Robust Proof of Stake: A New Consensus Protocol for Sustainable Blockchain Systems
2. Literature Review
3. The Proposed Comparison Framework and Two Consensus Protocols
3.1. The Proposed Framework
- Energy-saving. With rapid economic development, a large amount of energy consumption result in a large amount of carbon dioxide emissions, which has significantly changed the global climate and seriously affected the living environment of human beings. Therefore, it is crucial to design a distributed economy system with low energy conservation and carbon dioxide emission . This is why most of the papers in Table 1 considered the dimension of energy-saving.
- Robustness. As mentioned in the Introduction section, blockchain systems are also under many types of cyber-attacks, such as the DAO attack  and random number attack , which became a huge threat to the stable and sustainable development of blockchain systems . Hence, many frameworks in Table 1 considered the related dimensions such as robustness  and error-tolerant rate .
- TPS. TPS is an important indicator to measure the efficiency of a financial system, as it represents the transaction volume completed by the system per second . Alibaba’s Alipay carried a world record 256,000 TPS for 5 minutes and 22 seconds on 11 Nov 2017, and VISA can handle on average around 1700 TPS . In contrast, the well-known blockchain systems (such as Bitcoin and Ethereum) can only reach less than 40 TPS, making them impossible to manage the transaction volume in the real world . Therefore, we see that Han et al.  and Bach et al.  included the TPS in their frameworks.
- Trade request-satisfied ratio. A blockchain system can be viewed as a trade network among autonomous traders who have the request to either buy, sell or hold coin. Unlike the stock market, traders in the blockchain system have no central counter party which provides clearing and settlement services. The ones who want to buy or sell coins need to find the trade partner to fulfill their demands. Hence, the trade request-satisfied ratio is defined as the division of total satisfied coin requests by total coin requests . The larger the ratio is, the higher the trade request-satisfied ratio of a blockchain system is.
3.2. PoW, Proof of Work Protocol
3.3. PoS, Proof of Stake Protocol
4. The RPoS Consensus Protocol
4.1. RpoS Consensus Protocol
- Dynamic coin age. As there are too many mining nodes, we propose the concept of “dynamic coin age”, which serves as a threshold. Only the node which meets this coin age condition (the coin age is defined in Formula (3)) can compete for the packing chance, and get the system reward.
- Calculation of coin age. Before calculating the coin age of the node, we first compute the accumulation of time and the number of coins. Each block has a timestamp, and the accumulated time can be obtained by the timestamp, that is,
- RPoS mining process. The definition of the target value is a value that is dynamically adjusted according to the block production time, and is used to identify the difficulty of the block production; we define it in Formula (4).
4.2. RpoS Consensus Protocol Implementation
5. Comparison of the Three Consensus Protocols
5.1. Theoretical Comparison
- Power consumption. In PoW systems, miners consume a lot of power to compete for packing opportunities using a large number of mining machines, making the system energy-intensive and unsustainable. As mentioned in Section 3, the Bitcoin system consumes more energy than the entire nation of Switzerland . Hence, the power consumption of PoW is high in Table 2. In PoS systems, miners rely on the stake (the amount of coins held and coin age) for packing competition, and the power consumption of PoS is low in Table 2, which is much more energy-saving and sustainable than PoW. In RPoS systems, miners compete for packing opportunity based on the amount of coins. Similar to PoS, without using mining machines, the power consumption of RPoS is also low in Table 2. Hence, both PoS and RPoS have the advantage over PoW in terms of energy-saving.
- Robustness. PoW systems (taking the Bitcoin system as an example) are becoming increasingly centralized due to a small number of mining pools, leading to a high risk of 51% attack in the system . Hence, PoW systems often have low robustness, as we indicated in Table 2. The weaknesses of PoS systems are coin age accumulation attack and [email protected] attack, as we introduced in Section 3.3. Hence, PoS faces high risk of these two attacks as in Table 2. This motivated us to propose RPoS, making the blockchain system robust against these attacks. RPoS uses the amount of coins to compete for packing opportunities, instead of coin age, so there is almost no risk of coin age accumulation attack and [email protected] attack in the system. PoW, of course, is immune (not applicable, n/a) to these PoS attacks as it does not have the concept of stake. Meanwhile, rational nodes in PoS and RPoS systems will not launch 51% attack because their payoff will be negative . Hence, we suggest that the risk of 51% attack in PoS and RPoS systems is low.
- TPS. The TPS of PoW system is about 7, and the TPS of PoS system is 30-40, which is more efficient than PoW . RPoS protocol is a PoS-based protocol which removed the process of currency age selection and clearing, hence it is very likely that RPoS should be faster than PoS.
5.2. Simulation Comparison
5.2.1. Assumptions and Settings in the Agent-based Model
5.2.2. Simulation Design
5.2.3. Results and Discussion
Conflicts of Interest
|RpoS||Robust Proof of Stake||The proposed consensus protocol for blockchain system|
|PoW||Proof of Work||The first consensus protocol for blockchain system|
|PoS||Proof of Stake||A popular consensus protocol for blockchain system|
|P2P||Peer to Peer||A distributed application architecture that partitions tasks between peers|
|ETH||Ether||A blockchain system based on PoW and PoS|
|EOS||Enterprise Operation System||A blockchain system based on Delegated PoS|
|DApp||Decentralized Application||Application in decentralized blockchain systems|
|RPCA||Ripple Consensus Algorithm||A consensus protocol for blockchain system|
|BFT||Byzantine Fault Tolerance||A consensus protocol for blockchain system|
|ABMS||Agent-based Modeling and Simulation||A research method to understand agent interactions|
|[email protected]||Nothing-at-Stake||A type of attack which can happen in PoS blockchain system|
|TPS||Transaction Per Second||An index to describe the trade efficiency of a financial system|
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|Papers||Considered Dimensions||Research Method|
|Saleh ||energy-saving, robustness||qualitative research and game theoretical analysis|
|Han et al. ||energy-saving, efficiency, coherence, error-tolerant rate, extensibility||qualitative research and quantitative research|
|Zhou ||energy-saving, computing power distribution||qualitative research and|
|Wei et al. ||coin price index, request-satisfied ratio, Gini index||agent-based modeling and simulation|
|Bach et al. ||energy-saving, tolerated power of adversary, TPS, market capitalization||qualitative research and quantitative research|
|Coin age accumulation attack||n/a||high||low|
|[email protected] attack||n/a||high||low|
|Transactions Per Second (TPS)||~7||30-40||>40|
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Li, A.; Wei, X.; He, Z. Robust Proof of Stake: A New Consensus Protocol for Sustainable Blockchain Systems. Sustainability 2020, 12, 2824. https://doi.org/10.3390/su12072824
Li A, Wei X, He Z. Robust Proof of Stake: A New Consensus Protocol for Sustainable Blockchain Systems. Sustainability. 2020; 12(7):2824. https://doi.org/10.3390/su12072824Chicago/Turabian Style
Li, Aiya, Xianhua Wei, and Zhou He. 2020. "Robust Proof of Stake: A New Consensus Protocol for Sustainable Blockchain Systems" Sustainability 12, no. 7: 2824. https://doi.org/10.3390/su12072824