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Date: Fri, 05 Aug 2011 00:10:59 +0200
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Subject: Re: [Bitcoin-development] Double spend detection to speed up
transaction trust
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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.)
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