Immunity against Correlation Attack on Quantum Stream Cipher by Yuen 2000 Protocol

摘要

This paper presents the security analysis on the quantum stream cipher so called Yuen-2000 protocol (or αη scheme) against the fast correlation attack, the typical attack on stream ciphers. Although the security of a very simple experimental model of the quantum stream cipher without a randomization may be reduced to a complexity based security against the correlation attacks under a large number of known plaintexts, it is not a basic feature of Yuen 2000 protocol. In fact, we clarify that there exists a randomization scheme which attains the perfect correlation immunity against such attacks under an approximation. And in this scheme, the running key correlation from the second randomization that determines the mapping patterns is broken off also by quantum noise. In such a case, any fast correlation attack does not work on the quantum stream cipher.