Decius wrote:

If an attacker wants to learn the IP address of a hidden server on the Tor network, he'll suddenly request something difficult or intensive from that server. The added load will cause it to warm up.

Because temperature affects how fast most electronics operate, warming up the machine causes microscopic changes in clock skew over time. Now the attacker queries computers on the public internet that he suspects of being the Tor server, looking for the shift in skew over the course of hours.

Heating a crystal well above ambient temperature is also used to stablize the resulting signal. Most crystal ovens operate around 170 degrees F which allows the crystal stablity to approach 1x10^8, or an error of 1 hz at 100 MHz. Most oscillators used in PCs are as cheap as they come, which can result in large variations.

Lastly, this is an interesting idea given that my MacBook Pro nominally runs about 140 degrees F, and 100 degrees F at the hard disk. And the processor goes to 170 degrees F when I actually start doing serious work.

RE: Wired News: Computer Warming a Privacy Risk