and how much it costs to double spend BCH?
that's the wrong question. the attack is not one that can be overcome in the cost dimension. the double spend is one of probability. you send two transactions at the same time and hope one reaches a mining mempool. and that miner gets the next block that's the chance. double spend proofs make even trying once expensive (you get caught). which is why it solved the problem effectively because before a attacker would be able to buy stuff until the double spend succeeded. we removed the one sided risk
and to answer the question. the only empirical tests were done on known compromised full nodes Todd did it with RBF. BU did it some months after they released a client that explicitly turned off the first seen feature. the latter was presented by Peter Rizen in the Italy conference.
i think there are 2 valid questions that need a good evidence-based answer: 1. what's the probability of a double spend success? 2. if it does succeed sometimes, how much would it cost? we can, of course, give answers that make sense but if somebody asks if anyone did an actual study to measure both, i can only say i'm not aware of any.
There has been extensive discussion on Double Spends on BCH research. The general conclusion is that doing double spends in not feasible, impractical. Let me fetch some points... Please stand by.
This sums it up from me: -------------------- The problem is scale and incentives. The only way to earn this way is to either: A: Get a large number of people to use it for smaller (<$1000) purchases B: Get few one time huge shots, but this would have to be really huge amounts, like $50000 to be profitable and worth the bother Scenario A is not even doable anonymously. To get enough people to have any chance of success and significant profit, would require advertisements. To do large scale advertisements, you need to be a company. Case closed. Scenario B can be done anonymously, but only for large sums of money, otherwise it doesn’t make any sense on scale.
https://bitcoincashresearch.org/t/chip-2021-08-zces-zero-confirmation-escrows/537/57
Basically my personal conclusion is that while Double Spends are somewhat possible with miner assist, they are not feasible to do in real life because of limitations of real life - like if you scam a shop, there is Jail time already for it, doesn't matter how you paid. If you repeat it many times, you will get caught, even by accident, by the future. Makes some sense for bigger amounts, but for bigger amounts (like $50k or more), nobody will accept 0-zonf. For such transaction it takes time anyway, so you can wait an hour.
For smaller amounts, if you get other people to do it for a cut (scam double spend wallet), you need advertisements, for advertisements you need a company. Large number of people won't use a scammy wallet if you advertise it on Dark Web or some shady website. While theoretically possible, when you get into details, it turns out it is not doable in real life. Which is exactly why nobody has done it so far, despite 0-conf existing for 15 years.
The experiments done by Peter Rizun (in a video link I picked up from the BCR discussion) shows that a broadcast delay between spend attempts of 3 to 5 seconds already reduces the probability of double spend success to practically zero.
Обсуждают сегодня