Just when you thought it was safe to eat at the neighborhood deli, a group of Israeli researchers has announced they've figured out how to pull the encryption keys stored on some computers by using items which can be hidden inside pita bread.
A new device, concealed in a pita bread, is found to have the capacity to collect electromagnetic signals from a target distance of merely 50 centimeters, about 19 inches. Aptly called PITA (Portable Instrument for Trace Acquisition), the new device is made up of a copper unshielded loop antenna, an SDR receiver, controller, microSD card, Wi-Fi antenna, antenna tuning capacitor, batteries and a pita bread.
The capacitor is designed to gather frequencies within the 1.7-MHz range. These signals are then stored in the internal microSD card, which can be used for offline analysis of the keys.
"The secret key can be deduced from these fluctuations, through signal processing and cryptanalysis," the researchers wrote.
The group added it has successfully extracted keys from various models of laptops that are running GnuPG in just a few seconds. Common laptops and encryptions that have the popular implementations of EIGamal and RSA are said to be vulnerable to this type of attack. Other vulnerabilities are seen from those that implement modern exponentiation algorithms in their decryption. These include the sliding-window and the fixed-window exponentiation.
There are at least three experimental setups to mount the attack, as demoed by the researchers.
The first one, dubbed as a "Software Defined Radio" (SDR) attack, uses a simple antenna of 15 cm in diameter. The signals are recorded in an SDR receiver. The end result is an extraction of the RSA and EIGamal keys, which is achieved in a matter of seconds.
The second setup is what the researchers dubbed as "Untethered SDR" attack. There are two operation modes to choose from iun this type of setup: online mode and autonomous mode. Both cases perform offline signal analysis on a workstation.
The third setup, "Consumer radio" attack, uses a plain consumer-grade radio receiver instead of an SDR receiver and a magnetic probe. This setup records the signal by establishing a connection with the microphone input of a 4G smartphone.
For the third setup, the researchers have decided to build a second device which they called the "Road Master."
"We then recorded the signal by connecting it to the microphone input of an HTC EVO 4G smartphone," wrote the researchers.
The research paper was co-authored by Eran Tromer, Itamar Pipman and Lev Pachmanov, who are all from the Tel Aviv University. Daniel Genkin, who is from both the Tel Aviv University and Technion, is also one of the authors. The paper will be presented at the Workshop on Cryptographic Hardware and Embedded Systems 2015 in France in September.
To fix the problem and avoid what they term a "side-channel attack," the researchers recommend either working in a Faraday cage (check, easy to bring to the deli every noontime) to mitigate electromagnetic radiation leaks, or changing the cryptographic software.
"Inexpensive protection of consumer-grade PCs appears difficult. Alternatively, the cryptographic software can be changed, and algorithmic techniques employed to render the emanations less useful to the attacker," they wrote in a Q&A about their technical paper on a Tel Aviv University website. "These techniques ensure that the rough-scale behavior of the algorithm is independent of the inputs it receives; they usually carry some performance penalty, but are often used in any case to thwart other side-channel attacks. This is what we helped implement in GnuPG."
