The attack, known as differential power analysis (DPA), can be used to target an unsuspecting victim either by using special equipment that measures electromagnetic signals emitted by chips inside the device or by attaching a sensor to the device's power supply, Benjamin Jun, vice president of technology at Cryptography Research, said on Tuesday. Cryptography Research licenses technology that helps companies prevent fraud, piracy, and counterfeiting.
An oscilloscope can then be used to capture the electrical signals or radio frequency emissions and the data can be analyzed so that the spikes and bumps correlate to specific activity around the cryptography, he said.
"While the chip performs cryptography it is massaging the secret key around in various ways. This processing causes information about the key to leak through the power consumption itself," said Jun.
For instance, someone with the proper equipment could steal the cryptographic key from a device three feet away in a cafe in as short a time as a few minutes, he said. An attacker could replicate the key with the information and use it to read a victim's e-mail or pretend to be the user in sensitive online transactions.
Smartphones and PDAs have been found to leak data unless they have countermeasures in place to protect against it, which Cryptography Research offers, according to Jun.
He would not say exactly which devices could be snooped on in this manner and said he did not know of any attacks in the wild using this method.
"I think we're about to start seeing it on smartphones," he said. "These attacks are not theoretical."
This type of attack first surfaced about 10 years ago on cash register terminals and postage meters. Similar data leakage was found with smartIDs, secure USB tokens, smart cards, and cable boxes, he said.
Countermeasures can involve randomizing to throw noise into the measurements or changing the way the computation is done, Jun said.
Asked to comment on how threatening this type of attack could be, cryptography expert Bruce Schneier said the basic question is who stands to lose?
"Honestly, I don't care if someone hacks a cable box--it's not my money. Similarly, I don't care how often a bank gets robbed as long as the bank doesn't deduct the losses out of my personal account," he said in an e-mail. "But if someone hacks my phone and either steals service that I am charged for, or causes me enough hassle to change my phone number, that's bad."