The average computer leaks information in remarkably unusual ways. In the past, we have seen Ben-Gurion University experiments demonstrating leaks through fans, headphones, heat, and even a mobile phone's radio. However, the recent work of researcher Alfredo Ortega, presented at the last Ekoparty conference, shows that a computer can share some details of its environment by turning the hard drive into a rudimentary microphone.
Many components in a computer were designed without considering the security factor. For example, I personally doubt that the developer of the first wireless keyboard thought about the possibility of intercepting entered data, but today it is a reality that only requires the exact piece of code and 15 or 20 dollars in hardware. The playing field has changed, and out there we find very high-level experts who can make computers and accessories "speak". Now, what if we make them listen? The SPEAKE(a)R technique from Ben-Gurion University transforms speakers and headphones into microphones, but what we have here is even more subtle:
A Hard Drive as a Microphone
Researcher Alfredo Ortega presented at Ekoparty 2017 a method to convert a hard drive into a microphone. According to the description, operating systems enable very high-precision timers without requesting elevated privileges. This allows measuring the response time of the hard drive's head during a read operation. That time changes with vibration, therefore it is possible to reconstruct, to some extent, the sounds that a hard drive receives. In the first video we see a hard drive recording music coming from a nearby speaker, but there is more:
Resonance Attack
With the correct resonance frequency you can knock out the hard drive. The second video reproduces a 130 Hz tone that leaves the unit unresponsive, and the Linux kernel completely disconnects it after 120 seconds. This reminds me of a certain video in which a man basically yells at hard drives in a server to induce latency. I imagine Ortega's technique has a good margin for optimization. We will soon find out.
