> 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
deduce, but often, far from impossible).

Yes sure that's a good point, it may affect protocol too if your LN
implementation has its own onchain wallet. If not, and it reuses a non-LN
wallet you just carry on its fingerprint.
An extension in the future could be for closing/splicing transaction, your
liquidity algorithm may select in a really specific fashion which channels
must be closed or increased...

> But I would ask people to consider CoinJoinXT[1] more seriously in a
taproot/schnorr world, since it addresses this exact point.

The equal value paradigm is such a watermark and I assume it leans to
increase the number of outputs so I don't see it followed by any other
protocol. But yes CoinjoinXT, if you can come up with a easy interactive
multi-tx construction protocol that would be interesting (and could be
reused by any cut-through implementation I guess).

Overall, my thinking was to start specifying this now because such thing
would take a fair amount of time/coordination to get adopted. This way if
and when Taproot/Schnorr happen we don't
have to wait another period to start enjoying the privacy enhancement
(worst-case we can fallback on 2p-ecdsa).



Le sam. 22 févr. 2020 à 07:10, AdamISZ <AdamISZ@protonmail.com> a écrit :

> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> On Friday, 21 February 2020 22:17, Antoine Riard via bitcoin-dev <
> bitcoin-dev@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
> deduce, 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
> broader), my comment is:
> For existing protocols (joinmarket's, wasabi's, samourai's), in the
> equal-outs 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
> taproot/schnorr world, since it addresses this exact point. With a short
> (not cross-block like swaps or LN setup) interaction, participants can
> arrange the effect of coinjoin without the on-chain watermark of coinjoin
> (so, steganographic). The taproot/schnorr part is needed there because
> multisig is required 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/
>