# Practical, scalable algorithms for Byzantine agreement

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Please use this identifier to cite or link to this item: http://hdl.handle.net/1928/17495

# Practical, scalable algorithms for Byzantine agreement

 Title: Practical, scalable algorithms for Byzantine agreement Author: Oluwasanmi, Olumuyiwa Advisor(s): Saia, Jared Committee Member(s): Bridges, PatrickMoore, CristopherValerie, King Department: University of New Mexico. Dept. of Computer Science Subject: Byzantine AgreementFault-TolerantFault-ToleranceRandomized AlgorithmMonte CarloRandom BeaconDistributed AlgorithmConsensusByzantine LC Subject(s): Computer networks--Scalability.Fault-tolerant computing.Computer algorithms. Degree Level: Doctoral Abstract: With the growth of the Internet, there has been a push toward designing reliable algorithms that scale effectively in terms of latency, bandwidth and other computational resources. Scalability has been a serious problem especially with peer-to-peer (p2p) networks which may have sizes of more than a million nodes. An important problem in designing reliable algorithms is Byzantine agreement. For reasons of scalability, message complexity is a critical resource for this problem. Unfortunately, previous solutions to Byzantine agreement require each processor to send $O(n)$ messages, where $n$ is the total number of processors in the network. In this dissertation, we show that the Byzantine agreement problem can be solved with significantly less that a linear number of messages both in theory and in practice. We implement and test algorithms that solve the classical problem with each processor sending only $\tilde{O}(\sqrt{n})$ messages. Further, we consider the problem in the case where we assume the existence of a random beacon: a global source of random bits. We show that with this assumption, the required number of messages drops to $O(\log n)$, with small hidden constants. Our algorithms are Monte Carlo and succeed with high probability, that is probability $1-o(n^k)$ for some positive constant $k$. Our empirical results suggest that our algorithms may outperform classical solutions to Byzantine agreement for network of size larger than 30,000 nodes. Graduation Date: December 2011 URI: http://hdl.handle.net/1928/17495
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