On Tue, May 12, 2015 at 7:48 PM, Adam Back <adam@cypherspace.org> wrote:

I think its fair to say no one knows how to make a consensus that
works in a decentralised fashion that doesnt weaken the bitcoin
security model without proof-of-work for now.

Yes.

I am presuming Gavin is just saying in the context of not pre-judging
the future that maybe in the far future another innovation might be
found (or alternatively maybe its not mathematically possible).

Yes... or an alternative might be found that weakens the Bitcoin security model by a small enough amount that it either doesn't matter or the weakening is vastly overwhelmed by some other benefit.

I'm influenced by the way the Internet works; packets addressed to 74.125.226.67 reliably get to Google through a very decentralized system that I'll freely admit I don't understand. Yes, a determined attacker can re-route packets, but layers of security on top means re-routing packets isn't enough to pull off profitable attacks.

I think Bitcoin's proof-of-work might evolve in a similar way. Yes, you might be able to 51% attack the POW, but layers of security on top of POW will mean that won't be enough to pull off profitable attacks.

--
Gavin Andresen