A laser capable of spying on keyboards by listening to them

August 9, at 32^my At the DefCon conference in Las Vegas, specialized in hacking of all kinds, Samy Kamkar showed how he managed to spy on oral or written conversations, remotely and without being seen. This businessman who is an expert in computer security, known for having hacked the social network Myspace in 2005, improved a “laser microphone” presented fifteen years ago at this same conference. One of his main tricks is to have modulated the laser, turning it off and on 400,000 times per second, to avoid interference that could damage the fragile signal it is trying to capture. It records sounds of up to 5,000 hertz, enough to recognize voices or written words, because each key on the keyboard emits a different sound. In the demonstration video, more than 90% of the letters are successfully identified.

The transcription is not done live but only takes a few minutes. “The modulation technique is well known in radio, but I think it is a bit new for lighting”explains to World Samy Kamkar, who works at the company he created, Openpath Security, and also defines himself as a researcher. In addition to advances in laser technology – it uses infrared, invisible to the naked eye, but red or green colors are also possible – and sensors, it has used various software programs developed by others, such as GNU Radio for signal analysis, or Keytap, from Georgi Gerganov, who is responsible for deciphering sounds into letters.

In 2009, a team from the University of California at Berkeley had already demonstrated, but using a real microphone, that it is possible to infer the letters that are written.

In September, on his GitHub site, amid programs to hack a drone, create fake magnetic access cards or install wipe-resistant cookies on websites, Samy Kamkar posted online the instructions that allowed him to create his system.

The technique may be more discreet than a microphone, but it is very sensitive to the quality of light transmission. To counteract this, the hacker himself suggests “Make the back of screens less reflective or not clean the windows”.