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Date: Sat, 11 Jul 2015 11:39:38 +0100
Message-ID: <CAE-z3OWOoHfMaEN04CQ-j8tzmAr1+Evjh+tfHRDbF6F1jxykHA@mail.gmail.com>
From: Tier Nolan <tier.nolan@gmail.com>
Cc: bitcoin-dev@lists.linuxfoundation.org
Content-Type: multipart/alternative; boundary=001a1147732ef7d9af051a971a0d
Subject: Re: [bitcoin-dev] SPV Mining reveals a problematic incentive issue.
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On Sat, Jul 11, 2015 at 10:24 AM, Jorge Tim=C3=B3n <jtimon@jtimon.cc> 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 ta=
ke
> 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.

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<div dir=3D"ltr"><br><div class=3D"gmail_extra"><br><div class=3D"gmail_quo=
te">On Sat, Jul 11, 2015 at 10:24 AM, Jorge Tim=C3=B3n <span dir=3D"ltr">&l=
t;<a href=3D"mailto:jtimon@jtimon.cc" target=3D"_blank">jtimon@jtimon.cc</a=
>&gt;</span> wrote:<br><blockquote class=3D"gmail_quote" style=3D"margin:0 =
0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">I think it would be m=
ore rational for them to keep mining on top of the old block until they&#39=
;ve fully validated the new block (which shouldn&#39;t take so long anyway)=
, even if this slightly increases the orphan rate.
</blockquote><div><br></div><div>Increased orphan rate means that the netwo=
rk is (slightly) less secure.<br></div><div><br></div><div>If miners have a=
 5% orphan rate, then an attacker can launch a 51% attack with 49% of the n=
etwork.<br><br></div><div>It isn&#39;t a massive difference, but it is ther=
e.<br><br></div><div>As long as miners switch back to non-SPV mining after =
a timeout, SPV-mining is safe for everyone.<br><br></div><div>The average c=
ost to the miner from building on an invalid block is small, as long as inv=
alid blocks only happen rarely.<br></div><br></div>Miners still have an inc=
entive to do full validation, so that they can include transactions and get=
 transaction fees.<br><br></div><div class=3D"gmail_extra">SPV-mining is to=
 prevent hashing hardware from having to waste power when it isn&#39;t need=
ed.<br><br></div><div class=3D"gmail_extra">It may be less of a problem if =
(when?) electricity costs dominate hardware capital costs.<br></div></div>

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