Date: Tue, 10 May 2022 16:54:31 +0000
To: AdamISZ <AdamISZ@protonmail.com>,
 Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
From: ZmnSCPxj <ZmnSCPxj@protonmail.com>
Reply-To: ZmnSCPxj <ZmnSCPxj@protonmail.com>
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Subject: Re: [bitcoin-dev] BIP proposal: Timelocked address fidelity bond
	for BIP39 seeds
Precedence: list

Good morning waxwing,

> ------- Original Message -------
> On Sunday, May 1st, 2022 at 11:01, Chris Belcher via bitcoin-dev bitcoin-=
dev@lists.linuxfoundation.org wrote:
>
> > Hello ZmnSCPxj,
> > This is an intended feature. I'm thinking that the same fidelity bond
> > can be used to running a JoinMarket maker as well as a Teleport
> > (Coinswap) maker.
> > I don't believe it's abusable. It would be a problem if the same
> > fidelity bond is used by two makers in the same application, but
> > JoinMarket takers are already coded to check for this, and Teleport
> > takers will soon as well. Using the same bond across different
> > applications is fine.
> > Best,
> > CB
>
> Hi Chris, Zmn, list,
> I've noodled about this a few times in the past (especially when trying t=
o figure out an LSAG style ring sig based FB for privacy, but that does not=
 seem workable), and I can't decide the right perspective on it.
>
> A user sacrifices X amount of time-value-of-money (henceforth TVOM) by co=
mmitting in Joinmarket with FB1. He then uses the same FB1 in Teleport, let=
's say. If he gets benefit Y from using FB1 in Joinmarket, and benefit Z in=
 Teleport, then presumably he'll only do it if (probabilistically) he think=
s Y+Z > X.
>
> But as an assessor of FB1 in Joinmarket, I don't know if it's also being =
used for Teleport, and more importantly, if it's being used somewhere else =
I'm not even aware of. Now I'm not an economist I admit, so I might not be =
intuit-ing this situation right, but it fees to me like the right answer is=
 "It's fine for a closed system, but not an open one." (i.e. if the set of =
possible usages is not something that all participants have fixed in advanc=
e, then there is an effective Sybilling problem, like I'm, as an assessor, =
thinking that sacrificed value 100 is there, whereas actually it's only 15,=
 or whatever.)
>
> As I mentioned in https://github.com/JoinMarket-Org/joinmarket-clientserv=
er/issues/993#issuecomment-1110784059 , I did wonder about domain separatio=
n tags because of this, and as I vaguely alluded to there, I'm really not s=
ure about it.
>
> If it was me I'd want to include domain separation via part of the signed=
 message, since I don't see how it hurts? For scenarios where reuse is fine=
, reuse can still happen.

Ah, yes, now I remember.
I discussed this with Tamas as well in the past and that is why we conclude=
d that in defiads, each UTXO can host at most one advertisement at any one =
time.
In the case of defiads there would be a sequence counter where a higher-seq=
uenced advertisement would replace lower-sequenced advertisement, so you co=
uld update, but at any one time, for a defiads node, only one advertisement=
 per UTXO could be used.
This assumed that there would be a defiads network with good gossip propaga=
tion so our thinking at the time was that a higher-sequenced advertisement =
would quickly replace lower-sequenced ones on the network.
But it is simpler if such replacement would not be needed, and you could th=
en commit to the advertisement directly on the UTXO via a tweak.

Each advertisement would also have a specific application ID that it applie=
d to, and applications on top of defiads would ask the local defiads node t=
o give it the ads that match a specific application ID, so a UTXO could onl=
y be used for one application at a time.
This would be equivalent to domain separation tags that waxwing mentions.

Regards,
ZmnSCPxj