OJ's rants » ASM

Reversing DirectX & Blowfish

OJ — Sun, 08 Apr 2007 20:31:18 +0000

This tutorial has been on the boil for quite a while. I got close to nailing the problem late last month, but didn't end up finding the time to finish it until this weekend. This tutorial is a solution to another Crackme, but this time it's really not for the faint-hearted. Information on reversing fullscreen DirectX (Direct3D) applications and playing around with Blowfish can be found in this tutorial, and it's a bit of a mind-job - it also weighs in at nearly 40 pages (with some nice pictures thrown in)!

The crackme, by Silver, can be found here, and the solution can be found here on my site (or on Crackmes.de when approved).

I'd love to hear your thoughts

Another Lesson in Software Reversing

OJ — Thu, 08 Mar 2007 11:10:58 +0000

Yes, you can (most probably) consider this to be a fairly regular segment from this point on As I said before I've always been partial to RCE, and I don't think I'll ever get sick of it. Today's installment is another tutorial that I felt shouldn't be published. The reason is because it's a tutorial on how to solve an example reversing challenge for the IITAC online RCE adacemy, and I generally don't think it's a good move to show other people how to do this stuff when they can get certified for it. However, this is just a training example so I think I'm safe.

The challenge consists of a few tasks:

Removing a nag-screen
Finding a hard-coded serial number
Finding a valid name/serial combination
Writing a key generator

You'll notice from the tutorial that the full source code is included written in 32-bit ASM. Again, I would appreciate the feedback on the quality from anyone who wishes to give it (that includes you Alister ) as I'm always looking to improve what I write.

You can grab it from here.

A Reversing Tutorial

OJ — Fri, 02 Mar 2007 14:24:39 +0000

For a long time I've been interested in the lovely and exciting art of Reverse Code Engineering (RCE) and on more than one occasion I've been sucked in to spending hours and hours delving through pages of ASM code searching for the answer.

Today is no different. With Amy feeling pretty crook due to a nasty headache, I thought I'd retire to my PC and do something quiet that I haven't done for ages. So I downloaded a crackme from Crackmes.de and started reversing. After nailing the problem to the wall, I decided to unleash my learnings on the world via a tutorial. When coders go through the rigmarole of producing these little apps for people like me to play with, it seems only fair that I give back with a bit of information on how I broke their protection scheme. Not just that, but it gives other wannabe-reversers something to read and learn from to.

For those of you who are interested in reading and learning the basics, feel free to download the goods. Any feedback is appreciated (but only if it's good ).