Universal coding for transmission of private information

TL;DR

This paper introduces a universal coding scheme for private classical communication over classical-quantum channels, ensuring reliable transmission to Bob while keeping information secret from Eve without needing detailed channel knowledge.

Contribution

It proves the existence of a universal coding scheme that guarantees privacy and reliability without specific channel knowledge, relying only on input distribution and Holevo quantity bounds.

Findings

Universal code exists for private classical communication

Code guarantees reliable transmission to Bob

Eavesdropper learns nothing about messages

Abstract

We consider the scenario in which Alice transmits private classical messages to Bob via a classical-quantum channel, part of whose output is intercepted by an eavesdropper, Eve. We prove the existence of a universal coding scheme under which Alice's messages can be inferred correctly by Bob, and yet Eve learns nothing about them. The code is universal in the sense that it does not depend on specific knowledge of the channel. Prior knowledge of the probability distribution on the input alphabet of the channel, and bounds on the corresponding Holevo quantities of the output ensembles at Bob's and Eve's end suffice.