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Executive Summary
- We introduce the key points of “Scaling Blockchains: Can Elected Committees Help?” (referred to as the ‘paper’ in this report) by Alon Benhaim, Brett Hemenway Falk, and Gerry Tsoukalas.
- In ‘committee-based consensus’, voters delegate to a small committee the rights to produce and certify blocks.
- Often associated with Delegated Proof of Stake (DPoS) systems, stake-weighted voters elect a small group of block producers as a committee responsible for producing and validating blocks.
- Most DPoS systems adopt approval voting, where each stake-holding voter “approves” preferred candidates to join the committee.
- The paper lays out a model where a blockchain’s token holders vote to elect a committee of block producers according to an up-to-t, k-winner approval voting system; t is the maximum number of candidates each voter can vote for, and k indicates the candidates with the highest scores.
- The goal of the model is to seek an optimal strategy to maximise the probability of electing an honest committee.
- Data collected from EOS is used as empirical observations to analyse the real-world voting strategies.
- There are two particular voting strategies illustrated: threshold voting and cardinal voting.
- In the model:
- The authors derive the formula to calculate the objective function of the optimisation, which is the probability that an elected committee is honest.
- The voters’ behaviour dramatically depends on the low vs. high number of voters.
- The probability of success rapidly and exponentially converges to 100% when the signals are deemed not entirely uninformative.
- The minimum committee size required to achieve a failure probability is much smaller for the DPoS-like system compared with the randomly chosen committee (as in Algorand).
- The paper also illustrates the problems of approval voting:
- One drawback of electing committees, compared to selecting random committees, is that elections seem to lead to stagnation.
- A small, static set of block producers reduces decentralisation — the core tenet of blockchains and cryptocurrencies.
Read the full scholar article here: A Discussion on Efficiency and Security for Committee-Based Consensus Protocols
