on validation. Much of the interest in quantum cryptography stems from the fact that the approach is fundamentally secure. This contrasts with today's code-based systems, which rely on the assumed difficulty of certain mathematical opera- tions. Quantum cryptography would provide a communication method utiliz- ing secrecy that doesn't depend on any assumptions. Quantum cryptography allows two users on an optical fiber network to form a shared key, the secrecy of which can be guaranteed. The technology takes advantage of the particle-like nature of light. In quantum cryptography, each transmitted bit is encoded on a single light particle (or photon). The impossibility of faithfully copying this stream of encoded photons ensures that a hacker can never determine the key without leaving detectable traces of intervention. Until now, quantum cryptography's major limitation is that light particles could be scattered out of the fiber. In theory, this isn't critical, since only a tiny fraction of the photons that reach a fiber's end point are used to form the key. In practice, however, the rate of photons surviving long fibers can be SO low that they are masked by noise in the photon detector. By developing an ultra- low noise detector, the Toshiba team has been able to demonstrate a system working over much longer fibers than achieved previously. "As far as we are aware, this is the first demonstration of quantum cryp- tography over fibers longer than 100 kilometers," says Andrew Shields, who THE UNBLINKING EYE-SECURITY AND SURVEILLANCE leads the Toshiba group developing the system. "These developments show that the technique could be deployed in a wide range of commercial situations within a time frame of less than three years." Michael Pepper, joint managing director of Toshiba Research Europe, notes that advancements in semiconductor technology are allowing his researchers to implement quantum effects that were previously known only in theory. "One can foresee that this is the beginning of a process which will lead t