On Sat, Jun 09, 2018 at 02:21:17PM +0200, Sergio Demian Lerner wrote: > Also it must be noted that an attacker having only 1.3M USD that can > brute-force 72 bits (4 days of hashing on capable ASICs) can perform the > same attack, so the attack is entirely feasible and no person should accept > more than 1M USD using a SPV wallet.
That doesn't make any sense. Against a SPV wallet you don't need that attack; with that kind of budget you can fool it by just creating a fake block at far less cost, along with a sybil attack. Sybils aren't difficult to pull off when you have the budget to be greating fake blocks. > Also the attack can be repeated: once you create the "extension point" > block, you can attack more and more parties without any additional > computation. That's technically incorrect: txouts can only be spent once, so you'll need to do 2^40 work each time you want to repeat the attack to grind the matching part of the prevout again. -- https://petertodd.org 'peter'[:-1]@petertodd.org
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