Best-Kept Secrets -- Quantum cryptography is here!

Excerpt: What kept the key from prying eavesdroppers was Heisenberg's uncertainty principle--a foundation of quantum physics that dictates that the measurement of one property in a quantum state will perturb another. In a quantum cryptographic system, any interloper tapping into the stream of photons will alter them in a way that is detectable to the sender and the receiver. In principle, the technique provides the makings of an unbreakable cryptographic key. Science & Technology at Scientific American.com: Best-Kept Secrets -- [ INNOVATION ] -- Quantum cryptography has marched from theory to laboratory to real products