ua nt - p h / 04 05 18 2 v 1 3 1 M ay 2 00 4 Perfect random number generator is unnecessary for secure quantum key distribution

Quantum key distribution(QKD) makes it possible for two remotely separated parties do unconditionally secure communications. In principle, the security is guaranteed by the uncertainty principle in quantum mechanics: if any third party watches the key, she must disturbs the quantum bits therefore she has a risk to be detected. However, the security in practice is quite different, since many of the assumptions of the ideal case do not exist. Our presently existing secure proof of QKD protocols require the perfect random number generators. Actually, we can never have perfect generators in the real world. Here we show that the imperfect random numbers can also be used for secure QKD, if they satisfy certain explicit condition. Quantum key distribution(QKD) has abstracted strong interests of scientists since it makes it possible to set up unconditional secure key between two remote parties by principles of quantum mechanics. However, the unconditional security in principle does not necessarily give rise to the unconditional security in practice, where many non-ideal factors occur. “The most important question in quantum cryptography is to determine how secure it really is” [1]. Different from the assumed ideal situation, there are many imperfections in realizing ∗email: [email protected]