World-Changing Technologies

In your article about quantum cryptography ("10 Emerging Technologies That Will Change the World," TR February 2003), Nicolas Gisin claims that quantum technology will eliminate the possibility that increasing computer power could be used to crack existing security codes. The amount of computation required to crack a given cipher rises geometrically with the number of bits used for the keys, whereas the computer power needed to encrypt and decrypt data depends only linearly on key length. If this relationship holds, it doesn't matter how fast computers become; we need only to increase key length. Nevertheless, some particularly clever person could invalidate these assumptions about cracking ciphers. Perhaps that's the risk Gisin strives to protect us from.

Jim Roberts
Wilmington, DE