Subject: Re: [bitcoin-dev] Playing with full-rbf peers for fun and L2s security

From: Peter Todd <[email-masked]>
Date: Fri, 8 Jul 2022 10:53:13 -0400

On Tue, Jul 05, 2022 at 08:46:51PM +0000, alicexbt wrote:
> Hi Peter,
> 
> > Note that Wasabi already has a DoS attack vector in that a participant can stop
> > participating after the first phase of the round, with the result that the
> > coinjoin fails. Wasabi mitigates that by punishing participating in future
> > rounds. Double-spends only create additional types of DoS attack that need to
> > be detected and punished as well - they don't create a fundamentally new
> > vulerability.
> 
> I agree some DoS vectors are already mitigated however punishment in this case will be difficult because the transaction is broadcasted after signing and before coinjoin tx broadcast.
> 
> Inputs are already checked multiple times for double spend during coinjoin round: https://github.com/zkSNACKs/WalletWasabi/pull/6460
> 
> If all the inputs in the coinjoin transaction that failed to relay are checked and one or more are found to be spent later, what will be punished and how does this affect the attacker with thousands of UTXOs or normal users?

Point is, the attacker is thousands of UTXOs can also DoS rounds by simply
failing to complete the round. In fact, the double-spend DoS attack requires
more resources, because for a double-spend to be succesful, BTC has to be spent
on fees.

It's just a fact of life that a motivated attacker can DoS attack Wasabi by
spending money. That's a design choice that's serving them well so far.

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