3 ms·

that won't happen if you're a legit user using a regular client, and for the most part even for a nefarious user it would require significant computing resource

that won't happen if you're a legit user using a regular client, and for the most part even for a nefarious user it would require significant computing resources (e.g. you've already mined a block spending those coins but won't release it until you walk out of the store). Just in case he's not making it clear from the description of what actually doing that would involve, mining a block is a big deal. You're talking about winning the lottery in competition with 35 million other gigahash/sec worth of mining power. If the worst you want to do with that block is defraud a mom and pop store that accepts bitcoin you're positing a scenario something on the order of a multimillion dollar operation in order to undertake such an attempt. If you're going to do that, you're not going to try to defraud the corner store for a snickers bar. Also, if that's genuinely not enough; Not to mention there are other crypto-currencies with significantly faster block clearing times, and cryptocoin to cryptocoin exchanges are significantly easier to run than bitcoin to fiat exchanges. Plenty of 60 second block confirm altcoin chains out there, no reason to use bitcoin if you absolutely insist on some way to address the double spend "problem".

jedunnigan 13y ago
So having a miner in your pocket is certainly one way to execute a double spend. That's a Finney attack.[0] The other and less costly way is all about node connectivity.[1] If you are going to execute a double spend all you 'need' to do is broadcast two txs spending the same output at the same time--one going to the merchant the other spending it back to yourself--and cross your fingers and hope the double spend gets put in a block. Now, you can increase the probability (e.g. shielding the merchant's node from your double spend) of success but it's not a sure bet. And the higher the node connectivity of the network (i.e. how many nodes are each node connected to) the harder this attack becomes. There has been some work in this area, especially in pursuit of the efficacy of double spend attacks in light of some minor changes to the protocol which (I think) were rolled into core with the most release 0.9.0.[2] It's about .09% probability of success. [0]https://en.bitcoin.it/wiki/Weaknesses#The_Finney_attack https://en.bitcoin.it/wiki/Weaknesses#The_Finney_attack [1]http://www.tik.ee.ethz.ch/file/49318d3f56c1d525aabf7fda78b23fc0/P2P2013_041.pdf http://www.tik.ee.ethz.ch/file/49318d3f56c1d525aabf7fda78b23... [2]http://www.tik.ee.ethz.ch/file/848064fa2e80f88a57aef43d7d5956c6/P2P2013_093.pdf http://www.tik.ee.ethz.ch/file/848064fa2e80f88a57aef43d7d595...

jedunnigan 13y ago

So having a miner in your pocket is certainly one way to execute a double spend. That's a Finney attack.[0] The other and less costly way is all about node connectivity.[1] If you are going to execute a double spend all you 'need' to do is broadcast two txs spending the same output at the same time--one going to the merchant the other spending it back to yourself--and cross your fingers and hope the double spend gets put in a block. Now, you can increase the probability (e.g. shielding the merchant's node from your double spend) of success but it's not a sure bet. And the higher the node connectivity of the network (i.e. how many nodes are each node connected to) the harder this attack becomes. There has been some work in this area, especially in pursuit of the efficacy of double spend attacks in light of some minor changes to the protocol which (I think) were rolled into core with the most release 0.9.0.[2] It's about .09% probability of success. [0]https://en.bitcoin.it/wiki/Weaknesses#The_Finney_attack https://en.bitcoin.it/wiki/Weaknesses#The_Finney_attack [1]http://www.tik.ee.ethz.ch/file/49318d3f56c1d525aabf7fda78b23fc0/P2P2013_041.pdf http://www.tik.ee.ethz.ch/file/49318d3f56c1d525aabf7fda78b23... [2]http://www.tik.ee.ethz.ch/file/848064fa2e80f88a57aef43d7d5956c6/P2P2013_093.pdf http://www.tik.ee.ethz.ch/file/848064fa2e80f88a57aef43d7d595...