Physical Side-Channel Key-Extraction Attacks On PCs

A team of computer security experts at Tel Aviv University (Israel) has come up with a new potentially much simpler method that lets you steal data from computers — Just Touch it — literally.

WAYS TO ATTACK ENCRYPTION

There are different ways of attacking encryption systems. On one side, there are security vulnerabilities and weakness in the encryption algorithms themselves that make it possible to figure out the cryptographic keys.

On the other side, there are flaws and weaknesses in the people themselves that make it easier than it should be to force them to offer up the keys to decrypt something. But, Flaws and weaknesses in neither of which is necessarily quick or easy to find out, as there are several dependencies.

TOUCH AND VICTIMIZE ANY COMPUTER

According to Eran Tromer, Daniel Genkin, and Itamar Pipman, computer security experts at Tel Aviv University, using a simple electrical trick is enough for sophisticated hackers to gain access to thousands of encrypted keys through solely touching the chassis of the computer.

 

Access to encrypted keys could be used to make hundreds of digital signatures used all the time by people when creating passwords, signing contracts, or perhaps most importantly, using credit and debit cards online.

In order to victimize any computer, all you need to do is wear a special digitizer wristband and touch the exposed part of the system. The wristband will measure all the tiny changes in the ground electrical potential that can reveal even stronger encryption keys, such as a 4,096-bit RSA key.

In fact, in some cases, you don't even have to touch the system directly with your bare hands. You can intercept encryption keys from attached network and video cables as well. Researchers called it a side-channel attack.

"Our attacks use novel side channels and are based on the observation that the 'ground' electric potential in many computers fluctuates in a computation-dependent way," the researchers wrote their finding on a paper [PDF]. "An attacker can measure this signal by touching exposed metal on the computer's chassis with a plain wire, or even with a bare hand. The signal can also be measured at the remote end of Ethernet, VGA or USB cables."

The researchers also note that this attack works better in hot weather, due to the lower resistance of sweaty fingers. The team will present their research in a talk titled Get Your Hands Off My Laptop: Physical Side-Channel Key-Extraction Attacks On PCs, at Workshop on Cryptographic Hardware and Embedded Systems 2014 (CHES 2014) in Korea, on September 23th.

The actual attack can be performed quickly. According to the research, "despite the GHz-scale clock rate of the laptops and numerous noise sources, the full attacks require a few seconds of measurements using medium frequency signals (around 2 MHz), or one hour using low frequency signals (up to 40 kHz)."

The team could retrieve keys from multiple test machines running a popular open source encryption software called GnuPG, which implements the OpenPGP standard. The end results are mind-blowing, as the researchers write:

Using GnuPG as our study case, we can, on some machines:

• distinguish between the spectral signatures of different RSA secret keys (signing or decryption), and
• fully extract decryption keys, by measuring the laptop's chassis potential during decryption of a chosen ciphertext.

Although, the information retrieval was better when used with high-end lab equipment. The researchers also have successfully executed this attack by using a smartphone connected to Ethernet shielding via its headphone port, which they found sufficient in some scenarios.

The good news is that there is nothing to worry about overly grabby strangers stealing your data just yet, because the technique primarily focuses on GnuPG's encryption software, which already got a patch ready to fix the problem to limit the effects. Attackers also have to monitor the electricity changes during the decryption process, so they get hold of your data, which isn't quite easy.