Data security problems


Consider two different security problems. In the first, you store your valuables in a safe in your basement. The threat is burglars, of course. But the safe is yours, and the house is yours, too. You control access to the safe, and probably have an alarm system.

The second security problem is similar, but you store your valuables in someone else’s safe. Even worse, it’s someone you don’t trust. He doesn’t know the combination, but he controls access to the safe. He can try to break in at his leisure. He can transport the safe anyplace he needs to. He can use whatever tools he wants. In the first case the safe needs to be secure, but it’s still just a part of your overall home security. In the second case, the safe is the only security device you have.

This second security problem might seem contrived, but it happens regularly in our information society. Data controlled by one person is stored on a device controlled by another. Researchers found a new attack against implementation of the RSA cryptosystem. The attack exploits the fact that different operations take different times on modern CPUs. By closely monitoring the CPU during an RSA operation an attacker can recover the key.

These sorts of attacks are not new. In 1995, researchers discovered they could recover cryptographic keys by comparing relative timings on chips. In later years, both power and radiation were used to break cryptosystems. These were most useful to recover secrets from smart cards.

The solution to this security problem lies in removing the separation. This means completely redesigning the system and the security assumptions behind it. But separating data ownership and device ownership doesn’t mean that security is impossible, only much more difficult. You can buy a safe so strong that you can lock valuables in it and give it to your attacker with confidence. But one cannot be so sure he can design a smart card that keeps secrets from its owner, or a DRM system that works on a general-purpose computer. But in all cases, the best way to solve the security problem is not to have it in the first place.