[Cryptography] Electronic currency revived after 20-year hiatus

[Peter Todd]

On Thu, Aug 18, 2016 at 02:15:00PM -0400, Allen wrote:
> >
> > Note that Bitcoin - specifically proof-of-work - does solve a problem that
> > signature-based approaches can't: even if the people building consensus in
> > Bitcoin (miners) all conspire to change history, it's provably expensive
> > for
> > them to rewrite history because they have to re-do all the proof-of-work.
> > That's not true in signature based consensus, as forging a signature is
> > free.
> >
> 
> Not so easy though if all honest participants use a signing key only once,
> publishing a new public signing key and overwriting the old private key
> each time they sign a block.  Once the old private key is overwritten, it's
> impossible to revise the history (except to rewrite it completely by
> changing the software to accept a different genesis block, which I think
> would be possible with any blockchain).

That's the thing with proof-of-work: you get that guarantee even if miners
aren't honest. Even dishonest miners have to re-do work, with provable
expendetures, to re-write history. All you need to assume is that miners are
economically rational actors, which is a stronger threat model than needing
honest participants.

Additionally, because consensus systems can be layered, once one proof-of-work
system exists other consensus systems can piggyback on it for additional
security. For instance, a signature-based consensus system can additionally
require that the system state be published on a PoW blockchain periodically,
with the protocol defining a state as valid only if that publication exists
(perhaps with some time-window for cost/latency reduction of recent history).
By doing that attacks have a much higher chance of being detected, because the
PoW consensus forces the attacker to publish the fact that the attack is
happening widely.

-- 
https://petertodd.org 'peter'[:-1]@petertodd.org
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