Probability Distribution Model to Analyze the Trade-off between Scalability and Security of Sharding-Based Blockchain Networks

Sharding is considered to be the most promising solution to overcome and to improve the scalability limitations of blockchain networks. By doing this, the transaction throughput increases, at the same time compromises the security of blockchain networks. In this paper, a probability distribution model is proposed to analyze this trade-off between scalability and security of sharding-based blockchain networks. For this purpose hypergeometric distribution and Chebyshev's Inequality are mainly used. The upper bounds of hypergeometric distributed transaction processing and failure probabilities for shards are mainly evaluated. The model validation is accomplished with Class A (Omniledger, Elastico, Harmony, and Zilliqa), and Class B (RapidChain) sharding protocols. This validation shows that Class B protocols have a better performance compared to Class A protocols. The proposed model observes the transaction processing and failure probabilities are increased when shard size is reduced or the number of shards increased in sharding-based blockchain networks. This trade-off between the scalability and the security decides on the shard size of the blockchain network based on the real-world application and the blockchain platform. This explains the scalability trilemma in blockchain networks claiming that decentralization, scalability, and security cannot be met at primary grounds. In conclusion, this paper presents a comprehensive analysis providing essential directions to develop sharding protocols in the future to enhance the performance and the best-cost benefit of sharing-based blockchains by improving the scalability and the security at the same time.

I. Introduction

Blockchain has been adapted to almost every industry such as banking, multimedia [1], and health sector today from the technology of Bitcoin, which was introduced by Satoshi Nakamoto in 2008 [2]. Blockchain technology is a peer-to-peer architecture simply explained as chains of blocks, where each block contains information of a single transaction in a network. The core idea of this technology is to decentralize transactions in an immutable and chronological manner without depending on a central trusted computer. Every node in this decentralized database ledger represents a data server in the network in a transparent and unalterable manner through cryptographic hashing. The Proof-of-Work consensus used in blockchain technology ensures that newly generated nodes in the network verified by all current nodes in the network [3]. This mechanism verifies that blocks do not tamper; at the same time, increases the latency that affects the transaction throughput. In Bitcoin technology, this process takes approximately ten minutes [2]. This motivates the importance of scaling up the blockchain network to address the latency issues and to increase the transaction throughput. A recent study by [4] introduced different mechanisms like utilizing the block size, processing off-chain transactions, and on-chain mechanisms like sharding for this purpose. From these methods, sharding is considered to be the most promising method to improve the scalability in blockchain networks.