On 13/12/14 04:04, Alex Mizrahi wrote: > Well, client-side validation is mathematically secure, while SPV is > economically secure. > I.e. it is secure if you make several assumptions about economics of the > whole thing.
Comparisons with the SPV security of sidechains are fallacious. The alternative to a proof-of-publication system reliant on client-side validation is a blockchain. The question of whether the token used on said blockchain should be two-way-pegged to BTC is completely orthogonal. (ie. yes, sidechains are "economically secure", in that you're reduced to balancing economic incentives to avoid peg theft. But sidechains also give us something unique in return - the ability to innovate without needing to start new artificial scarcity races. Nothing else can do that.) <snip> > You know, The Great Fork of 2013 was resolved through human > intervention, Bitcoin nodes were not smart enough to detect that > something is going awry on their own. I hate to think what the outcome would've been on a proof-of-publication system. You don't even have a fork. You just have a whole bunch of nodes who sort-of-mostly agree on a shared history, except where they don't. Maybe they just disagree on the validity of a single transaction. They'll slowly diverge over time (as bad transactions are used as input to other transactions.) You have no reliable way to detect this lapse in consensus, nor any mechanism to incentivse convergence. Indeed, you have no consensus mechanism in the first place. Bitcoin is where it is today because of Satoshi's elegant solution to exactly such problems. Which some people now appear to be in a hurry to discard :) Alex Mizrahi wrote: > Using scheduled updates: client simply stops working at a certain block, > and user is required to download an update. <snip> > An alternative to this is to make updates mandatory. You will no longer > need to maintain compatibility with version 0.1 (which is impossible) > and you can also evolve consensus rules over time. Peter Todd might disagree with the wisdom of that :) He wrote an excellent email to this list not long ago warning of the dangers of centralisation. IIRC one point he made was that scheduled, regular hardforks were a real threat - if a single entity (eg. the Bitcoin Foundation) were to become politically established as the coordinator of such forks, they would have de-facto control over the protocol. Even in that dark scenario, I would feel a measure of confidence that past transactions I had received could not be tampered with. The fact that those transactions happened, and that there was (and is) consensus they were valid, is publicly documented in the blockchain. I trust any reasonable person would not accept a client that ignored validated data in the blockchain as "Bitcoin" any more. Your proof-of-publication system with mandatory updates is another matter entirely. No public record of transactions I have received with that system exists, anywhere. If tomorrow's mandatory update has the effect of zeroing my account balance (by happening to now interpret one or more transactions I received, or their inputs, as invalid) then I have no recourse. I won't find sympathy with the majority of users, who are unaffected and just accept the update. In short, what you describe doesn't sound very decentralised :) Do you want transactions you receive validated by distributed consensus and burried under PoW, or validated by some guy's mandatory-updating python script? (Also worth noting: all such systems are effectively "mandatory updating" due to the risk of subtle consensus bugs of the type I described above. Your only assurance that your view of the world is the same as everyone elses' is that you're running the exact same software. I played with Counterparty a while ago and quickly learned - the hard way - to do a 'git pull' before any important operation.)
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