Quantum cryptography

Quantum cryptography is the use of quantum mechanical effects such as quantum communication and quantum computation to perform cryptographic tasks. Its most well-known application is quantum key distribution. This is the set of protocols used to share encryption keys between two remote parties, while guaranteeing transmission security using the laws of quantum physics and information theory.

The various quantum cryptography protocols

There are several quantum cryptographyprotocols. The protocol developed by Bennet and Brassard in 1984 is frequently presented and uses photon polarisation. It is called the BB84 protocol. The E91 protocol was devised by Artur Ekert in 1991. It uses a pair of entangled photons and therefore depends on the EPR effect demonstrated by the experiments made by Alain Aspect and his colleagues.

Applications of quantum cryptography

For many years now quantum cryptography has been more than a theory or a laboratory curiosity. It was used for the first time in 2004 in a large financial transaction requiring absolute security and in 2007 when the Swiss company id Quantique sent the results of national elections to Geneva.

Naturally, quantum cryptography is of great interest to the military. DARPA (the American Defense Advanced Research Projects Agency) has been using quantum key distribution since 2004. The European Union responded to the Echelon spy programme by introducing the Secoqcnetwork.