msramdmp: McGrew Security RAM Dumper
Creating bootable USB drives for capturing the contents of memory
Hello CanSecWest 2008 Attendees! Check out this blog post for links to more information on this site on the topic of msramdmp.
Overview
A short while back, a paper was published by researchers at Princeton University, in which they talk about the process of recovering encryption keys out of memory after a cold boot. This was surprising to many people, as most just assume that, since RAM is volatile storage, it is erased when power is removed. This is an incorrect assumption.
When the idea of memory retaining state for a short time was first brought to my attention a little over a year ago, I ran a few experiments similar to this one, just to prove it to myself. The desktop machines I tried would hold state for anywhere between 5 and 10 seconds without power, whereas my laptop, with no battery or wall power, would maintain state for an amazing 10 minutes. I used a Linux bootable CD to get an image of memory from a Windows to data carve, and found some interesting things. The footprint for the Linux OS was huge, though, and this interfered with my ability to capture as much memory from the previously running operating system as possible.
The Princeton researchers applied this method to the recovery of encryption keys, with great results. They also cooked up a way to image the contents of RAM with a very small footprint, only overwriting a small amount of memory in the process. Unfortunately, at the time of writing this, their tool, ram2usb, hasn't been released. I decided that it wouldn't be hard to go ahead and implement one myself, based off their paper and youtube video posted above, so that I (and others) can go ahead and start having fun.
So, as a small side project, I've written "msramdmp", the McGrew Security RAM Dumper. Enjoy!
Download
msramdmp.tar.gz - The compiled com32 executable, ready for use with SysLinux. Also, the C source code is included, along with some things needed to compile and link it properly.
This version fixes a bug where the first section of memory wasn't being dumped correctly. Redownload if you downloaded this before 2:00PM March 5th, 2008.
- syslinux-3.61.tar.gz - This is the exact version of SysLinux that I'm using here. You'll need this to prepare a USB drive for capturing RAM, and to compile modifications to the msramdmp source.
- msramdmp_cd.iso - This is a bootable CD version of msramdmp that I made with isolinux. Please read this blog posting for information on using this. You'll still need a drive hooked up that msramdmp can write to through BIOS interrupts.
Usage
This isn't the most user-friendly program out there. It's small, low-level, and your only real recourse, if it doesn't do exactly what you want it to do, is to hack at the code yourself. Or email me if you're in a real bind ;) . It's also very hard to test this for proper operation in a lot of different situations since I just don't have the hardware. If something does go wrong and you manage to figure out why, definitely let me know the situation.
msramdump is compiled into a standalone "com32" application that SysLinux executes. So, it's tiny. To get this up and going on a USB drive, you're going to have to prepare it properly. I'll give a demo on how to do this in Linux, but the concepts should apply to wherever you want to do it.
For this demo, I'll be showing screenshots from preparing a 1 gig flash drive in my Linux V