On Mon, Jan 22, 2024 at 10:52:01PM +0000, Peter Todd via bitcoin-dev wrote:
> An even simpler fix would be to just require that all unconfirmed inputs in a
> replacement come from the *same* replaced transaction. That would make certain
> rare, but economically viable, replacements infeasible. But it would definitely
> fix the issue.

FYI I've implemented this fix, and pure replace-by-fee-rate with a minimum 2x
fee-rate increate, in my Libre Relay fork:

https://github.com/petertodd/bitcoin/tree/libre-relay-v26.0

Similar to my full-RBF peering fork, it uses a new service bit to ensure it's
peering with other Libre Relay nodes to make transaction propagation actually
works.

I wouldn't call this a "public" release at this point. But people are welcome
to review the code and try it out. I have a few mainnet and testnet nodes
running it right now.

I'm *very* interested if anyone else can find any further exploits in the pure
replace-by-fee-rate code. I'm also interested to see if anyone bothers to spend
the money to do the well-known, and expensive, replace-by-fee-rate DoS attacks.

The fun thing about this release, is Libre Relay also removes the restrictions
on OP_Return, which I'm sure will make some people quite angry... So maybe
that'll give someone an incentive to attack it. :D I'm already sufficiently
well connected to get oversized OP_Return's mined. So if you want to do that
too, running a Libre Relay node will work.

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