# Guessing probability under unlimited known-plaintext attack on secret keys for Y00 quantum stream cipher by quantum multiple hypotheses testing

## TL;DR

This paper evaluates the security of the Y00 quantum stream cipher against unlimited known-plaintext attacks, showing that the guessing probability of secret keys remains below 1, thus providing new insights into its security.

## Contribution

It introduces a novel method using quantum multiple hypotheses testing to assess the guessing probability of secret keys in Y00, a previously unstudied aspect.

## Key findings

- Guessing probability remains below 1 even with unlimited known plaintext.
- First application of quantum multiple hypotheses testing to Y00 security analysis.
- Provides insights for future security evaluations of quantum communication protocols.

## Abstract

Although quantum key distribution is regarded as promising secure communication, security of Y00 protocol proposed by Yuen in 2000 for the affinity to conventional optical communication is not well-understood yet; its security has been evaluated only by the eavesdropper's error probabilities of detecting individual signals or masking size, the number of hidden signal levels under quantum and classical noise. Our study is the first challenge of evaluating the guessing probabilities on shared secret keys for pseudorandom number generators in a simplified Y00 communication system based on quantum multiple hypotheses testing theory. The result is that even unlimitedly long known-plaintext attack only lets the eavesdropper guess the shared secret keys of limited lengths with a probability strictly < 1. This study will give some insights for detailed future works on this quantum communication protocol.

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Source: https://tomesphere.com/paper/1812.04738