This idea was suggested by "Joe" on 2011-02-14 https://bitcointalk.org/index.php?topic=3441.msg48484#msg48484 . It deserves another look.
Nodes today make a judgment regarding which of several conflicting spends to accept, and which is a double-spend. But there is no incorporation of these collective judgments into the blockchain. So today, it's the wild west, right up until the next block. To address this: - Using its own clock, node associates a timestamp with every transaction upon first seeing its tx hash (at inv, in a block, or when created) - Node relays respend attempts (subject to anti-DOS rules, see github PR #3883) - Eventually, node adds a consensus rule: Do not accept blocks containing a transaction tx2 where - tx2 respends an output spent by another locally accepted transaction tx1, and - timestamp(tx2) - timestamp(tx1) > T What is T? According to http://bitcoinstats.com/network/propagation/ recent tx propagation has a median of 1.3 seconds. If double-spender introduces both transactions from the same node, assuming propagation times distributed exponentially with median 1.3 seconds, the above consensus rule with reject threshold T = 7.4 seconds would result in mis-identification of the second-spend by less than 1% of nodes.* If tx1 and tx2 are introduced in mutually time-distant parts of the network, a population of nodes in between would be able to accept either transaction, as they can today. But the attacker still has to introduce them at close to the same time, or the majority of the network will confirm the one introduced earlier. Merchant is watching also, and these dynamics mean he will not have to watch for very long to gain confidence if he was going to get double-spent, he would have learned it by now. The consensus rule also makes mining a never-broadcast double-spend quite difficult, because the network assigns it very late timestamps. Miner has to get lucky and find the block very quickly. In other words, it converges to a Finney attack. This would be the first consensus rule that anticipated less than 100% agreement. But the parameters could be chosen so that it was still extremely conservative. Joe also suggested a fail-safe condition: drop this rule if block has 6 confirmations, to prevent a fork in unusual network circumstances. We can't move toward this, or any, solution without more data. Today, the network is not transparent to double-spend attempts, so we mostly have to guess what the quantitative effects would be. The first step is to share the data broadly by relaying first double-spend attempts as in github PR #3883. *Calcs: For Exp(lambda), median ln(2)/lambda = 1.3 ==> lambda = .533 Laplace(0,1/lambda) < .01 ==> T = 7.34 seconds ------------------------------------------------------------------------------ "Accelerate Dev Cycles with Automated Cross-Browser Testing - For FREE Instantly run your Selenium tests across 300+ browser/OS combos. Get unparalleled scalability from the best Selenium testing platform available. Simple to use. Nothing to install. Get started now for free." http://p.sf.net/sfu/SauceLabs _______________________________________________ Bitcoin-development mailing list Bitcoinfirstname.lastname@example.org https://lists.sourceforge.net/lists/listinfo/bitcoin-development