crypto

52 Articles

Breaking Disk Encryption With RAM Dumps

February 21, 2008 by 42 Comments


If you haven’t gotten a chance yet, do watch the video of this attack. It’s does a good job explaining the problem. Full drive encryption stores the key in RAM while the computer is powered on. The RAM’s stored data doesn’t immediately disappear when powered off, but fades over time. To recover the keys, they powered off the computer and booted from a USB disk that created an image of the RAM. You can read more about the attack here.

How can you reduce this threat? You can turn off USB booting and then put a password on the BIOS to prevent the specific activity shown in the video. Also, you can encrypt your rarely used data in a folder on the disk. They could still decrypt the disk, but they won’t get everything. I don’t think this problem will truly be fixed unless there is a fundamental change in hardware design to erase the RAM and even then it would probably only help computers that are powered off, not suspended.

The potential for this attack has always been talked about and I’m glad to see someone pull it off. I’m hoping to see future research into dumping RAM data using a USB/ExpressCard with DMA access.

24C3 Mifare Crypto1 RFID Completely Broken

January 1, 2008 by 22 Comments

Another highlight for us at CCC was [Karsten Nohl] and [Henryk Plötz] presenting how they reversed Philips crypto-1 “classic” Mifare RFID chips which are used in car keys, among other things. They analyzed both the silicon and the actual handshaking over RF. Looking at the silicon they found about 10K gates. Analyzing with Matlab turned up 70 unique functions. Then they started looking “crypto-like” parts: long strings of flip-flops used for registers, XORs, things near the edge that were heavily interconnected. Only 10% of the gates ended up being crypto. They now know the crypto algorithm based on this analysis and will be releasing later in the year.

The random number generator ended up being only 16-bit. It generates this number based on how long since the card has been powered up. They controlled the reader (an OpenPCD) which lets them generate the same “random” seed number over and over again. This was actually happening on accident before they discovered the flaw.

One more broken security-through-obscurity system to add to the list. For more fun, watch the video of the presentation.

ToorCon 9: Crypto Boot Camp

October 19, 2007 by 3 Comments

[Rodney Thayer] gave a 2 hour seminar on cryptographic technology. It was designed to give the audience a working knowledge for dealing with vendors. He gave some rules of thumb for choosing encryption. In order of preference, when doing symmetric key crypto: use AES with a minimum 128bit key, if not that 3-key Triple-DES, or last RC4 with 128bit key. For hashing: SHA 256 preferred, SHA 1 if you can’t do any better, and MD5 if you can’t SHA. For public key: RSA using at least a 2048bit key. The top choices in these lists were picked because they’ve stood up to years of scrutiny. One major theme of talk was to never roll your own crypto algorithm or buy someone elses. Proprietary algorithms get broken all the time, like the GSM A5 crypto we talked about earlier this year.