Biblio

The blockchain technology revolution and the use of blockchains in various applications have resulted in many companies and programmers developing and customizing specific fit-for-purpose consensus algorithms. Security and performance are determined by the chosen consensus algorithm; hence, the reliability and security of these algorithms must be assured and tested, which requires an understanding of all the security assumptions that make such algorithms correct and byzantine fault-tolerant.This paper studies the "security ingredients" that enable a given consensus algorithm to achieve safety, liveness, and byzantine fault tolerance (BFT) in both permissioned and permissionless blockchain systems. The key contributions of this paper are the organization of these requirements and a new taxonomy that describes the requirements for security. The CAP Theorem is utilized to explain important tradeoffs between consistency and availability in consensus algorithm design, which are crucial depending on the specific application of a given algorithm. This topic has also been explored previously by De Angelis. However, this paper expands that prior explanation and dilemma of consistency vs. availability and then combines this with Buterin's Trilemma to complete the overall exposition of tradeoffs.

Protection of security-critical services, such as access-control reference monitors, is an important requirement in the modern era of distributed systems and services. The threat arises from hosting the service on a single server for a lengthy period of time, which allows the attacker to periodically enumerate the vulnerabilities of the service with respect to the server's configuration and launch targeted attacks on the service. In our work, we design and implement an efficient solution based on the moving "target" defense strategy, to protect security-critical services against such active adversaries. Specifically, we focus on implementing our solution for protecting the reference monitor service that enforces access control for users requesting access to sensitive resources. The key intuition of our approach is to increase the level of difficulty faced by the attacker to compromise a service by periodically moving the security-critical service among a group of heterogeneous servers. For this approach to be practically feasible, the movement of the service should be efficient and random, i.e., the attacker should not have a-priori information about the choice of the next server hosting the service. Towards this, we describe an efficient Byzantine fault-tolerant leader election protocol that achieves the desired security and performance objectives. We built a prototype implementation that moves the access control service randomly among a group of fifty servers within a time range of 250-440 ms. We show that our approach tolerates Byzantine behavior of servers, which ensures that a server under adversarial control has no additional advantage of being selected as the next active server.