Security of classical noise-based cryptography

We examine security of a protocol on cryptographic key distribution viaclassical noise proposed by Yuen and Kim (Phys. Lett. A 241 135 (1998)).Theoretical and experimental analysis in terms of the secure key distributionrate shows that secure key distribution is possible even if the eavesdroppercould receive more photons than the legitimate receiver, as long as thesignal-to-noise-ratio (SNR) of the receiver is better than -9dB of theeavesdropper's SNR. Secure key distribution was demonstrated at the maximumrate of 0.04 bit per sender's bit and transmission rate of 2 Mb/s in theexperiment employing conventional fiber optics. The present protocol hasadvantages of the efficient key distribution and the simple implementation overother quantum key distribution protocols. However, careful design andmanagement are necessary to keep the security of the crypto-system