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From: Marc Bevand <m.bevand@gmail.com>
Date: Wed, 08 Nov 2017 05:04:07 +0000
Message-ID: <CADH-5r3YqvO4rbS5PEc86LB-CGsrMnARUj7Vbfi0opBB_EuMQA@mail.gmail.com>
To: Robert Taylor <roberttaylorgen@gmail.com>, 
	Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
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Subject: Re: [bitcoin-dev] Centralizing mining by force
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What you describe is an example of a majority attack ("51% attack"). No
technical mechanism in Bitcoin prevents this. However in practice, miners
are not incentivized to perform this attack as it would destroy confidence
in Bitcoin, and would ultimately impact their revenues.

-Marc

On Mon, Nov 6, 2017, 22:32 Robert Taylor via bitcoin-dev <
bitcoin-dev@lists.linuxfoundation.org> wrote:

> Forgive me if this has been asked elsewhere before, but I am trying to
> understand a potential failure mode of Bitcoin mining.
>
> A majority of miners can decide which valid blocks extend the chain. But
> what would happen if a majority of miners, in the form of a cartel decided
> to validly orphan any blocks made by miners outside of their group? For
> example, they could soft fork a new rule where the block number is signed
> by set of keys known only to the cartel, and that signature placed in the
> coinbase. Miners outside of the cartel would not be able to extend the
> chain.
>
> It would be immediately obvious but still valid under the consensus rules.
> What are the disincentives for such behavior and what countermeasures could
> be done to stop it and ensure mining remained permissionless? I think this
> is a valid concern because while it may not be feasible for one actor to
> gain a majority of hash alone, it is certainly possible with collusion.
>
> Robert
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev@lists.linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>

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<p dir=3D"ltr">What you describe is an example of a majority attack (&quot;=
51% attack&quot;). No technical mechanism in Bitcoin prevents this. However=
 in practice, miners are not incentivized to perform this attack as it woul=
d destroy confidence in Bitcoin, and would ultimately impact their revenues=
.</p>
<p dir=3D"ltr">-Marc</p>
<br><div class=3D"gmail_quote"><div dir=3D"ltr">On Mon, Nov 6, 2017, 22:32 =
Robert Taylor via bitcoin-dev &lt;<a href=3D"mailto:bitcoin-dev@lists.linux=
foundation.org">bitcoin-dev@lists.linuxfoundation.org</a>&gt; wrote:<br></d=
iv><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left=
:1px #ccc solid;padding-left:1ex"><div dir=3D"ltr">Forgive me if this has b=
een asked elsewhere before, but I am trying to understand a potential failu=
re mode of Bitcoin mining.<div><br>A majority of miners can decide which va=
lid blocks extend the chain. But what would happen if a majority of miners,=
 in the form of a cartel decided to validly orphan any blocks made by miner=
s outside of their group? For example, they could soft fork a new rule wher=
e the block number is signed by set of keys known only to the cartel, and t=
hat signature placed in the coinbase. Miners outside of the cartel would no=
t be able to extend the chain.<br><br>It would be immediately obvious but s=
till valid under the consensus rules. What are the disincentives for such b=
ehavior and what countermeasures could be done to stop it and ensure mining=
 remained permissionless? I think this is a valid concern because while it =
may not be feasible for one actor to gain a majority of hash alone, it is c=
ertainly possible with collusion.</div><div><br></div><div>Robert</div></di=
v>
_______________________________________________<br>
bitcoin-dev mailing list<br>
<a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org" target=3D"_blank">=
bitcoin-dev@lists.linuxfoundation.org</a><br>
<a href=3D"https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev" =
rel=3D"noreferrer" target=3D"_blank">https://lists.linuxfoundation.org/mail=
man/listinfo/bitcoin-dev</a><br>
</blockquote></div>

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