Towards a secure and scalable blockchain protocol for data-intensive applications
Creators: name: Sohrabi, Nasrin
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 460605
subject: Distributed systems and algorithms
classificationCode: 460611
subject: Performance evaluation

description: Blockchain is an immutable decentralized database that facilitates the transparent and auditable management of data. It has formed the backbone of nearly every modern cryptocurrency that exists such as Bitcoin, Litecoin, Ethereum, and Hyperledger Fabric. It is anticipated that succeeding years will witness even more growth in the adoption of blockchain. This breakthrough technology is considered to have the potential to transform other sectors and offer them significant benefits; hence it has received increasing attention from academics and industry. There are two types of blockchain: permissioned and presmissionless. However, despite its advantages, blockchain still remains a novel technology that has room for improvements.

Studies show that the technology has serious limitations, namely, scalability, performance, and storage capacity. When comparing the performance figures of the blockchain- based cryptocurrencies with the centralized systems, such as Visa, the significant differ- ences between the two technologies become apparent. For instance, Visa can process over 2400 transactions per second, while Bitcoin and Ethereum can process around 7 and 20 transactions per second, respectively. When the number of transactions is increased, Bit- coin and Ethereum are not able to scale up and support the growth, while Visa can scale up and process up to 65000 transactions per second when needed. Clearly, these figures show the performance discrepancy between the two technologies.

Over the last decades, researchers have attempted to address these limitations to bring the technology to the level of maturity required for mainstream adoption. To address the shortcomings of blockchain, several solutions have been proposed such as Bitcoin- NG, ByzCoin, Elastico, Omniledger, IOTA, Ripple, Nano, Byteball, Hashgraph, Hotstuff, Rapidchain, Red Belly, and more. These works have focused on addressing the challenges that the technology poses for cryptocurrency applications, where blockchain has been used the most. Hence, these solutions have limited applicability as they are inappropriate for other sectors. Therefore, the fundamental issues still exist if blockchain is to be used in other sectors. Additionally, when previous works and the proposed solutions were closely examined, several drawbacks were identified. This motivated our research, which was conducted to address the fundamental challenges so that the technology can be adopted in sectors other than that of cryptocurrency.

We started our research by fist identifying the major metrics affecting the performance/scalability. Then, similar to other studies, we deconstructed blockchain into three core components: structure, consensus, and membership selection components. We studied the weaknesses of each component, categorised the existing solutions to each component is- sue, and examined the respective solutions. In the first part of the research, where we studied the structure component, we proposed a new structure called HTNZ which improved the performance of the original structure of the blockchain by a factor of 5. HTNZ modified the block structure by proposing two types of blocks, parentBlock and sideBlock. Additionally, it altered the chain structure to fit/store the sideBlocks. This is a two-dimensional storage model. That is, the chain grows from two dimension, one dimension is for the parentBlock, and the other dimension is the sideBlock chain.

In the second part of the research, we applied blockchain to a non-cryptocurrency con- text in order to more accurately identify the limitations of the technology for such applications, and also to learn their requirements. We focused on a security application, specifi- cally access control of outsourced data, and proposed a blockchain-based solution, BACC (Blockchain-Based Access Control). BACC is a decentralized access control model that enables cloud data centres to manage the access to the data stored on the cloud premises. We used Ethereum platform to implement BACC. Our analysis of BACC’s performance revealed that BACC performs poorly on the Ethereum platform and cannot perform as well as the current centralized approaches applied by cloud servers. When we integrated HTNZ structure in BACC, we noticed an improvement in performance although it was still less than that of the centralized models. Hence, more work was needed to address the issue successfully and efficiently.

Thus, in the next part of the research we focused on the consensus component of the blockchain and aimed to improve the performance/scalability further by modifying this component. We designed a novel consensus algorithm, SAZyzz (Scaling AZyzzyva), which has a better performances/scalability compared to the state-of-the-art BTF consensus algorithms applied in the existing blockchains. SAZyzz is built upon the AZyzzva algorithm. First, it relaxed the strong honest client assumption in AZyzzyva; and then applied a tree communication topology to improve the scalability. SAZyzz consists of a fast-path and a backup-path, each of which has two modes: simple mode and scalable mode.

Finally, in the last part of the research, we combined the newly-devised components, HTNZ and SAZyzz and proposed a new blockchain protocol, ZyConChain. We fully implemented ZyConChain in Java and conducted extensive experiments on the platform. The experimental results showed that ZyConChain has improved the performance/scalability significantly. To the best of our knowledge, this work is the first to address the limitations of blockchain in regard to non-cryptocurrency applications.