Has a consensus algorithm where temporary authorities are fairly “elected” via PoW been discussed? In the usual proof-of-work consensus system, miners constantly compute hashes (“wasting” resources). What if hashing were restricted to a certain time window, e.g., 1 hour per day?

This could act as a leader election for the remainder of the day. These leaders are “representative” of the entire network since they’re sampled using PoW.

The leaders could then use some Byzantine fault tolerant consensus algorithm to decide what blocks to append — without mining — until their “term” is up.

Has such a system — or something (even vaguely) similar — already been discussed?




The obvious question is how vulnerable this system is to colluding attackers. (Clearly it is weaker than the usual “51%” majority rule, but exactly how bad is it?)

If we assume that the BFT consensus algorithm can tolerate a fraction of 1/3 bad leaders, we can calculate the probability of a successful attack as a function of the bad PoW capacity share using some binomial distribution maths. Some back-of-the-envelope Python calculations suggest that perhaps 20% bad PoW share is tolerable, which isn’t absolutely terrible.
Maybe there is no known BFT consensus algorithm that would scale to anything close to the Bitcoin network (e.g., in PBFT the number of “replicas”, i.e., leaders, is &lt;&lt; 100).


I’m sure there are plenty of other potential problems, I’m just wondering if it is feasible at all. Perhaps it has been discussed in some other context.
I’ve since found several related concepts in research papers or coin protocol proposals:


Bitcoin-NG separates leader election (key block) and the following “election term” (epoch), in which microblocks are freely added by the leader.
Tendermint (and, before it, Hyperledger) uses BFT consensus (but with PoS as the basis for elections).
Building upon the previous, ByzCoin elects leaders via PoW and uses PBFT to agree on the microblocks.


The article The Road to Scalable Blockchain Designs gives a good intro to and context for ByzCoin. Exploring the citation graph of the ByzCoin paper leads to further similar work at ETHZ and Cornell as “hybrid consensus” or a “strongly consistent” blockchain.

None of these use the energy-savings aspect that motivated me; instead they all aim at improving throughput and/or transaction verification time. But the “PoW leader election + BFT consensus” concept seems to be pretty actively researched.