CCE Theses and Dissertations

Date of Award

2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy Cybersecurity Management

Department

College of Computing and Engineering

Advisor

Gregory Simco

Committee Member

Francisco Mitropoulos

Committee Member

Sumitra Mukherjee

Committee Member

Michael Lehrfeld

Keywords

Asynchronous Systems, Blockchain, Consensus Algorithms, Distributed Systems, Fault Tolerance, Permissionless Systems

Abstract

Asynchronous consensus protocols are essential for decentralized and trustless environments such as decentralized finance (DeFi), supply chain management, and voting systems. These protocols eliminate centralized authority and timing assumptions while improving resilience and security. However, as network sizes increase the communication overhead in these systems becomes a bottleneck that limits scalability and efficiency. One notable example is the Aleph protocol, which stands out as one of the first consensus protocols to be both asynchronous and permissionless while providing Byzantine Fault Tolerance. Unlike many existing asynchronous consensus mechanisms, Aleph is permissionless in nature and does not rely on a trusted dealer or predefined set of participants, making it well-suited for fully decentralized blockchain applications. Its permissionless and asynchronous nature allows it to function without synchronized clocks or fixed membership ensuring greater fault-tolerance and robustness in adversarial conditions. These are key properties for blockchain networks that operate in open dynamic environments. Regarding the blockchain trilemma, this design strengthens decentralization and security but also introduces higher communication complexity which impacts scalability. This research acknowledged these trade-offs and enhanced asynchronous permissionless consensus by reducing communication overhead making it more scalable for decentralized applications.

Aleph’s consensus mechanism relies on a Chain Reliable Broadcast (ch-RBC) protocol for message dissemination. Despite its advantages the ch-RBC suffers from quadratic communication complexity leading to substantial overhead in large networks. This dissertation proposed an enhancement to Aleph’s ch-RBC protocol by replacing its Merkle tree-based transaction validation with Rivest-Shamir-Adleman (RSA) accumulators. The research succeeded in reducing the protocol’s communication complexity from O(Tr + N² log N) to O(Tr + N²), thereby improving performance and scalability while maintaining security guarantees. RSA accumulators offer compact and constant-sized proofs for transaction validation which can significantly reduce message complexity and bandwidth consumption.

The study employed an experimental approach by implementing both the original Merkle tree-based ch-RBC and the RSA accumulator-based version. Simulations were conducted using Rust-based implementations on AWS EC2 instances with network sizes ranging from 5 to 104 nodes and transaction batch sizes scaling up to 1024 transactions per round. Key performance metrics were transaction throughput, latency, communication overhead, and resource utilization.

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