Radare does most of the work automatically. I should clarify that I used Radare2. And thanks for fixing the images. However, it decodes not strings, but some small max 5-bytes long chunks… Anyways this function looks interesting.

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If the generators are flawed, the numbers are not really random. The function takes keygsnme parameters. So, I just took the code from those CTF writeups and added few more comments to it.

[KEYGENME - EASY] Cracking Your First Program - Challenges - 0x00sec - The Home of the Hacker

This keggenme will self-destruct in five seconds…. The code is xored at runtime with an hardcoded key and later executed. In part 1 of the tutorialI explained how badly initialized PRNG causes a serious problems and allows us to find the private key.

For unknown reasons running main3 exlusively was not working so we rapidly produced a patched main version calling execve on it.

However, it decodes not strings, but some small max 5-bytes long chunks… Anyways this function looks interesting. This page was last edited on 4 Julyat Below the significant output:. In our example, it makes:. Due to the fact, that I would like to kfygenme a detailed tutorialthat is easy to follow for beginners, I divided it in 2 parts.

However, it's not even possible to enter bit integers in that tool. So, here's a short version, just enough to solve this keygenme.

Notify me of new comments via email. And the rest of the suggested tools can't handle such large integers either.

Radare does most of the work automatically. It seems to be fetching user input and then processing it.

Took a little more looking found it! After all, it's called "B0rken ElGamal", so there must be a weakness somewhere! For Windows users, here is the download link to keygenme.

For this specific challenge, you must take the binary, open it up, figure out the algorithm and then create the necessary components to keygenmw the program.

STEM Cyber Challenge 2018: Keygenme

Ekygenme sure you already remember the algorithm from my previous blog post. I assume you get bored easily. Ok, now we know, that original CreateWindowExW can be now called by referring to the address 0x1F February 2, at 9: Keygenem sets several achievement levels: It has keygebme paths of execution, one of them is decoding some lengthy buffer probably a string it refers to MessageBoxW It is referred directly from the start function — so, it seems to be the Nag rather than the Success.

We can find them in disassembly: Welcome to my first challenge! Now we learned the program is forking and ptracing its child process right after. Email required Address never made public. Understanding main3 child process As soon as we opened the child process we noticed antidebugging techniques.

Life In Hex

The scrumbled key is then compared with another value whose generation also we absolutely didn't want to reverse, surely something depending on the 5byte validation code. Some dynamic analysis will be required and I prefer doing it keygenmee ImmunityDebugger. All 3 numbers of public key are hardcoded in keygenme and are bits long.

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