Foundations of Blockchains (Lecture 7.4: Proof of Liveness) скачать в хорошем качестве

Foundations of Blockchains (Lecture 7.4: Proof of Liveness)

A lecture series on the science and technology of blockchain protocols and the applications built on top of them, with an emphasis on fundamental principles. Full playlist:    • Foundations of Blockchains   Lecture 7: The Tendermint Consensus Protocol (5 videos) Lecture 7 notes: https://timroughgarden.github.io/fob2... Lecture 7 slides: https://timroughgarden.github.io/fob2... Leave comments/questions below or at   / 1531454337708343296   Lecture 7 tl;dr: 1. Lecture 6 showed that consistency and eventual (post-GST) liveness cannot be achieved by any SMR protocol in the partially synchronous model if f ≥ n/3. 2. The Tendermint protocol is a widely used consensus protocol that achieves consistency and eventual liveness provided f is less than n/3. 3. The first high-level idea in Tendermint is to carry out iterated single-shot consensus (with one consensus instance per block). 4. The second high-level idea is to restart after a timeout if there is insufficient progress due to a Byzantine block proposer or delayed messages. 5. The third high-level idea is to use two stages of voting to enable an intermediate outcome, between success and failure. 6. The Tendermint protocol uses rotating leaders, with one leader per round. 7. Each round has four phases: a block proposal phase (with the leader proposing); a first stage of voting (on the leader’s proposal); a second stage of voting (on the outcome of the first stage of voting); and a commit phase (for nodes that witnessed successful outcomes of both voting stages). 8. A voting stage is successful if a supermajority (two-thirds) of nodes all vote for the same block. Their votes constitute a quorum certificate (QC). 9. Tendermint satisfies consistency (when f is less than n/3) because an honest node commits to a block B only if it sees a successful second-stage vote, which happens only if more than n/3 honest nodes cast a first-stage vote for B. These honest nodes lock in on the block B and prevent the assembly of QCs for any blocks other than B. 10. Tendermint satisfies eventual liveness (when f is less than n/3) because, whenever there are two consecutive rounds post-GST with honest leaders, the second round concludes with all honest nodes committing a recently and honestly assembled block. 11. More recently developed consensus protocols use additional ideas to improve on the efficiency (e.g., latency, communication complexity, or responsiveness) of Tendermint without sacrificing optimal fault-tolerance in the partially synchronous model.