BBN Technologies announced on June 3 that it has built the world’s first quantum cryptography network. The network is now operational in Cambridge MA, has 6 nodes and a number of optical switches and cryptographic key relays.
Called the DARPA Quantum Network, it generates photonic qubits for transmission through either fiber optic cable or the atmosphere, to distribute cryptographic keys that are used to encrypt and decrypt messages.
This method of securing information relys on quantum entanglement. Because quantum particles are changed by the act of observation or measurement, no tapping of the qubits is possible without being detectable. These secure keys can be used with a one-time pad cipher, which makes the entire communication absolutely secure.
Pairs of entangled photons can be created by aiming a laser through a special crystal which splits single photons into two entangled ones. One photon from each entangled pair is then sent along the comm link. When received, the photon’s polarisation is recorded, thus providing both ends of the link with the same encryption key data.
For further information, see here, or here.
Next stop, quantum computing.
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