Talked about for decades, a quantum code key system joined to the Internet has now been demonstrated. It sends encoding and decoding keys as light pulses between Harvard and Boston universities and BBN Technologies, a hi-tech company in Cambridge, Mass. The network started operating in June 2004. “Our team has been able to develop a laboratory curiosity into a working system that is being tested and refined for use in sending secure messages,” says Harvard project scientist John Myers. The Achilles’ heal of secure communications via the Internet has been the cryptographic keys necessary for encoding and decoding messages. At present, such keys depend on long sets of numbers that would take eavesdroppers tens or hundreds of years to crack. But coders worry that advances in mathematics or the technology of quantum computers could shorten that time to seconds. “If that happens,” Myers notes, “messages we want to keep secret would be an open book.” Theories of quantum mechanics suggest that cryptographic keys can be distributed by light signals so weak they come close to being no signal at all. Any eavesdropper who reads such faint signals would disrupt them and be easily noticed. If that were to happen, communicators could quickly discard the tampered-with keys and set up an alternate route for exchanging a new key.