From: Isidor Zeuner <cryptocurrencies@quidecco.de>
To: Paul Goldstein <paul@realfoot.com>
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Message-Id: <20140617155845.8177ADFC55C@quidecco.de>
Date: Tue, 17 Jun 2014 17:58:45 +0200 (CEST)
Cc: Bitcoin Dev <bitcoin-development@lists.sourceforge.net>
Subject: Re: [Bitcoin-development] instant confirmation via payment protocol
 backwards compatible proto buffer extension
Precedence: list

quote:
> Mike Hearn, why don't we just have all nodes report attempted double spends
> through the node network. No need to involve the miners at all really, or
> do your suggestion but also report the double spend attempt. By waiting
> maybe 10-60 seconds (instead of 10 minutes for first conf), merchants can
> be more sure that a double spend attack was not tried. Attacker would have
> to hold back second tx by 10-60 seconds and hope that that second tx (with
> higher fee) get's into a solved block before the first one. This forced
> delay time ought to make the attack less successful (but not impossible).
>

What prevents the following steps from happening:

1. attacker sends first transaction, paying to the merchant

2. merchant waits 10-60 seconds

3. merchant confirms the payment as received

4. attacker sees merchant's confirmation

5. attacker sends double spend

The security improvement seems to be pretty much exactly the chance
that during the 10-60 seconds, a block is solved. Am I missing
something?

Regarding "reporting double spends", this would only help if it comes
with some kind of penalty for the double spend. Now what if the double
spend was not done on malicious motives? Maybe someone posted a
transaction which does not confirm for some reason, and wants to
recover his funds? Should we regard transactions which do not confirm
as forever lost, in order to get to an "every double spend is a
misbehaviour" policy?

Best regards,

Isidor