Peter Todd <p...@petertodd.org> writes: > On Mon, May 21, 2018 at 01:14:06PM +0930, Rusty Russell via bitcoin-dev wrote: >> Jim Posen <jim.po...@gmail.com> writes: >> > I believe OP_CSV with a relative locktime of 0 could be used to enforce RBF >> > on the spending tx? >> >> Marco points out that if the parent is RBF, this child inherits it, so >> we're actually good here. >> >> However, Matt Corallo points out that you can block RBF will a >> large-but-lowball tx, as BIP 125 points out: >> >> will be replaced by a new transaction...: >> >> 3. The replacement transaction pays an absolute fee of at least the sum >> paid by the original transactions. >> >> I understand implementing a single mempool requires these kind of >> up-front decisions on which tx is "better", but I wonder about the >> consequences of dropping this heuristic? Peter? > > We've discussed this before: that rule prevents bandwidth usage DoS attacks on > the mempool; it's not a "heuristic". If you drop it, an attacker can > repeatedly > broadcast and replace a series of transactions to use up tx relay bandwidth > for > significantly lower cost than otherwise. > > Though these days with relatively high minimum fees that may not matter.
AFAICT the optimal DoS is where: 1. Attacker sends a 100,000 vbyte tx @1sat/vbyte. 2. Replaces it with a 108 vbyte tx @2sat/vbyte which spends one of those inputs. 3. Replaces that spent input in the 100k tx and does it again. It takes 3.5 seconds to propagate to 50% of network (probably much worse given 100k txs), so they can only do this about 86 times per block. That means they send 86 * (100000 + 108) = 8609288 vbytes for a cost of 86 * 2 * 108 + 100000 / 2 = 68576 satoshi (assuming 50% chance 100k tx gets mined). That's a 125x cost over just sending 1sat/vbyte txs under optimal conditions, but it doesn't really reach most low-bandwidth nodes anyway. Given that this rule is against miner incentives (assuming mempool is full), and makes things more complex than they need to be, I think there's a strong argument for its removal. Cheers, Rusty.  http://bitcoinstats.com/network/propagation/  Bandwidth overhead for just sending a 108-vbyte tx is about 160 bytes, so our actual bandwidth per satoshi is closer to 60x even under optimal conditions. _______________________________________________ bitcoin-dev mailing list firstname.lastname@example.org https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev