Date: Sat, 22 Feb 2020 12:10:52 +0000
To: Antoine Riard <antoine.riard@gmail.com>,
 Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
From: AdamISZ <AdamISZ@protonmail.com>
Reply-To: AdamISZ <AdamISZ@protonmail.com>
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Subject: Re: [bitcoin-dev] LN & Coinjoin, a Great Tx Format Wedding
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=E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90 Original Me=
ssage =E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90
On Friday, 21 February 2020 22:17, Antoine Riard via bitcoin-dev <bitcoin-d=
ev@lists.linuxfoundation.org> wrote:

> How can a Bitcoin tranaction leak protocol usage ?
> * the output type (p2sh, p2wsh, ...)
> * the spending policy (2-of-3 multisig, timelock, hashlock,...)
> * outputs ordering (BIP69)
> * nLocktime/nSequence
> * RBF-signaling
> * Equal-value outputs
> * weird watermark (LN commitment tx obfuscated commitment number)
> * fees strategy like CPFP
> * in-protocol announcements [0]
>
Good list.
Another one, usually wouldn't be *protocol* as much as wallet leakage, but =
could be: utxo selection algorithm (which of course may be difficult to ded=
uce, but often, far from impossible).
(Also trivial and increasingly irrelevant, but nVersion).

With regards to coinjoin in this context (I know your points are much broad=
er), my comment is:
For existing protocols (joinmarket's, wasabi's, samourai's), in the equal-o=
uts paradigm, I don't see much that can be done in this area.
But I would ask people to consider CoinJoinXT[1] more seriously in a taproo=
t/schnorr world, since it addresses this exact point. With a short (not cro=
ss-block like swaps or LN setup) interaction, participants can arrange the =
effect of coinjoin without the on-chain watermark of coinjoin (so, steganog=
raphic). The taproot/schnorr part is needed there because multisig is requi=
red from transaction to transaction in that protocol, so doing it today is =
less interesting (albeit still interesting).

waxwing

[1] https://joinmarket.me/blog/blog/coinjoinxt/