rich1.0Anthony Towns [ARCHIVE] (npub17r…x9l2h)https://yabu.me/npub17rld56k4365lfphyd8u8kwuejey5xcazdxptserx03wc4jc9g24stx9l2hnjumphttps://yabu.me📅 Original date posted:2020-02-20 📝 Original message: On Tue, Feb 18, 2020 at 10:23:29AM +0100, Joost Jager wrote: > A different way of mitigating this is to reverse the direction in which the > bond is paid. So instead of paying to offer an htlc, nodes need to pay to > receive an htlc. This sounds counterintuitive, but for the described jamming > attack there is also an attacker node at the end of the route. The attacker > still pays. I think this makes a lot of sense. I think the way it would end up working is that the further the route extends, the greater the payments are, so: A -> B : B sends A 1msat per minute A -> B -> C : C sends B 2msat per minute, B forwards 1msat/min to A A -> B -> C -> D : D sends C 3 msat, etc A -> B -> C -> D -> E : E sends D 4 msat, etc so each node is receiving +1 msat/minute, except for the last one, who's paying n msat/minute, where n is the number of hops to have gotten up to the last one. There's the obvious privacy issue there, with fairly obvious ways to fudge around it, I think. But that's rational, because that last node can either (a) collect the payment, covering their cost; or (b) forward the payment, at which point they'll start collecting funds rather than paying them; or (c) cancel the payment releasing all the locked up funds all the way back. I think it might make sense for the payments to have a grace period -- ie, "if you keep this payment open longer than 20 seconds, you have to start paying me x msat/minute, but if it fulfills or cancels before then, it's all good". I'm not sure if there needs to be any enforcement for this beyond "this peer isn't obeying the protocol, so I'm going to close the channel"; not even sure it's something that needs to be negotiated as part of payment routing -- it could just be something each peer does for HTLCs on their channels? If that can be made to work, it doesn't need much crypto or bitcoin consensus changes, or even much deployment coordination, all of which would be awesome. I think at $10k/BTC then 1msat is about the fair price for locking up $5 worth of BTC (so 50k sat) for 1 minute at a 1% pa interest rate, fwiw. Maybe this opens up some sort of an attack where a peer lies about the time to make the "per minute" go faster, but if msats-per-minute is the units, not sure that really matters. Maybe this also implies a different protocol for HTLC forwarding, something like: 1. A sends the HTLC onion packet to B 2. B decrypts it, makes sure it makes sense 3. B sends a half-signed updated channel state back to A 4. A accepts it, and forwards the other half-signed channel update to B so that at any point before (4) Alice can say "this is taking too long, I'll start losing money" and safely abort the HTLC she was forwarding to Bob to avoid paying fees; while only after (4) can she start the time on expecting Bob to start paying fees that she'll forward back. That means 1.5 round-trips before Bob can really forward the HTLC on to Carol; but maybe it's parallelisable, so Bob/Carol could start at (1) as soon as Alice/Bob has finished (2). Cheers aj