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authorAndy Parkins <andyparkins@gmail.com>2011-08-04 19:22:16 +0100
committerbitcoindev <bitcoindev@gnusha.org>2011-08-04 18:22:29 +0000
commit3149dc52cf1c7497ee4869e2572797b551aff517 (patch)
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parent1d11ce13d18c69578bcf9b6e1ac2ef37a2248553 (diff)
downloadpi-bitcoindev-3149dc52cf1c7497ee4869e2572797b551aff517.tar.gz
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Re: [Bitcoin-development] Double spend detection to speed up transaction trust
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+From: Andy Parkins <andyparkins@gmail.com>
+To: bitcoin-development@lists.sourceforge.net
+Date: Thu, 4 Aug 2011 19:22:16 +0100
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+Subject: Re: [Bitcoin-development] Double spend detection to speed up
+ transaction trust
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+
+On Thursday 04 August 2011 18:45:17 Matt Corallo wrote:
+> There really is no reason to add the extra network complexity for this.
+
+It's hardly complex. It's exactly as it is now, with exactly the messages
+there are now, but with an extra type added to the inventory list. A
+transaction _already_ propagates using inv messages with MSG_TX, is it
+really so "complex" to add MSG_DOUBLESPEND to the enum? What's more it's
+backward compatible because clients that don't understand MSG_DOUBLESPEND
+will ignore the inv ending up exactly where we are now.
+
+> First of all (as you point out) no one buying a Ferrari will refuse to
+> wait an hour for the payment to confirm. If someone is attempting to
+> pull a similar trick on, say, a vending machine however it might make
+> sense. But that changes the equation. In order for these two scammers
+
+Vending machine, newspaper salesman, ice creams, a beer. The list of small
+vendors is endless. I picked Ferrari's out of the air.
+
+> to pull it off, some effort is required in terms of communicating the
+> time to send the coins and the nodes of the targets (vending machines or
+> whatever) must be figured out. So now its less of "make it impossible"
+> and more of "make it really hard to the point that it is no where near
+> worth the effort".
+
+I think you've missed the point. Double spend transactions that enters the
+network at two reasonably evenly connected points are each only seen by half
+the network, since the first one locks out the second from propagation.
+
+> Lets simplify the scenario a bit so that one scammer can pull it off.
+> Send one copy of your transaction to the target node and another to
+> large mining operations so that the payment transaction is considered
+> invalid to miners and a transaction which pays you is confirmed.
+
+There is no "target" node. There is only a vending machine listening for
+transactions. It's unlikely that vending machines will even have incoming
+connections enabled. They certainly won't be keeping a full copy of the
+block chain or be mining.
+
+> If you are the vending machine, your goal is not to figure out any
+> transactions which are yours, but to figure out which transactions which
+
+It is a little bit. Your job is _first_ to figure out which are yours;
+then, as you say, to see which are going to be confirmed. Well: once you've
+seen a transaction on the net you know it's going to be confirmed... unless
+a matching double spend transaction was accepted by the next miner to
+generate a block.
+
+> are yours are going to be confirmed. So, you peer with the largest
+> miners (a "Bitcoin backbone" or large miners and merchants has been
+> suggested over and over again and really hasn't happened) and modify
+
+It hasn't happened, and yet it seems to be that this non-existant thing is
+your solution to the problem.
+
+> your client to, instead of dropping transactions which are
+> double-spends, keep both in memory pool and consider them both invalid
+> until one of them confirms.
+
+Well that's what happens now. But that doesn't help the poor sap who's just
+handed over some goods. I want it so that small businesses can use the
+client to give them practical answers instead of this "0/unconfirmed" stuff
+which requires understanding of the system.
+
+> This will work with 1, 2, or n scammers, doesn't require any additional
+> network messages, and offers just as good, if not better security over a
+> double spend message.
+
+I'm not really trying to prevent double spends -- bitcoin _already_ prevents
+double spends. Also: the only difference between your suggestion (don't
+drop) and my suggestion (don't drop but mark with MSG_DOUBLESPEND) is a
+single number in the inv. I really don't get the objection.
+
+> Additionally, in the future, when(/if) Bitcoin payment processors exist,
+
+"In the future" is all well and good. What if there is no future because
+bitcoin is still too difficult for average joe to use?
+
+
+
+Andy
+
+--
+Dr Andy Parkins
+andyparkins@gmail.com
+
+