[bitcoin-dev] SPV Mining reveals a problematic incentive issue.

Eric Lombrozo elombrozo at gmail.com
Mon Jul 13 17:33:31 UTC 2015


>
> On Sat, Jul 11, 2015 at 11:24:48AM +0200, Jorge Timón wrote:
> > All miners should validate transactions precisely because of the latest
> > attack you've described. Full miners can gain a lot from this attack to
> > leverage their full validation against spv miners who blindly spend
> energy
> > hashing on top of something that may be worthless crap. SPV mining makes
> no
> > sense, but some miners claim they're doind it for very short periods of
> > time, which shouldn't be as bad as doing it all the time.
> >
> > I think it would be more rational for them to keep mining on top of the
> old
> > block until they've fully validated the new block (which shouldn't take
> so
> > long anyway), even if this slightly increases the orphan rate.
>
> You're missing something really critical about what F2Pool/AntPool were
> (are?) doing: They're finding out about new blocks not by getting block
> headers from just anywhere, but by connecting to other pools' via
> stratum anonymously and determining what block hash they're telling the
> hashers at the pool to work on. (e.g. what prevblockhash is in the block
> header of shares being generated)
>
> If other pools try to fake this information they're immediately and
> directly losing money, because they're telling their own hashers to make
> invalid blocks. This of course has a high chance of being detected, and
> can easily be FUDed into "STOP MINING AT FOO POOL!" reardless of what
> the ivory tower game theory might say. The only hope the pools have is
> to somehow identify which connections correspond to other pools with
> high reliability and target just those connections - good luck on that.
>
>
> Anyway, all this concern about SPV mining is misguided: relying purely
> on SPV w/ low #'s of confirmations just isn't very smart. What SPV can
> do - at least while the inflation subsidy is still high - is give
> reasonable protection against your third-party-run trusted full nodes
> from lying to you, simply because doing so has well-defined costs in
> terms of energy to create fake blocks. Targetting enough people at once
> to make a fake block a worthwhile investment is difficult, particularly
> when you take into account how timing works in the defenders favor - the
> attacker probably only has a small % of hashing power, so they're going
> to wait a long time to find their fake block. Between that and a trusted
> third party-run full node you're probably reasonably safe, for now.
>
> --
> 'peter'[:-1]@petertodd.org
> 0000000000000000086007e31decd6eb80e07f77271ef50c69e1e6342161f4e5
>
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