Closing security hole in popular encryption software

Side channel attacks extract sensitive information from signals created by electronic activity within computing devices during normal operation. The signals include electromagnetic emanations created by current flows within the devices computational and power-delivery circuitry, variation in power consumption, and also sound, temperature and chassis potential variation. These emanations are very different from communications signals the devices are designed to produce.

In their demonstration, Prvulovic and collaborator Alenka Zajic listened in on two different Android phones using probes located near, but not touching the devices. In a real attack, signals could be received from phones or other mobile devices by antennas located beneath tables or hidden in nearby furniture. 

The “One & Done” attack analyzed signals in a relatively narrow (40 MHz wide) band around the phones’ processor clock frequencies, which are close to 1 GHz (1,000 MHz). The researchers took advantage of a uniformity in programming that had been designed to overcome earlier vulnerabilities involving variations in how the programs operate. 

“Any variation is essentially leaking information about what the program is doing, but the constancy allowed us to pinpoint where we needed to look,” said Prvulovic. “Once we got the attack to work, we were able to suggest a fix for it fairly quickly. Programmers need to understand that portions of the code that are working on secret bits need to be written in a very particular way to avoid having them leak.”

The researchers are now looking at other software that may have similar vulnerabilities, and expect to develop a program that would allow automated analysis of security vulnerabilities.

“Our goal is to automate this process so it can be used on any code,” said Zajic, an associate professor in Georgia Tech’s School of Electrical and Computer Engineering. “We’d like to be able to identify portions of code that could be leaky and require a fix. Right now, finding these portions requires considerable expertise and manual examination.”

Side channel attacks are still relatively rare, but Prvulovic says the success of “One & Done” demonstrates an unexpected vulnerability. The availability of low-cost signal processing devices small enough to use in coffee shops or airports could make the attacks more practical.

“We now have relatively cheap and compact devices – smaller than a USB drive – that are capable of analyzing these signals,” said Prvulovic. “Ten years ago, the analysis of this signal would have taken days. Now it takes just seconds, and can be done anywhere – not just in a lab setting.”

Producers of mobile devices are becoming more aware of the need to protect electromagnetic signals of phones, tablets and laptops from interception by shielding their side channel emissions. Improving the software running on the devices is also important, but Prvulovic suggests that users of mobile devices must also play a security role.

“This is something that needs to be addressed at all levels,” he said. “A combination of factors – better hardware, better software and cautious computer hygiene – make you safer. You should not be paranoid about using your devices in public locations, but you should be cautious about accessing banking systems or plugging your device into unprotected USB chargers.”

— Read more in Monjur M. Alam, et. al., “One&Done: A Single-Decryption EM-Based Attack on OpenSSL’s Constant-Time Blinded RSA,” proceedings of the 27th USENIX Security Symposium, Baltimore, Maryland, 17-17 August 2018