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Date: Mon, 09 Feb 2015 05:37:39 -0800
From: Tom Harding <tomh@thinlink.com>
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To: Peter Todd <pete@petertodd.org>, 
	Bitcoin Dev <bitcoin-development@lists.sourceforge.net>
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Subject: Re: [Bitcoin-development] Update to Double-Spend Deprecation Window
 Proposal
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Many thanks for the feedback Peter.  Please if you would, see below

On 2/8/2015 10:32 PM, Peter Todd wrote:
> Seeing a transaction is not a guarantee that any other node has seen it; not seeing a transaction is not a guarantee other nodes have not seen a spend.

In no way does proposal rely on such assumptions.  It develops local 
rules which result in a desirable outcome for the network as a whole, 
under the applicable statistics.


> you're measuring a network that isn't under attack; Bitcoin must be robust against attacks, and it must not create incentives to launch them.

Two specific attacks are addressed at some length.  No one is keener 
than I to learn of new ones, or flaws in those treatments.


> Institutionalising the punishment of miners being they did not have perfect connectivity - an unattainable goal in a trust less, decentralised system - is athema to the goals of having a decentralised systmem and will only lead to smaller mining operations being punished for being the victim of attacks on their network connectivity that are only made profitable by this proposal.

Building from unavoidable imperfections is the necessary spirit when 
interfacing with physical reality.  I would defer to miners whether 
these specific worries outweigh the benefits of helping to achieve a 30 
second network, rather than a 10±10 minute network.


> Equally your proposal actually makes it *easier* to pull off apparently single-confirm double-spend attacks - any miner who ignores a block containing the apparent double-spend is just as likely to be aiding an attacker trying to get a 1-conf transaction double-spent. This forces *everyone* to waiting *longer* before accepting a transaction because now even a single-confirmation is no longer good evidence of an accepted transaction. In an ecosystem where hardly anyone relies on zeroconf anyway your putting a much larger group of people at risk who weren't at risk before.

I agree on one point -- it is necessary to let transactions mature for 
something on the order of 15 to 30 seconds before mining them, as 
discussed in proposal.  I quite disagree regarding Finney (1-conf) 
attacks.  In fact this proposal is the only one I've seen that actually 
stops most Finney attacks -- all those where the block comes more than 
30 seconds after tx1.