Andrew Chow [ARCHIVE] on Nostr: 📅 Original date posted:2023-07-06 🗒️ Summary of this message: The text ...

📅 Original date posted:2023-07-06
🗒️ Summary of this message: The text discusses the potential risks of accepting unconfirmed inputs in a coinjoin and highlights the limitations of package relay. It also mentions that package relay and upcoming package RBF proposals could improve coinjoins.
📝 Original message:
On 07/06/2023 12:22 PM, alicexbt via bitcoin-dev wrote:
> 1) Register input in A
> 2) Double spend same input with zero fee to your own address
> 3) Register unconfirmed UTXO from 2 in B

Why would unconfirmed inputs be accepted in a coinjoin? That seems
unsafe, regardless of package relay. The sender of the unconfirmed
transaction can already replace it thereby pinning or otherwise
invalidating the coinjoin, it doesn't need package relay.

Furthermore, the coordinator B shouldn't accept the unconfirmed UTXO
from 2 because it doesn't even know about that unconfirmed transaction.
It has zero fee, so it's not going to be relayed.

Conceivably a similar attack can already be done by simply registering
the same UTXO with multiple coordinators anyways. This doesn't require
package relay either.

***

Package relay should help coinjoins since any one of the participants
can rebroadcast the coinjoin with a further CPFP if the coinjoin is
below the minimum relay fee. Some of the upcoming package RBF proposals
should also help by allowing other child transactions in the package to
RBF the entire thing, thereby resolving the need to have everyone
re-sign the coinjoin in order to RBF.


Andrew