3 ms·

While proof of stake does have a lot of advantages over PoW, it cannot handle more than 1/3 of the voiting power acting incorrectly. This is a well known hard b

While proof of stake does have a lot of advantages over PoW, it cannot handle more than 1/3 of the voiting power acting incorrectly. This is a well known hard bound on BFT algorithms. In terms of implementing PoS, most BFT algos have traditionally scaled poorly (HotStuff which is linear in communication costs relative to the number of nodes/validators is very recent). In addition, going offline for validators, even accidentally, hurts the network and slashing PoS schemes often have uptime requirements. Validators also need to have the infra to be hidden and not DDOS'd. tl;dr, Proof of stake is still decently centralized, but a lot of work is being done to scale it.

narush 7y ago
The 1/3 bound is for general byzantine behavior. If you're willing to get more specific about the type of behavior you want to tolerate, the bounds are more flexible[1] (this link is from the HotStuff people, actually!). For example, a node could tolerate no more than "20% Byzantine faults and 30% alive-but-corrupt faults" In turn, this allows different clients to make different assumptions (one huge advantage PoW has over traditional BFT protocols). Also, w.r.t. linear communication, CBC Casper[2] has the ability to come to consensus on a blockchain with, in the limit (and in the optimal case), a single message per block that is finalized. It uses essentially the same form of pipelining that HotStuff does, but to the extreme (at at the cost of a much longer time for blocks to be finalized). Full disclosure: I work on CBC Casper, so take what I'm saying with a grain of salt. [1] https://dahliamalkhi.wordpress.com/2019/04/24/flexible-byzantine-fault-tolerance/ https://dahliamalkhi.wordpress.com/2019/04/24/flexible-byzan... [2] https://github.com/cbc-casper/cbc-casper-paper/blob/master/cbc-casper-paper-draft.pdf https://github.com/cbc-casper/cbc-casper-paper/blob/master/c...
- trianglesphere 7y ago
  Good point with the flexible BFT paper. I didn't realize casper pipelines, I'll have to look into it. I'm working on IBFT (fixed to be more pbft like).
zodiac 7y ago
> While proof of stake does have a lot of advantages over PoW, it cannot handle more than 1/3 of the voiting power acting incorrectly. The 1/3 bound is without any synchronicity assumptions; with strong synchronicity assumptions you can get to 1/2. This seems strictly better than PoW (no liveness at all in an asynchronous network, and 1/2 with synchronicity assumptions).

narush 7y ago

The 1/3 bound is for general byzantine behavior. If you're willing to get more specific about the type of behavior you want to tolerate, the bounds are more flexible[1] (this link is from the HotStuff people, actually!). For example, a node could tolerate no more than "20% Byzantine faults and 30% alive-but-corrupt faults" In turn, this allows different clients to make different assumptions (one huge advantage PoW has over traditional BFT protocols). Also, w.r.t. linear communication, CBC Casper[2] has the ability to come to consensus on a blockchain with, in the limit (and in the optimal case), a single message per block that is finalized. It uses essentially the same form of pipelining that HotStuff does, but to the extreme (at at the cost of a much longer time for blocks to be finalized). Full disclosure: I work on CBC Casper, so take what I'm saying with a grain of salt. [1] https://dahliamalkhi.wordpress.com/2019/04/24/flexible-byzantine-fault-tolerance/ https://dahliamalkhi.wordpress.com/2019/04/24/flexible-byzan... [2] https://github.com/cbc-casper/cbc-casper-paper/blob/master/cbc-casper-paper-draft.pdf https://github.com/cbc-casper/cbc-casper-paper/blob/master/c...

trianglesphere 7y ago
Good point with the flexible BFT paper. I didn't realize casper pipelines, I'll have to look into it. I'm working on IBFT (fixed to be more pbft like).

zodiac 7y ago

> While proof of stake does have a lot of advantages over PoW, it cannot handle more than 1/3 of the voiting power acting incorrectly. The 1/3 bound is without any synchronicity assumptions; with strong synchronicity assumptions you can get to 1/2. This seems strictly better than PoW (no liveness at all in an asynchronous network, and 1/2 with synchronicity assumptions).