Subject: Re: [bitcoindev] Reiterating centralized coinjoin (Wasabi & Samourai) deanonymization attacks

From: Javier Mateos <[email-masked]>
Date: Mon, 7 Apr 2025 03:01:39 -0700 (PDT)

Hello everyone,

First of all, I believe this debate has been extremely constructive, 
despite some friction regarding inherent biases. I think Yuval has 
identified real risks, and at the same time, there was a lack of clarity 
regarding how the coordinator operated. If the coordinator had malicious 
intentions in the beginning, these have been observed and brought to the 
table by a community that is always active and vigilant about these crucial 
issues. I believe this is already part of the healthy culture surrounding 
Bitcoin.

At this moment, what is crucial is to look forward and demand:

-Overall Transparency: We need clear answers to questions such as: How are 
the residual funds calculated and allocated? Which wallet(s) are used? 
Ultimately, this information should be publicly verifiable on the 
blockchain.

-Audit and Review of the Revenue Model: Is the current mechanism (which 
retains residual funds) the best option? Could the excess be redistributed 
among users? Should it be handed over to a group of independent auditors, 
or what alternative is best? These are questions aimed at finding more 
transparent options, especially if disclosed properly. They could even be 
addressed through a bounty, for example.

-Audit and Review of the Protocol Architecture: The measures above would 
help and could pave the way for the adoption of technical mitigations.

Clearly, a thorough technical and ethical review is required, or else we 
wouldn’t have this healthy debate.

Regards,

-Javier

El viernes, 4 de abril de 2025 a las 14:26:17 UTC-3, Peter Todd escribió:

> On Fri, Jan 31, 2025 at 10:39:10PM +0100, Yuval Kogman wrote:
> > - https://youtu.be/v952Fd1vmOs?t=2073 - here, months after launching
> > his service, he fails to disclose until pressed to elaborate, then
> > admits he's collecting revenues and casually misrepresents the
> > "optimistic" behavior of wasabi (which a bug) as a "little known
> > secret" that justifies his appropriation of excess funds, which under
> > the zksnacks coordinator went to the mining fees (thereby bolstering
> > sybil resistance, not undermining it).
>
> For the record, I checked the archive.org and github history of the
> Wasabi Wallet docs themselves, and since at least Nov 23rd 2024
> (archive.org) or possible Oct 10th 2024 (git commit), they've clearly
> stated that leftovers go to the coordinator:
>
> "In rare cases the output decomposition contains change (maximum of
> 10,000 sats per coinjoin), this leftover goes to the coordinator. This
> is because creating such small amounts would harm privacy and ends up
> being more expensive than just forfeiting it."
>
> (note: this whole passage is highlighted)
>
>
> https://web.archive.org/web/20241123035844/https://docs.wasabiwallet.io/using-wasabi/CoinJoin.html#fees
>
> https://github.com/WalletWasabi/WasabiDoc/commit/a1f2f474f282918f2e1626a01351ac8f1b9c43cf
>
> The git commit that introduced that language is PGP-signed by Github as
> of Nov 9th 2024.
>
> -- 
> https://petertodd.org 'peter'[:-1]@petertodd.org
>

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