Quantum Key Distribution Verification System

Quantum information technology has attracted a lot of attention in recent years because of the promise it holds for more secure future communications. Simultaneously the quantum algorithms are even capable of factorizing numbers more efficiently than any known classic method is, thus challenging the security of public-key cryptosystem such as the RSA system. The most advanced field in quantum information technology is quantum cryptography, also referred to as quantum key distribution (QKD), which uses the quantum properties of light to ensure the unconditionally secure transmission of a secret message between two remote parties. Especially we can realize ultimately secure communication based on the well-established one-time pad cryptosystem using QKD.The DPS (differential-phase-shift) QKD protocol was invented by NTT and Stanford University working in collaboration in 2002, led by K. Inoue and Y. Yamamoto, and the QKD system based on DPS protocol has a simple configuration which is easy to implement with conventional optical communication components, and it is suitable for a high-clock rate and long-distance QKD system. Moreover, although the DPS-QKD system is implemented with an attenuated laser source, it is inherently secure against strong eavesdropping attacks called photon number splitting attacks, which pose a serious threat to conventional QKD systems with attenuated laser sources.This paper describes QKD related technologies, including preparation of single photon source and single photon detector technologies, and introduces a typical and widely used QKD protocol BB84 and then overviews a recently proposed scheme called the differential phase shift protocol. Then we analyze the security of the DPS protocol and showed that it is robust against strong non-coherent attacks by Eve, including a photon number splitting attacks and individual attacks. The security proof is derived by bounding the average collision probability, which leads directly to a bound on Eve's mutual information on the final key. At last we presented our QKD demonstration experiment, in which we implemented the differential phase shift QKD protocol. We employ the secret keys distributed to encrypt a piece of multimedia information by AES (Advanced Encryption Standard), while we decrypt the encrypted information using the same secret keys in real time. The progress of implementing the QKD system included the related hardware design and software programming. The hardware module realizes the function of signal acquisition and transmission, which is from the single photon detector. The software module realizes the function of the encrypted information transmission on the classical channel, while finishing the secret key comparison between the two parties.