Security researchers have published a paper warning that LED status indicators on datacomms kit can leak information to eavesdroppers.
A paper, Information Leakage from Optical Emanations, by Joe Loughry of Lockheed Martin Space Systems and David A.Umphress of Auburn University in Alabama explains how it's possible to correlate flickering lights with information flowing through a device.
On the face of it this seems impractical but the researchers have carried out tests which show "that it is possible to intercept data under realistic conditions at a considerable distance". Snoopers could intercept data from at "least across the street" using inexpensive equipment (which they haven't actually built yet), they suggest.
"Many different sorts of devices, including modems and Internet Protocol routers, were found to be vulnerable" to what the researchers describe as an "Optical Tempest" attack. Tests suggest lower speed device (such as 56Kbps) might be most subject to the theoretically undetectable attack.
The ability to monitor computer by intercepting stray radio-frequency emanations computers and displays has been common knowledge for some time, but there's been little mention of spying on signals in the optical spectrum.
One drawback is that such signals may be a noisy representation of the data flowing through them, as Loughry and Umphress acknowledge. Another difficulty, is that an attacker would need line of sight for effective snooping.
Paranoid punters may want to review that paper on the subject before deciding if they need to put duct tape over their LEDs or equipment redesign, both of which are suggested as countermeasures by the researchers. ®