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From: Stefan Thomas <moon@justmoon.de>
To: bitcoin-development@lists.sourceforge.net
Subject: Re: [Bitcoin-development] Double spend detection to speed up transaction trust
Date: Fri, 05 Aug 2011 00:10:59 +0200	[thread overview]
Message-ID: <4E3B18F3.4010605@justmoon.de> (raw)
In-Reply-To: <1312490305.3109.46.camel@Desktop666>

Since nobody else has mentioned it: There is another (more pragmatic?) 
way to detect double spends:

1. Connect to lots of clients
2a. If they all send you the same transaction -> double spend unlikely
2b. If some don't send you the transaction (or send a conflicting one) 
-> double spend in progress

Obviously not everyone will run a double spend detector - it's much more 
easily realized as a service (just like mining.) Jan put up a proof of 
concept: http://www.transactionradar.com/

Would network support like a MSG_DOUBLESPEND be better? I used to think 
yes, but looking at the reality of Transaction Radar, I'm not so sure. 
Nothing stops such a service from scaling up and connecting to thousands 
of random nodes (especially when the network itself grows bigger), 
pushing the probabilities of missing a double spend "in the wild" to 
near zero. It could also connect directly to important miners/pools as 
others have suggested.

Of course this doesn't help against double spends where the attacker 
does his own mining*, but neither would MSG_DOUBLESPEND. Given the added 
network load I'd argue that network support for double spends is 
unnecessary and potentially damaging. DoS is more scary to me than 
non-instant transactions.

* In this case of course the hacker will be exposed to some randomness, 
and I doubt many attackers will buy 100 televisions, newspaper 
subscriptions or MP3s to get one for free. So this is only a problem for 
liquid goods with tiny spreads (any investment or stored value instrument.)




  reply	other threads:[~2011-08-04 22:11 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-08-04 13:23 [Bitcoin-development] Double spend detection to speed up transaction trust Andy Parkins
2011-08-04 17:45 ` Matt Corallo
2011-08-04 18:22   ` Andy Parkins
2011-08-04 18:39     ` Matt Corallo
2011-08-04 19:42       ` Andy Parkins
2011-08-04 20:07         ` Andrew Schaaf
2011-08-04 20:38           ` Matt Corallo
2011-08-04 22:10             ` Stefan Thomas [this message]
2011-08-04 22:18               ` Gregory Maxwell
2011-08-04 22:21                 ` Matt Corallo
2011-08-05  0:07                   ` Gavin Andresen
2011-08-04 20:08         ` Gregory Maxwell
2011-08-04 20:33         ` Matt Corallo
2011-08-04 21:36         ` Mike Hearn
2011-08-04 22:16           ` Matt Corallo
2011-08-05  0:14             ` Stefan Thomas
2011-08-05 11:05               ` Mike Hearn
2011-08-05 11:58                 ` Andy Parkins
2011-08-05 12:06                   ` Matt Corallo
2011-08-05 13:03                     ` Andy Parkins
2011-08-05 21:23                       ` Gregory Maxwell
2011-08-05 21:30                       ` Matt Corallo
2011-08-05 12:00               ` Matt Corallo

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