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

From: Peter Todd <[email-masked]>
Date: Tue, 4 Feb 2025 22:22:07 +0000

On Tue, Feb 04, 2025 at 03:02:01PM +0100, Yuval Kogman wrote:

I'm going to split this off because this kind of thing isn't relevant to
the actual technical details of interest to readers of their mailing
list, and I'll make it easy for the mods to decide whether or not to let
this part of the discussion through.

> # Conflict of Interest
> 
> It would have been appropriate for you to disclose that your review is
> paid for by an interested party as a direct response to accusations I
> have made:

The supermajority of the people posting on this mailing list are being
paid for their work. It would be silly to pre-face every single email
with "sponsored by Foo"; what you are replying to is just an email, not
my actual review publication, which I have not completed yet.

You yourself appear to be paid to work on the topic of on-chain privacy
via your employment at Spiral; I don't see you putting disclaimers about
that.

https://x.com/spiralbtc/status/1704905217974665340

For actual public publications I've made, in recent years I've generally
said who paid for them and under what terms:

https://petertodd.org/2024/one-shot-replace-by-fee-rate
https://petertodd.org/2024/covenant-dependent-layer-2-review
https://petertodd.org/2023/v3-transactions-review
https://petertodd.org/2023/drivechains#backstory

There's some other material on that blog where payment really isn't
clear to me and not discussed. E.g. material I (partly) wrote in one
form for a client and then reworked on my own time to be a blog post.
And obviously, everything I write is arguably commercial: my full-time
employment is Bitcoin-related consulting, and publishing is one of the
main ways I get work.

> - https://archive.is/cbffL
> - https://archive.is/BJCNG
> 
> Kruw has described his service as "free" and "trustless", despite earning
> revenues and despite the issues described here. Supporting evidence for
> this is in the unedited version of this reply.

Wasabi set the coordinator fee limit to 0% by default in the Jun 2024
release:

https://github.com/WalletWasabi/WalletWasabi/releases/tag/v2.0.8.1

Kruw's coordinator does not charge a coordinator fee.

Due to how Wasabi coinjoins work, coinjoins will almost always have some
small amount of sats left over that didn't decompose into standard
denominations after the transaction fee is paid. Those sats go to the
coordinator. The amounts involved are tiny, always less than the
transaction fee, as you can easily see on https://liquisabi.com/

For example, b4daaefbd53dd255a4d1507889df52fe1adcc970b5edaea1d9fc2b1c840f7367,
had 31,407sats of leftovers that went to the coordinator, out of
5,459,668,967 sats of outputs and a 104,289 sat transaction fee.

	31,407 / 5,459,668,967 = 0.0006%

I'll let others decide whether or not you're being dishonest by not
mentioning the tiny amounts involved, while simultanously claiming I'm
being dishonest by not mentioning in my email that (as usual) I'm
getting paid to work on this stuff.

In particular, remember that that fees are part of the coinjoin security
model: we *need* transactions to be costly enough to prevent sybil
attacks. If anyone with access to coins can just do infinite coinjoin
transactions at zero cost, we have a potential sybil attack problem.

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

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