Jim Posen <jim.po...@gmail.com> writes: > Can you explain why a fixed offset along the whole circuit is enough to > ensure safely as opposed to an increased delta at each hop?
Sure. Let's assume we have chosen a path `A->B->C->D->E`. For simplicity let's assume they all have a CLTV delta of 144 blocks (lnd's default setting). Furthermore let's assume that the CSV timeout for the channels is also 144. This means that with the current LN-penalty mechanism you'd have the following CLTV deltas in the HTLC: ``` A -(576)-> B -(432)-> C -(288)-> D -(144)-> E ``` Meaning that if the current time is approaching the absolute CLTV we need initiate a channel closure to safely fetch the preimage on-chain, and be able to turn around and send it on the upstream channel. This is minimal, but can be arbitrarily higher, if you follow the best practice of obfuscating the final destination by building a shadow route behind the real recipient, and add it's CLTV deltas and fees to your route. With eltoo you'd need to make sure that you have the settlement transaction confirmed before your desired CLTV timeout delta begins to count down. So if the CLTV of the HTLC is `now + CSV timeout + CLTV delta` you need to initiate a close, whereas Lightning allows you to wait for time `now + CLTV delta`. Effectively this results in the following time deltas: ``` A -(576+144)-> B -(432+144)-> C -(288+144)-> D -(144+144)-> E ``` Taking the last hop for example, if we had a CLTV of 1000 with eltoo we'd need to start closing at height 712, instead of 856 with LN-penalty. However, this increased delta does not accumulate along the path, it's just a fixed offset. The longer the route, the smaller the actual impact of this offset. _______________________________________________ bitcoin-dev mailing list firstname.lastname@example.org https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev