Filiol demonstrated what he called the Windows Jingle Attack, a method for encoding a user's password into audio data and concealing that data into the Windows startup tone, a publicly audible sound that can be read from afar with a local or remote microphone and then decoded.
Filiol's work builds on what's known as Tempest. Filiol said the term stands for Temporary Emanation and Spurious Transmission, though others suggest alternate terms to explain the acronym.
Tempest refers to research done by the NSA into the signals that emanate from electronic devices and how to prevent the interception of those signals. The reason is that those signals may reveal the information being processed by a device or may be altered to do so.
Programmer Eric Thiele has written a demonstration program called Tempest for Eliza that uses a computer monitor to send out AM radio signals.
The Windows Jingle Attack requires malware on the target machine, so in that respect it's not as easy to execute as other attacks that allow remote code execution. Nonetheless, there are certain scenarios when being able to obtain data from a computer without a network connection would be valuable.
There's precedent for related attacks in the intelligence community. In 1987, the National Security Agency found that the Soviet Union's KGB had replaced the circuit boards and power cords in the U.S. Embassy in Moscow in order to covertly siphon message data.
"An isolated computer is quite never really disconnected from the outside," said Filiol. Through social engineering or covert insertion, malware can be introduced to an offline computer. Law enforcement agencies have used this technique to install keylogging hardware for surveillance, which they then have to retrieve to obtain captured data. Filiol's technique saves the need for this second visit.
The Windows Jingle attack requires malware with audio-processing code to encode the information to be stolen. Filiol suggests the open source Scilab program as a starting point. The malware needs to be able to replace the Windows startup tone. And the person receiving the information needs some means to pick up the startup tone -- a microphone that works over long distances or hidden locally, and software to decode the transmitted information.
Filiol said that he called the attack the Windows Jingle attack as a matter of convenience. He said that it would work just as well on a machine running Mac OS X or Linux.
Filiol's technique can be used to create other covert channels of communication. He said that data could be encoded visually on-screen, using hard disk read/write noise or computer fans.
When playing an actual altered Windows startup tone, the results were impressive. He demonstrated a startup tone where the encoded data could be heard, and then he demonstrated an optimized version where the presence of hidden data was undetectable to the human ear.
Filiol said he would post a hidden message in his presentation materials in the Black Hat archives, which should be available in about two weeks. He promised a token prize to the first person to decipher the message.