science

Quantum cryptography has the potential to guarantee perfectly secure communications, but until now all of the prototype systems have been point-to-point links rather than networks that share connections.

BBN Technologies, Harvard University, and Boston University researchers have built a six-node quantum cryptography network that operates continuously to provide a way to exchange secure keys between BBN and Harvard, which is about 10 kilometers away. The researchers will soon move one of the network nodes across town to link Boston University into the network.

Quantum cryptography schemes allow a pair of correspondents to securely exchange a one-time pad, or key that will unlock a scrambled message. The schemes call for transferring each bit of information using a single photon. The systems are potentially very secure because the quantum state of a particle cannot be observed without altering it.

The Defense Advanced Research Projects Agency (DARPA) Quantum Network will allow BBN and Harvard to each exchange secure keys with Boston University via a single, shared fiber.

The quantum network uses secure point-to-point connections between nodes and allows a given node to relay secure cryptographic keys between two other nodes. The network contains a optical switch that can change the way the nodes are connected.

Multiple connections to and from any given node means the network will stay up even if one node goes down.

The network is ready for practical applications today.

Technology Research News: http://www.technologyreview.com/articles/04/07/rnb_071904.asp?trk=nl