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

From: Tier Nolan <[email-masked]>
Date: Sat, 11 Jul 2015 11:39:38 +0100

On Sat, Jul 11, 2015 at 10:24 AM, Jorge Timón <[email-masked]> wrote:

> 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.

Increased orphan rate means that the network is (slightly) less secure.

If miners have a 5% orphan rate, then an attacker can launch a 51% attack
with 49% of the network.

It isn't a massive difference, but it is there.

As long as miners switch back to non-SPV mining after a timeout, SPV-mining
is safe for everyone.

The average cost to the miner from building on an invalid block is small,
as long as invalid blocks only happen rarely.

Miners still have an incentive to do full validation, so that they can
include transactions and get transaction fees.

SPV-mining is to prevent hashing hardware from having to waste power when
it isn't needed.

It may be less of a problem if (when?) electricity costs dominate hardware
capital costs.