From: "Luke-Jr" <luke@dashjr.org>
To: bitcoin-development@lists.sourceforge.net
Date: Tue, 13 Sep 2011 12:48:29 -0400
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Subject: Re: [Bitcoin-development] Difficulty adjustment / time issues
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On Tuesday, September 13, 2011 11:06:37 AM Gavin Andresen wrote:
> Fixing (2) is easier; incorporating a ntp library and/or simply
> removing the bitcoin mining code from the client but requiring pools
> and miners to have accurate-to-within-a-minute system clocks (or their
> blocks will be "discouraged") seems reasonable to me. If you want to
> produce blocks that the rest of the network will accept, run ntp on
> your system.

This is not currently reasonable. Rolling extranonce is not efficient, and 
using it to generate work for 400+ GH/s worth of miners every new block 
(longpoll) can easily take seconds. Noncerange helps a little, but has poor 
support presently, and still requires an otherwise-unique work per 4 GH/s.
That only leaves pools with the time header to play with. Furthermore, within-
a-minute accuracy basically forces all miners to rollntime-- I'm not against 
this result, but it does mean many miners and pools will be left out in the 
cold.

> I THINK that fixing (2) will make (1) a non-issue-- if miners can't
> mess around with block times very much then it will be very difficult
> for them to manipulate the difficulty for their benefit.

Miners already have very limited area to mess around with block times.
My understanding of these attacks is that they somehow bypass the limitations 
in place.