[Lightning-dev] Proposal for Advertising Channel Liquidity

Jim Posen jim.posen at gmail.com
Thu Nov 8 02:40:13 UTC 2018

Thanks for proposing this! I think it is absolutely one of the biggest
onboarding/usability challenges for many use cases.

My first thought is that like ZmnSCPxj mentioned, the person offering
liquidity can simply close the channel. So if I'm charging for liquidity,
I'd actually want to charge for the amount (in mSAT/BTC) times time. So
like 1 mSAT per satoshi of bandwidth per hour or something like that. I
don't think there's a perfect way of enforcing this at the protocol layer,
but maybe you could lock up the fees in channel reserve which decreases
over time and gets donated to miners on an early close?

Instead of a flat payment for liquidity, I've considered in the past a
model where you pre-pay on fees. So if I'm a large merchant and I expect to
be receiving lots of volume in payments, it is totally rational for you to
put up liquidity opening a channel to me because you will earn fees on
payments routed to me through that channel. So what I could do to convince
you is to say, "I expect if you open a 1 BTC channel to me, you will earn
at least 10 mSAT per minute in routing fees. And if you don't I'll cover
the difference." So every minute, I'll pay you 10 mSAT up front, then for
all HTLCs that come through the channel to me up to that limit, you'll
forward the fees onto me as reimbursement. I don't think this protocol is
any less vulnerable to attacks, but perhaps aligns incentives better?

My other concern with this sort of proposal is that it makes it easier to
perform HTLC withholding/loop attacks, which are executed by the receiving
end of a circuit. Currently on the network, there's a nice built-in
protection that it's not obvious how to convince victim to open a channel
to you. This is probably something that should get dealt with separately,
but part of me doubts that it'll be possible to create a liquidity market
without factoring in reputation.
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