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Date: Tue, 5 Nov 2013 12:05:41 -0500
From: Peter Todd <pete@petertodd.org>
To: Ittay <ittay.eyal@cornell.edu>
Message-ID: <20131105170541.GA13660@petertodd.org>
References: <CABT1wWkOukEzxK5fLbnA4ZgJGN1hb_DMteCJOfA13FE_QZCi=Q@mail.gmail.com>
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Cc: Bitcoin Dev <bitcoin-development@lists.sourceforge.net>,
	Gavin Andresen <gavin@bitcoinfoundation.org>,
	Emin =?iso-8859-1?B?R/xu?= Sirer <egs@systems.cs.cornell.edu>
Subject: Re: [Bitcoin-development] BIP proposal - patch to raise selfish
 mining threshold.
Precedence: list


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On Tue, Nov 05, 2013 at 11:56:53AM -0500, Ittay wrote:
> Hello,
>=20
> Please see below our BIP for raising the selfish mining threshold.
> Looking forward to your comments.

<snip>

> 2. No new vulnerabilities introduced:
> Currently the choice among equal-length chains is done arbitrarily,
> depending on network topology. This arbitrariness is a source of
> vulnerability. We replace it with explicit randomness, which is at the
> control of the protocol. The change does not introduce executions that we=
re
> not possible with the old protocol.

Credit goes to Gregory Maxwell for pointing this out, but the random
choice solution does in fact introduce a vulnerability in that it
creates incentives for pools over a certain size to withhold blocks
rather than immediately broadcasting all blocks found.

The problem is that when the pool eventually choses to reveal the block
they mined, 50% of the hashing power switches, thus splitting the
network. Like the original attack this can be to their benefit. For
pools over a certain size this strategy is profitable even without
investing in a low-latency network; Maxwell or someone else can chime in
with the details for deriving that threshold.

I won't get a chance to for a few hours, but someone should do the
analysis on a deterministic switching scheme.

--=20
'peter'[:-1]@petertodd.org
0000000000000005e25ca9b9fe62bdd6e8a2b4527ad61753dd2113c268bec707

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