NEC, the Telecommunications Advancement Organization of Japan (TAO) and Japan Science and Technology have tested a quantum cryptography system with a distance between transmitter and receiver of more than 100km.
Scientists assert that the laws of physics relating to quantum states of matter make communications using quantum effects perfectly secure and able to detect if an attempt is made to eavesdrop. The problem is that maintaining the integrity of the quantum communication is technically very difficult, including the need to detect individual photons of light accurately.
The partners achieved the milestone of transmitting and detecting a single light photon over the distance through normal low-cost optical fibre. This will allow users to engage in secure communications using existing infrastructure. Using high-quality optical fibre, the transmission distance could be pushed to more than 200km, the partners said.
These distances are long enough for quantum cryptography to be used for intercity networks in many countries.
In November, Mitsubishi Electric announced it had achieved quantum-based key exchange over a distance of 87km, a record at that time. But while Mitsubishi said it planned to commercialise its quantum cryptography technology, suppliers have yet to set a launch date for such products.
To build a fully secure integrated communication system, quantum transmission is only used for exchanging the encryption keys, which are typically 128 bits long.
The transaction can be made unbreakable because of the nature of quantum phenomena. Once the sender and receiver have exchanged encryption keys in this way, the full message is sent using standard high-speed communication methods, with the messages encrypted by the exchanged keys.
David Legard writes fot IDG News Service
This was first published in July 2003