With enough technical savvy, simply touching a laptop can suffice to extract the cryptographic keys used to secure data stored on it.

The trick is based on the fact that the “ground” electrical potential in many computers fluctuates according to the computation that is being performed by its processor—including the computations that take place when cryptographic software operates to decrypt data using a secret key.

Measuring the electrical potential leaked to your skin when you touch the metal chassis of such laptops, and analyzing that signal using sophisticated software, can be enough to determine the keys stored within, says Eran Tromer, a computer security expert at Tel Aviv University.

The remarkable result is described in this paper due to be presented at a conference in South Korea next month, but it was demonstrated Tuesday at a cryptography conference in Santa Barbara, California.

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