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Cryptography is about scrambling information so that it is unintelligible to anyone but those who know how to decode it using a secret key. Up until today, existing cryptosystems use software solutions based on mathematics to distribute keys. Mathematics are penetrable - an intruder can copy a classical key, decode it and expose data leaving no evidence of his snooping.

Quantum Cryptography is a new approach to the key distribution problem and is the absolute security technology to protect voice, data or video communications. Instead of transmitting keys, this technology generates them dynamically using quantum physical phenomena which makes unbreakable security possible for the first time.

The difference with Quantum Cryptography is the sender simply transmits a string of bits to the receiver whose values are carried by single photons. If an intruder tries to intercept them, their state will irreparably changed. The sender and receiver will detect eavesdropping and the transmitted string of information is discarded. These suspect bits will not be used to establish the key. Only undamaged photons provide risk-less information to forge a step-by-step secret key.

In digital cryptography, an intruder’s attack can be undetectable. The intruder is able to make identical copies of transmitted messages and then perform extensive computer analysis off-line. This is unnoticeable espionage and with today’s traditional cryptosystems, there is no defence against this type of interception.

In contrast, Quantum Cryptography will always detect intruders and eradicate eavesdropping. If an intruder attempts to clone the information carried by the photons riding on the optical link between legitimate users, quantum mechanics guarantees that this attack will lead to disturbance. Both users postpone sending any valuable information until the security of the optical link is assured.

For the very first time in the history of cryptography, unbreakable communications via optical links are made possible by using the laws of quantum physics.

Advantages of Quantum Cryptography

Quantum Cryptography fulfils some of the digital cryptography security functions. It therefore provides a brick of additional security to existing digital cryptography systems.

• It gives the ability to provide absolutely secured keys
• It gives the ability to detect intruders and eradicates espionage on optical networks
• It allows high-speed key updating
• It simplifies the key management and suppresses the risk due to key saving
• It provides timeless security based on the universal laws of quantum physics
• Finally, it removes the human risk within the security chain

Single-Photon devices for quantum cryptography communications

The ultimate in cryptography communications, is the development of single-photon detection devices that make possible low-noise, high-speed operation and single-photon generation devices with a low incidence of simultaneous generation of multiple photons. State of the art is a high-speed detection device with a dark count probability of 10-9 per ns or less and operating frequency of 3 Mhz or higher (Toshiba). It contains a single-photon generation device: within a resonator structure, self-organized InAs quantum dots have been selectively grown on gallium arsenic and confirmed the generation of single photons in the optical communications waveband by electrical drive.