On May 19th, Harmony co-founder & CTO Rongjian Lan published an article “Harmony’s Staking and Incentive Design” to introduce Consensus Leader Rotation, stating the following:
Harmony is a Proof-of-Stake blockchain with a sharded network where each shard contains a large group of validators (~400 at initial mainnet launch). Validators validate new blocks and vote to reach consensus using our FBFT algorithm where a 2/3 quorum of votes is needed for consensus.
To be able to vote, validators need to have voting shares bonded to them. One bonded voting share grants one vote for a validator to cast in the FBFT consensus. A voting share will stay bonded to a validator for the bonding period of 7 epochs. After the bonding period ends, the voting share will be released and be available to re-bond. For each shard, there will be roughly 400 bonded voting shares used for consensus.
“We only allow one voting share per validator address. Thus, each shard will have around 400 validators. At the start of a new epoch, the validators are randomly permuted based on the randomness from the DRG protocol and forms a random sequence. Starting from the first position of the sequence, the validators take turns to be the leader for FBFT consensus and each validator stays as the leader for 40 blocks. Given our epoch time of 16384 blocks and an estimated 5s block interval, this setup ensures that each validator will have one chance of being the leader during an epoch,” as he detailed in the article.
Then on July 9th, Vitalik Buterin the founder of Ethereum read the article and post a question: “Doesn’t this mean that if a single validator is malicious they could delay the inclusion of any transaction for 40 blocks? (I don’t mean by going offline, I mean by censoring) Or am I not understanding correctly?"
Rongjian responded to him and wrote: “The answer to your question is yes given the content only in this doc. But mitigation can be applied such as 1) allowing validators to preempt the leader if more than 2/3 of them detected that certain transactions were not included for k blocks (e.g. k=4); 2) adjusting the parameter of 40 to a lower number to basically trade potential system downtime with resistance to potential censorship. After all, a certain degree of censorship exists in most of the blockchains including Bitcoin and Ethereum. It’s hard to achieve 100% censorship resistant without making the system too complicated or introducing inconveniences to the users.”
Just an hour later, Vitalik commented to the response: “Interesting! I’ve thought before about using non-censorship of transactions as a soft validity condition for blocks, but my conclusion has generally been that it would lead to too much network instability if there’s disagreement about what txs have been published. But using censorship detection as an input to vote on view changes is an interesting approach!”
Since the foundation of Harmony, one of our main goals was to be as transparent as possible in releasing information to the public. We have always outlined our new technology and research in articles, allowing everyone to dive into our innovations.
Research director of Cosmos, Zaki Manian, commented on Twitter on June 9th, “as far as I can tell, Harmony is the first blockchain with functional PBFT view change.”
FBFT, Fast-BFT consensus is another important innovation of Harmony. Harmony’s Fast-BFT combines the battle-tested PBFT algorithm with cutting edge BLS multisignatures to deliver a scalable and secure consensus algorithm. This transforms the slow but very secure PBFT consensus, making it orders of magnitude faster. Best of all, FBFT guarantees finality within just one block confirmation.
Harmony’s consensus protocol,FBFT, an improvement on PBFT has been mentioned by Zaki himself in how it is the, “first blockchain with functional PBFT view change.” This has garnered so much interest that Vitalik himself has been talking about the “Leader Rotation” mechanism.
Not only has Cardano’s CEO, Charles Hoskinson, been highly complimenting Harmony’s white paper, but also on how it brings people together to one of the most active research and development in the community.
We look forward to working with the not just the tech community but the whole crypto community to innovate and overcome the issue of scalability in blockchain so we can all step into the real adoption phase.