Can we consider PBFT (Practical Byzantine Fault Tolerance) as a consensus algorithm ?

And if yes, How does it work?

And is it similar to other consensuses such as PoW, PoS or PoA ? Or it is totally different?

And is it used actually in a blockchain platform? if yes, which one?

P.S. I heard that it is NOT scalable for large network, Is it true? And if so, is its scalability even worse than PoW?

  • You can't really compare the scalability. PoW scales perfectly with number of participants, but needs very long intervals between updates, and is inherently costly. PBFT only works with small numbers of participants, but can be much faster and cheaper. Sep 19, 2018 at 15:28
  • @Pieter Wuille Would you please explain in more details how PBFT works? Or any terse article which explains it briefly? Thank you
    – Questioner
    Sep 20, 2018 at 8:29

1 Answer 1


PBFT is Practical Byzantine Fault Tolerance. It is a "classical" consensus algorithm that uses a state machine. Uses leader and block election to select a leader.

PBFT is a three-phase, network-intensive algorithm (n^2 messages), so is not scalable to large networks

  • What do you mean by n^2 messages ? Is it time complexity? and "message" means "transactions" ? Thanks
    – Questioner
    Sep 20, 2018 at 9:07
  • 1
    It is a number of messages complexity, because every node must send messages to every other node. With 2 nodes, there are two messages, 3 nodes has 6 messages, 4 nodes have 12 messages, 5 nodes has 20 messages, 6 nodes has 30 messages, n nodes has n(n-1) messages. Sep 20, 2018 at 15:16
  • Thankk you, so it's n(n_1) messages, however, in your answer you have mentioned n power 2 (n^2), that's right? Thanks
    – Questioner
    Sep 20, 2018 at 15:24
  • 1
    Yes, in Big O notation O(n^2) is the same as (n * (n - 1)). In other words, it is exponential to the power of 2. The "- 1" makes little difference in the end. Sep 20, 2018 at 18:41
  • PBFT, in practice, scales for how many nodes? (Compared to Paxos and Raft. For example, HERE it's mentioned that Paxos does not scale for more than a dozen nodes. How about PBFT? ) Thanks.
    – Questioner
    Dec 3, 2021 at 12:12

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