With differential power analysis, or DPA, a hacker monitors variations in the electrical consumption of a card that performs encryption functions--then performs reverse analyses to determine passwords. Cryptograph Research discovered this type of attack during the '90s.

To execute a DPA attack, the device must be in the hands of the attacker. So, while a thief could use this approach to determine the password of a bank card, a more common scenario would be for a hacker to use it to unblock pay TV signals on his or her home cable box. Cryptography Research recently obtained more than 60 patents for technology it has developed to defend against these attacks.

By Michael Kanellos at CNET.

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