--- Log opened Sat Jul 29 00:00:13 2023
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09:36 < harding> _aj_: are the upfront commitment fee + reverse hold fees in https://lists.linuxfoundation.org/pipermail/lightning-dev/2023-July/004020.html basically the same as the reverse hold fees in https://lists.linuxfoundation.org/pipermail/lightning-dev/2020-February/002548.html plus the upfront fee mentioned later in the thread at https://lists.linuxfoundation.org/pipermail/lightning-dev/2020-February/002561.html ? 
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10:01 < harding> I think the forward commitment fee needs to be proportional to the transfered amount, otherwise Mallory can cancel just before the reverse hold fee goes into effect to earn money on a transfer that's sufficiently high value.  For example, if the forward commitment fee is 1 msat across all hops and Mallory pays Mallory through 20 intermediaries (incurring a 20 msat fee) but Mallory sends an amount large enough that the reverse hold fee is 21 msat 
10:01 < harding> to her spending node, she can become well connected to miners and have her receiving node cancel the HTLC immediately after she sees a block but before the receiving node's counterparty sees the block, leaving that counterparty (not Mallory) on the hook for a fee.  The fee propagates backwards until Mallory's sending node receives more reverse hold fee than it spent on forward commitment fees.  If the forward fee is equal to or greater than, say, 
10:01 < harding> three blocks of reverse hold fees (or however many blocks we believe is the maximum Mallory could ever learn about before the rest of the network learns about them), then she shouldn't be able to profit.  (Note, what I've described obviously arises from the concerns stated by rusty in the 2020 thread.)
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10:22 < harding> For a $1,000 payment and 10 ppa to each of 20 hops, that implies a minimum upfront commitment fee of about 0.11.  If you redundantly overpay or have many paths fail, I'd guess that could reasonably go up to about $0.50, or about the same as the 0.05% success fees you recent post says Phoenix requires as a minimum.
10:23 < harding> 1000 * 0.1 * (30 / 60 / 24 / 365) * 20
10:38 < harding> Having thought about this for a bit, I think rusty's criticism about time on the 2020 thread and the comments in the meeting notes about not having a universal time source are a compelling argument against what is otherwise one of my favorite schemes (because it both prevents jamming and also adds an economic function to invoice holding).  Even the block chain doesn't seem to provide a universal clock here, as I understand the proposal, given that
10:38 < harding>  different nodes will receive new blocks at different times.  If the scheme is implemented (as I understand it), there will naturally be times when HTLCs are being cancelled or settled simultaneously with blocks propagating across the network and the reverse hold fees from a downstream hop (closer to the receiver/canceller) will see fewer ticks of the block than upstream hops, potentially leading to someone who is not responsible for delaying the 
10:38 < harding> HTLC having to pay more reverse commitment fees than they received.  Higher upfront commitment fees can compensate for that, but only AFAICT by making payments significantly more expensive.
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23:02 < _aj_> harding: haha, you found the thread that "an email about this sitting in my drafts for a few years now" was referring to
23:17 < _aj_> in my recent email, the "upfront commitment fee" is just paying for bandwidth, so is extremely trivial for payments, and can be treated as 0 here i think. so the attack is just setup a route "M1 -> A -> M2" with M1 claiming a large hold fee, and M2 holding on to the HTLC long enough to trigger A to pay M1, but not long enough for M2 to pay A. I think it's probably solvable. you could probably just 
23:17 < _aj_> count down the blocks, even? A->B->C->D -- B pays A every block if the HTLC is still open at block 20, C pays B every block if it's still open after block 17, D pays C if it's still open after block 15?
23:21 < _aj_> we're talking 12msat per hop per block for a $20 payment at 10% pa interest or 1msat per hop per block at 1% pa interest; feels like there's a lot of scope to just ignore small errors
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--- Log closed Sun Jul 30 00:00:14 2023