[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 <rusty at rustcorp.com.au> wrote:

> Fabrice Drouin <fabrice.drouin at acinq.fr> 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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