Subject: Re: [bitcoin-dev] V3 Transactions are still vulnerable to significant tx pinning griefing attacks

From: Peter Todd <[email-masked]>
Date: Tue, 2 Jan 2024 23:18:11 +0000

On Tue, Jan 02, 2024 at 11:12:05AM +0000, Gloria Zhao wrote:
> Hi Peter,
> 
> > You make a good point that the commitment transaction also needs to be
> included
> > in my calculations. But you are incorrect about the size of them.
> 
> > With taproot and ephemeral anchors, a typical commitment transaction
> would have
> > a single-sig input (musig), two taproot outputs, and an ephemeral anchor
> > output.  Such a transaction is only 162vB, much less than 1000vB.
> 
> Note that these scenarios are much less interesting for commitment
> transactions with no HTLC outputs, so 162 isn't what I would use for the
> minimum.

What scenarios you consider "interesting" is not relevant. You can't pick an
arbitrary minimum based on an interesting scenario. You should pick an actual
relevant minimum.

So with that in mind, let's ask the question: Do we think it's common for
channels to be force closed without HTLCs pending? I believe the answer is
likely to be yes, because channels are only used some of the time.

Can we verify that? Well, I just checked my node, and out of the past 15 force
closes, 12 had no HTLCs outstanding. 2 had one HTLC outstanding, and 1 had 2
HTLCs.

I also checked a big node I'm connected to, fixedfloat. Again, out of the past
15 force closes, 11 had no HTLCs outstanding, with 4 having 1 HTLC
outstanding... but of those only 2 HTLCs were profitable to collect. The other
half cost more money in fees than the HTLC value.

Looks to me like the supermajority of force closes are the most boring type.
And those numbers would be even more tilted in that direction if Lightning
implementations had better economics management.

-- 
https://petertodd.org 'peter'[:-1]@petertodd.org