Re: [Lightning-dev] Commitment Transaction Format Update Proposals?

[Jim Posen]

Instead of leaving an extra output for CPFP, is it not sufficient to just
sign all inputs with ANYONECANPAY and expect the sender to make an exact
output for the fees input? It would require an extra tx assuming they don't
already have a properly sized UTXO handy (which they may!), but I believe
CPFP would require that as well. Am I missing something?

I'm a fan of the symmetric delays because it simplifies the game theory
analysis, but I don't think the delays need to be the same for both
participants (max of `to_self_delay` for both sides), just that the delay
is applied equally regardless of who publishes the commitment tx. Like your
`to_self_delay` can be what I specify and vice versa, what's the reason for
taking the max?

-jimpo
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Re: [Lightning-dev] Commitment Transaction Format Update Proposals?

[Conner Fromknecht]

Good morning everyone,

> We could also use SIGHASH_ANYONECANPAY|SIGHASH_SINGLE
> for HTLC txs, without adding the "OP_TRUE"
> output to the commitment transaction

Doesn’t this require a non-zero number of HTLCs on the commitment txn? We
would still require the OP_TRUE if there are no HTLCs, right?

>From my recollection, HTLC txns with an absolute timeout won’t be accepted
in the mempool until the expiry has matured. So the commitment would have
to be held until that time before it’s descendants can bump the fee rate I
think.

I agree that we should probably modify the HTLC sighashes regardless,
though I wonder if it is a standalone replacement for OP_TRUE.

> 3. The CLTV timeout should be symmetrical to avoid
> trying to game the peer into closing. (Connor IIRC?).

I believe Jimpo proposed this :)

Best,
Conner

On Fri, Oct 19, 2018 at 03:43 Rusty Russell  wrote:

> Fabrice Drouin  writes:
> > Hello,
> >
> >> 1.  Rather than trying to agree on what fees will be in the future, we
> >  > should use an OP_TRUE-style output to allow CPFP (Roasbeef)
> >
> > We could also use SIGHASH_ANYONECANPAY|SIGHASH_SINGLE for HTLC txs,
> without
> > adding the "OP_TRUE" output to the commitment transaction. We would still
> > need the update_fee message to manage onchain fees for the commit tx (but
> > not the HTLC txs) but there would be no reason anymore to refuse fee
> rates
> > that are too high and channels would not get closed anymore when there's
> a
> > spike in onchain fees.
>
> Agreed, that was in the details below:
>
> - HTLC-timeout and HTLC-success txs sigs are
>   SIGHASH_ANYONECANPAY|SIGHASH_SINGLE, so you can Bring Your Own Fees.
>
> The only problem with these proposals is that it requires you have an
> available UTXO to make the CPFP etc.
>
> Cheers,
> Rusty.
>
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