Subject: Re: [bitcoin-dev] [Opt-in full-RBF] Zero-conf apps in immediate danger

From: "David A. Harding" <[email-masked]>
Date: Thu, 20 Oct 2022 11:05:36 -1000

On 2022-10-20 09:58, Anthony Towns via bitcoin-dev wrote:
> On Thu, Oct 20, 2022 at 02:37:53PM +0200, Sergej Kotliar via 
> bitcoin-dev wrote:
>> AJ previously wrote:
>> > presumably that makes your bitcoin
>> > payments break down as something like:
>> >    5% txs are on-chain and seem shady and are excluded from zeroconf
>> >   15% txs are lightning
>> >   20% txs are on-chain but signal rbf and are excluded from zeroconf
>> >   60% txs are on-chain and seem fine for zeroconf
>> Numbers are right. [...]
> 
> [...]
> 
> So the above suggests 25% of payments already get a sub-par experience 
> [...]
> going full rbf would bump that from 25% to 85%, which would be pretty
> terrible.

Is it worth considering incremental steps between opt-in only (BIP125) 
and replace anything full RBF?  For example, in addition to opt-in RBF 
rules, treat any transaction with a txid ending in `0x1` as replacable?  
I assume 1/16th (6.25%) of transactions would match that pattern (some 
of which already opt-in to RBF, so the net effect would be smaller).  
This would have the following advantages:

1. We could see if miners are willing to enable unsignaled RBF at all

2. We could gather more evidence on how the change affects zeroconf 
businesses and everyday users, hopefully without requiring they make 
immediate and huge changes

3. Any wallet authors that oppose unsignaled RBF can opt-out by grinding 
their txids, at least until full RBF is accomplished

4. We can increase the percentage of transactions subject to unsignaled 
RBF in later releases of Bitcoin Core, steadily moving the system 
towards full RBF without any sudden leaps (assuming nobody builds a 
successful relay and mining network with less restrictive replacement 
rules)

I don't think this directly helps solve the problems with non-replacable 
transactions suffered by contract protocols since any adversary can 
opt-out of this scheme by grinding their txid, but I do think there's an 
advantage in transitioning slowly when people are still depending on 
previous behaviors.

Thanks,

-Dave