts.

Initially I planned to post the write-up on this blog but the blogger platform is not too good for handling equations and mathematical terms. Hence I have left the write-up as an IPython notebook on Google Colab which has been embedded as a GitHub Gist below. In case the preview below doesn't load properly on your browser you can always find the original notebook on Colab.

https://colab.research.google.com/gist/extremecoders-re/cc268753b6d25017fe0cff7299ad9be3/-finally-solving-the-weasel-keygenme.ipynb

The keygen can be found on GitHub

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