Last month, an altercation started between Charles Hoskinson of Cardano and Vitalik Buterin of Ethereum, which remains a never-ending argument to date. This heated argument began when Buterin questioned the competency of Cardano’s Ouroboros protocol.
Buterin had initially posted on Ethereum’s subreddit, a few points regarding the differences between Cardano’s Ouroboros and Ethereum’s Casper.
On 9th August, Charles Hoskinson shot a rebuttal on Twitter in response to Vitalik’s comment.
After Cardano’s first rebuttal blog post, Buterin responded with a post on Reddit. Part of his answer was in response to Hoskinson’s allegations that they were not aware of any publications or proof that sufficiently describes Casper’s mode of operation. He wrote:
“WTF? First of all, there is the Casper FFG paper. Second, there is the full FFG mini-spec. Both contain definitions of key guarantees (safety, plausible liveness, fairness…), along with proofs that they’re satisfied. In addition, there are computer-verified proofs of the properties of Casper FFG.”
He went on to further accuse that the protocol did not have any proof of correctness:
“The Ouroboros protocol is analyzed in a model that is fully described: it unambiguously defines all the participants’ programs, their execution and interactions, their communication – including network properties … Without such a model (notably missing in the Casper FFG white paper or in any other available sources related to Casper), it is impossible to prove the correctness of any claims about the protocol.”
On 13th August, Hoskinson took to Reddit to reply to Buterin’s previously posted accusations.
In continuation, last night [13th August], Buterin posted on Reddit, to respond to Hoskinson’s latest rebuttal:
“Answering this is easy and also showcases the importance of having concrete statements about protocols and proofs of their properties.”
Citing points in reference to theorem 1 of Ouroboros Genesis paper and theorem 9 of Ouroboros Praos Buterin wrote:
- For instance, consider a ten-fold increase in network delay. Plug in Delta and 10Delta in the alpha inequality and you will see that an extra factor approximately [1-f 9 Delta] will appear in the second case changing the lower bound for honest over active parties.
- For the sake of concrete numbers, suppose f originally is set as f*Delta ~< 0.03; in turn, this means that the protocol will provide security in the 10Delta setting assuming the honest parties are over at least 69%, as opposed to over ~50%
- So 1/f is the “average block time” (roughly), Delta is the network latency, so when Delta >= 1/f * ln(2) (ie. network latency exceeds block time multiplied by >= 0.693), (1-f)Delta <= 1/2, so you can’t prove any level of security at all.
In relation to the above points, Buterin feels that a security assumption is being made. He said:
“To me, that feels like you are making a security assumption that Delta < 1/f * ln(2) in order to get any guaranteed safety/liveness at all, and so it would be most accurate to call the algorithm synchronous. Or is there something I’m still missing here?”
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