Asynchronous Byzantine Reliable Broadcast With a Message Adversary

TL;DR

This paper introduces a reliable broadcast algorithm for asynchronous systems that tolerates Byzantine faults and message adversaries, achieving optimal efficiency when no message adversary is present.

Contribution

It presents a new reliable broadcast algorithm that handles both Byzantine processes and message adversaries, establishing the necessary conditions for such systems.

Findings

Algorithm terminates in two steps when no message adversary exists.

The condition n > 3t + 2d is necessary for reliable broadcast under combined adversaries.

The algorithm is optimal in time efficiency without message adversaries.

Abstract

This paper considers the problem of reliable broadcast in asynchronous authenticated systems, in which n processes communicate using signed messages and up to t processes may behave arbitrarily (Byzantine processes). In addition, for each message m broadcast by a correct (i.e., non-Byzantine) process, a message adversary may prevent up to d correct processes from receiving m. (This message adversary captures network failures such as transient disconnections, silent churn, or message losses.) Considering such a "double" adversarial context and assuming n > 3t + 2d, a reliable broadcast algorithm is presented. Interestingly, when there is no message adversary (i.e., d = 0), the algorithm terminates in two communication steps (so, in this case, this algorithm is optimal in terms of both Byzantine tolerance and time efficiency). It is then shown that the condition n > 3t + 2d is necessary for implementing reliable broadcast in the presence of both Byzantine processes and a message adversary (whether the underlying system is enriched with signatures or not).