Byzantine-tolerant algorithm reduces message overhead in distributed networks
Byzantine-Tolerant Causal Unicast with Constant Message Space Overhead
Distributed, Parallel, and Cluster ComputingData Structures and Algorithms
Summary
Ensuring messages arrive in the right order across unreliable computer networks is very hard, especially when some participants might behave maliciously. Previous methods to handle these problems required a lot of message storage or made timing assumptions. The authors developed a new approach that keeps message storage constant no matter how many participants there are, sorts messages nearly correctly, and prevents certain attacks that stall communication. Their method balances safety, speed, and memory use with proven guarantees, though it allows some exceptions under extreme network problems or attacks.
What this means in practice
- •For distributed system engineers: Build communication protocols that maintain causal message order with minimal memory use even if some nodes act maliciously.
- •For network security teams: Deploy messaging layers resilient to attacks that delay or block messages by isolating message buffers per connection and evicting stale data.
Authors
Purv Patel, Ajay D. Kshemkalyani
Abstract
Causal message ordering provides essential semantics for distributed applications, yet ensuring it within an asynchronous system subject to Byzantine failures presents fundamental theoretical and practical challenges. Prior research establishes that algorithms cannot guarantee both strong safety and liveness without using cryptography under these conditions. Existing Byzantine-tolerant solutions make synchrony assumptions or suffer from $O(n)$ message space overheads and $O(n^2)$ message complexity, where $n$ is the number of processes in the system, or use cryptography, but may not guarantee strong safety. In this paper, we present a novel Byzantine-tolerant causal ordering algorithm that achieves an optimal $O(1)$ application message space overhead for point-to-point messages. Our approach uses a Sender Permission to Send (SPS) invariant and an \textit{Isolated-Buffer Optimistic Model} for the memory management architecture. To circumvent Byzantine state-pinning and head-of-line blocking attacks, instead of unified causal buffers, we use isolated, per-peer queues equipped with event-driven \textit{Cascading Space Evictions}. We formally prove that our algorithm guarantees system-wide liveness and satisfies a weakened causal safety abstraction called \textit{Congestion-Relaxed Causal Delivery}. Under this model, weak causal safety is strictly preserved for all honest-to-honest communications unless extreme network latency or Byzantine withholding attacks exceed quantifiable local buffer capacities, forcing optimistic queue evictions. This formal guarantee successfully balances causal ordering with high throughput, constant message space overhead, low computational overhead, and strictly bounded local space.