Archive for the ‘Cryptography’ Category
Back in 2007 I wrote about how I distrusted Facebook. Now there is a new startup building a social sharing service with strong privacy guarantees. Their name is Wickr and their app is available now at the app store.
Two things would make me feel more comfortable about them thou. First, What’s their business model? We know Facebook’s business model and even if you think it’s evil, it’s a known evil. Their website claims they will offer add-on services later on. But if enough people start using it, the demands on the servers will still cost money.
Second, what is their “patent-pending Digital Security Bubble” algorithm. They clam it uses AES-256 and RSA-4096. But how does it work exactly? I’m a bit surprised they used RSA-4096, the only secure way to generate the keys is on the iPhone itself, but generating a good RSA-4096 key is sloooow… although it only needs to be done once.
The one bit of criticism I have is this: “RED UI??? Really?”.
At any rate, I really hope they succeed and get a good UI guy.
We show that disk encryption, the standard approach to protecting sensitive data on laptops, can be defeated by relatively simple methods. We demonstrate our methods by using them to defeat three popular disk encryption products: BitLocker, which comes with Windows Vista; FileVault, which comes with MacOS X; and dm-crypt, which is used with Linux.
The root of the problem lies in an unexpected property of today’s DRAM memories. DRAMs are the main memory chips used to store data while the system is running. Virtually everybody, including experts, will tell you that DRAM contents are lost when you turn off the power. But this isn’t so. Our research shows that data in DRAM actually fades out gradually over a period of seconds to minutes, enabling an attacker to read the full contents of memory by cutting power and then rebooting into a malicious operating system.
Interestingly, if you cool the DRAM chips, for example by spraying inverted cans of “canned air” dusting spray on them, the chips will retain their contents for much longer. At these temperatures (around -50 °C) you can remove the chips from the computer and let them sit on the table for ten minutes or more, without appreciable loss of data. Cool the chips in liquid nitrogen (-196 °C) and they hold their state for hours at least, without any power. Just put the chips back into a machine and you can read out their contents.
This is deadly for disk encryption products because they rely on keeping master decryption keys in DRAM. This was thought to be safe because the operating system would keep any malicious programs from accessing the keys in memory, and there was no way to get rid of the operating system without cutting power to the machine, which “everybody knew” would cause the keys to be erased.
Our results show that an attacker can cut power to the computer, then power it back up and boot a malicious operating system (from, say, a thumb drive) that copies the contents of memory. Having done that, the attacker can search through the captured memory contents, find any crypto keys that might be there, and use them to start decrypting hard disk contents. We show very effective methods for finding and extracting keys from memory, even if the contents of memory have faded somewhat (i.e., even if some bits of memory were flipped during the power-off interval). If the attacker is worried that memory will fade too quickly, he can chill the DRAM chips before cutting power.
There seems to be no easy fix for these problems. Fundamentally, disk encryption programs now have nowhere safe to store their keys. Today’s Trusted Computing hardware does not seem to help; for example, we can defeat BitLocker despite its use of a Trusted Platform Module.
Notice that this attack is particularly dangerous because it can be trivially automated. All you need is a USB drive or CD with the malicious operating system already set up. If you have access to a system (e.g. a laptop), all you need to do is shut it down and boot it up from your malicious OS and you have a copy of the DRAM and thus the encryption keys.
A little known fact from Apple hardware is that it supports setting a password in the Open Firmware which will prevent the machine from booting from any device other than the built-in hard drive. I highly recommend using this option. I believe it could help in defeating even this new sophisticated attack.
Unless the attacker is careful to freeze the DRAM and pull it out of the laptop and transfer it to another machine to read it from there, the contents will be erased while he figures out that the machine can’t boot from a different drive. It’s a simple countermeasure that is available today. It won’t work in all cases, but it certainly will defeat a fair number of them.