Communication With Adversary Identification in Byzantine Multiple Access Channels

TL;DR

This paper studies how to identify malicious users in a noisy communication system with two users, focusing on detecting deviations that affect message decoding, and provides capacity bounds for such channels.

Contribution

It introduces a new problem formulation for identifying adversaries in Byzantine multiple access channels and characterizes the feasible channels with bounds on capacity regions.

Findings

Characterization of channels where communication and identification are feasible.

Inner and outer bounds on the capacity region for the problem.

Conditions under which deviations can be reliably detected or tolerated.

Abstract

We introduce the problem of determining the identity of a byzantine user (internal adversary) in a communication system. We consider a two-user discrete memoryless multiple access channel where either user may deviate from the prescribed behaviour. Owing to the noisy nature of the channel, it may be overly restrictive to attempt to detect all deviations. In our formulation, we only require detecting deviations which impede the decoding of the non-deviating user's message. When neither user deviates, correct decoding is required. When one user deviates, the decoder must either output a pair of messages of which the message of the non-deviating user is correct or identify the deviating user. The users and the receiver do not share any randomness. The results include a characterization of the set of channels where communication is feasible, and an inner and outer bound on the capacity region.