# Asymmetric Distributed Trust

## TL;DR

This paper introduces asymmetric Byzantine quorum systems that allow processes to have subjective trust, generalizing standard models and enabling new protocols for shared memory, broadcast, and consensus in Byzantine environments.

## Contribution

It presents the concept of asymmetric trust in quorum systems and develops protocols that support this model, expanding the capabilities of fault-tolerant distributed computing.

## Key findings

- Asymmetric quorum systems model subjective trust among processes.
- Protocols for shared memory, broadcast, and consensus are developed under asymmetric trust.
- The model enables more flexible and realistic trust assumptions in distributed systems.

## Abstract

Quorum systems are a key abstraction in distributed fault-tolerant computing for capturing trust assumptions. They can be found at the core of many algorithms for implementing reliable broadcasts, shared memory, consensus and other problems. This paper introduces asymmetric Byzantine quorum systems that model subjective trust. Every process is free to choose which combinations of other processes it trusts and which ones it considers faulty. Asymmetric quorum systems strictly generalize standard Byzantine quorum systems, which have only one global trust assumption for all processes. This work also presents protocols that implement abstractions of shared memory, broadcast primitives, and a consensus protocol among processes prone to Byzantine faults and asymmetric trust. The model and protocols pave the way for realizing more elaborate algorithms with asymmetric trust.