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Date: Sat, 19 Dec 2015 23:24:52 -0500
From: jl2012 <jl2012@xbt.hk>
To: Chris Priest <cp368202@ohiou.edu>
In-Reply-To: <CAAcC9ys_t7X0WpQ8W3577M8GLiA5sPV2F1BJ9qZbnMkE-1j3+Q@mail.gmail.com>
References: <20151219184240.GB12893@muck>
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	<219f125cee6ca68fd27016642e38fdf1@xbt.hk>
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Message-ID: <aff8da46a69bdd7ef92ca87725866a5c@xbt.hk>
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Cc: bitcoin-dev@lists.linuxfoundation.org, nbvfour@gmail.com
Subject: Re: [bitcoin-dev] We need to fix the block withholding attack
Precedence: list

Chris Priest 於 2015-12-19 22:47 寫到:
> On 12/19/15, jl2012 <jl2012@xbt.hk> wrote:
>> Chris Priest via bitcoin-dev 於 2015-12-19 22:34 寫到:
>>> Block witholding attacks are only possible if you have a majority of
>>> hashpower. If you only have 20% hashpower, you can't do this attack.
>>> Currently, this attack is only a theoretical attack, as the ones with
>>> all the hashpower today are not engaging in this behavior. Even if
>>> someone who had a lot of hashpower decided to pull off this attack,
>>> they wouldn't be able to disrupt much. Once that time comes, then I
>>> think this problem should be solved, until then it should be a low
>>> priority. There are more important things to work on in the meantime.
>>> 
>> 
>> This is not true. For a pool with 5% total hash rate, an attacker only
>> needs 0.5% of hash rate to sabotage 10% of their income. It's already
>> enough to kill the pool
>> 
>> 
> 
> This begs the question: If this is such a devastating attack, then why
> hasn't this attack brought down every pool in existence? As far as I'm
> aware, there are many pools in operation despite this possibility.

It did happen: 
https://www.reddit.com/r/Bitcoin/comments/28242v/eligius_falls_victim_to_blocksolution_withholding/

The worst thing is that the proof for such attack is probabilistic, not
deterministic.

A smarter attacker may even pretend to be many small miners, make it
even more difficult or impossible to prove who are attacking.


> Then shouldn't this be something the pool deals with, not the bitcoin 
> protocol?

The only solution is to ask for KYC registration, unless one could 
propose
a cryptographic solution that does not require a consensus fork.