Bastien TEINTURIER [ARCHIVE] on Nostr: 📅 Original date posted:2020-10-23 📝 Original message: Thanks for your answers, ...

📅 Original date posted:2020-10-23
📝 Original message:
Thanks for your answers,

My first instinct is that additional complications are worse in general.
> However, it looks like simpler solutions are truly not enough, so adding
> the complication may very well be necessary.


I agree with both these statements ;). I'd love to find a simpler solution,
but this is the simplest
I've been able to come up with for now that seems to work without adding
griefing vectors...

The succeeding text refers to HTLCs "settling".


As you noted, settling means getting the HTLC removed from the commitment
transaction.
It includes both fulfills and fails, otherwise the proposal indeed doesn't
penalize spam.

If we also require that the hold fee be funded from the main output, then
> we cannot use single-funded channels, except perhaps with `push_msat`.


I see what you mean, the first payment cannot require a hold fee since the
fundee doesn't have a
main output. I think it's ok, it's the same thing as the reserve not being
met initially.

But you're right that there are potentially other mechanisms to enforce the
fee (like your suggestion
of subtracting from the HTLC output), I chose the simplest for now but we
can (and will) revisit
that choice if we think that the overall mechanisms work!

And in this case C earns.

Can C delay the refund to D to after the grace period even if D settled the
> HTLC quickly?


Yes C earns, but D has misbehaved. As a final recipient, D isn't dependent
on anyone downstream.
An honest D should settle the HTLC before the `grace_period` ends. If D
chooses to hold the HTLC
for a while, then it's fair that he pays C for this.

it is the fault of the peer for getting disconnected and having a delay in
> reconnecting, possibly forfeiting the hold fee because of that.


I think I agree with that, but we'll need to think about the pros and cons
when we get to details.

Is 1msat going to even deter anyone?

I am wondering though what the values for the fwd and bwd fees should be. I
> agree with ZmnSCPxj that 1 msat for the fwd is probably not going to be
> enough.


These values are only chosen for the simplicity of the example's sake. If
we agree the proposal works
to fight spam, we will do some calculations to figure a good value for
this. But I think finding the
right base values will not be the hard part, so we'll focus on this if
we're convinced the proposal
is worth exploring in full details.

It is interesting that the forward and backward payments are relatively
> independent of each other


To explain this further, I think it's important to highlight that the
forward fee is meant to fight
`uncontrolled spam` (where the recipient is an honest node) while the
backward fee is meant to fight
`controlled spam` (where the recipient also belongs to the attacker).

The reason it works is because the `uncontrolled spam` requires the
attacker to send a large volume
of HTLCs, so a very small forward fee gets magnified. The backward fee will
be much bigger because
in `controlled spam`, the attacker doesn't need a large volume of HTLCs but
holds them for a long
time. What I think is nice is that this proposal has only a tiny cost for
honest senders (the
forward fee).

What I'd really like to explore is whether there is a type of spam that I
missed or griefing attacks
that appear because of the mechanisms I introduce. TBH I think the
implementation details (amounts,
grace periods and their deltas, when to start counting, etc) are things
we'll be able to figure out
collectively later.

Thanks again for your time!
Bastien


Le ven. 23 oct. 2020 à 07:58, Joost Jager <joost.jager at gmail.com> a écrit :

> Hi Bastien,
>
> We add a forward upfront payment of 1 msat (fixed) that is paid
>> unconditionally when offering an HTLC.
>> We add a backwards upfront payment of `hold_fees` that is paid when
>> receiving an HTLC, but refunded
>> if the HTLC is settled before the `hold_grace_period` ends (see footnotes
>> about this).
>>
>
> It is interesting that the forward and backward payments are relatively
> independent of each other. In particular the forward anti-spam payment
> could quite easily be implemented to help protect the network. As you said,
> just transfer that fixed fee for every `update_add_htlc` message from the
> offerer to the receiver.
>
> I am wondering though what the values for the fwd and bwd fees should be.
> I agree with ZmnSCPxj that 1 msat for the fwd is probably not going to be
> enough.
>
> Maybe a way to approach it is this: suppose routing nodes are able to make
> 5% per year on their committed capital. An aggressive routing node could be
> willing to spend up to that amount to take down a competitor.
>
> Suppose the network consists only of 1 BTC, 483 slot channels. What should
> the fwd and bwd fees be so that even an attacked routing node will still
> earn that 5% (not through forwarding fees, but through hold fees) in both
> the controlled and the uncontrolled spam scenario?
>
> - Joost
>
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