Date: Fri, 08 Jul 2022 19:44:24 +0000
To: Peter Todd <pete@petertodd.org>
From: alicexbt <alicexbt@protonmail.com>
Reply-To: alicexbt <alicexbt@protonmail.com>
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Cc: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Playing with full-rbf peers for fun and L2s
	security
Precedence: list

Hi Peter,

> Point is, the attacker is thousands of UTXOs can also DoS rounds by simpl=
y
> failing to complete the round. In fact, the double-spend DoS attack requi=
res
> 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.


There are 2 things:

1) Based on my understanding, round will not be aborted if a threshold is m=
et for inputs and will continue irrespective of attacker trying different t=
hings in the initial phases of round. I need to confirm this by testing alt=
hough not feeling well today so it can take a few days.

2) Points mentioned by Greg Sanders are reasonable: There can be a differen=
t 'mempool view' for coordinator, users and attacker. Attacker could use mi=
nimum fee rate required for relay and this works differently when there is =
enough demand for blockspace.

Double spend attack requires only one laptop and a few UTXOs. Even if spent=
 in some cases, would pay a few sats per transaction which won't be an issu=
e for governments or competitors that normally perform such attacks.

The vulnerability reported is different from the things being discussed and=
 hopefully I will do a public disclosure this month. I observed some intere=
sting things which I wanted to discuss. Full RBF pull request is already me=
rged in bitcoin core and available in bitcoin knots if some users want to e=
xperiment.


/dev/fd0

Sent with Proton Mail secure email.

------- Original Message -------
On Friday, July 8th, 2022 at 2:53 PM, Peter Todd <pete@petertodd.org> wrote=
:


> 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 participan=
t can stop
> > > participating after the first phase of the round, with the result tha=
t the
> > > coinjoin fails. Wasabi mitigates that by punishing participating in f=
uture
> > > 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 th=
is case will be difficult because the transaction is broadcasted after sign=
ing and before coinjoin tx broadcast.
> >
> > Inputs are already checked multiple times for double spend during coinj=
oin 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 use=
rs?
>
>
> Point is, the attacker is thousands of UTXOs can also DoS rounds by simpl=
y
> failing to complete the round. In fact, the double-spend DoS attack requi=
res
> 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