Classifying Trusted Hardware via Unidirectional Communication

TL;DR

This paper investigates the power of different trusted hardware modules in Byzantine fault-tolerant systems, introducing the concept of unidirectionality to distinguish their capabilities in preventing network partitions.

Contribution

It introduces the notion of unidirectionality to classify trusted hardware modules and demonstrates that shared-memory modules provide this property, unlike others.

Findings

Shared-memory hardware modules provide unidirectionality.

Non-shared-memory modules do not provide unidirectionality.

Unidirectionality helps distinguish the power of trusted hardware modules.

Abstract

It is well known that Byzantine fault tolerant (BFT) consensus cannot be solved in the classic asynchronous message passing model when one-third or more of the processes may be faulty. Since many modern applications require higher fault tolerance, this bound has been circumvented by introducing non-equivocation mechanisms that prevent Byzantine processes from sending conflicting messages to other processes. The use of trusted hardware is a way to implement non-equivocation. Several different trusted hardware modules have been considered in the literature. In this paper, we study whether all trusted hardware modules are equivalent in the power that they provide to a system. We show that while they do all prevent equivocation, we can partition trusted hardware modules into two different power classes; those that employ shared memory primitives, and those that do not. We separate these classes using a new notion we call unidirectionality, which describes a useful guarantee on the ability of processes to prevent network partitions. We show that shared-memory based hardware primitives provide unidirectionality, while others do not.