On 28 January 2017 02:36:16 GMT-08:00, Natanael via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote: >Den 28 jan. 2017 05:04 skrev "Luke Dashjr via bitcoin-dev" < >bitcoin-dev@lists.linuxfoundation.org>: > >Satoshi envisioned a system where full nodes could publish proofs of >invalid >blocks that would be automatically verified by SPV nodes and used to >ensure >even they maintained the equivalent of full node security so long as >they >were >not isolated. But as a matter of fact, this vision has proven >impossible, >and >there is to date no viable theory on how it might be fixed. As a >result, the >only way for nodes to have full-node-security is to actually be a true >full >node, and therefore the plan of only having full nodes in datacenters >is >simply not realistic without transforming Bitcoin into a centralised >system. > > >Beside Zero-knowledge proofs, which is capable of proving much so more >than >just validity, there are multi types of fraud proofs that only rely on >the >format of the blocks. Such as publishing the block header + the two >colliding transactions included in it (in the case of double spending), >or >if the syntax or logic is broken then you just publish that single >transaction.
That's a perfect example of why fraud proofs aren't as secure as expected: the miner who created such a block wouldn't even give you the data necessary to prove the fraud in the first place. What you actually need are validity challenges, where someone makes a challenge claiming that part of the block is invalid. A failure to meet the challenge with proof that the rules are followed is considered defacto evidence of fraud. But validity challenges don't scale well and pose DoS attacks issues; it's far from clear that they can be implemented in a useful way. Even if validity challenges work, they also don't solve censorship: a world of nodes in large datacenters is a world where it's very easy to force the few Bitcoin nodes remaining to follow AML/KYC rules for instance, a risk we wouldn't be able to mitigate with a PoW change.
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