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Date: Tue, 31 Aug 2021 14:22:29 +0000
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To: Zac Greenwood <zachgrw@gmail.com>
From: ZmnSCPxj <ZmnSCPxj@protonmail.com>
Reply-To: ZmnSCPxj <ZmnSCPxj@protonmail.com>
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Cc: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Exploring: limiting transaction output amount as
a function of total input value
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X-List-Received-Date: Tue, 31 Aug 2021 14:22:45 -0000
Good morning Zac,
> Hi ZmnSCPxj,
>
> Thank you for your helpful response. We're on the same page concerning pr=
ivacy so I'll focus on that. I understand from your mail that privacy would=
be reduced by this proposal because:
>
> * It requires the introduction of a new type of transaction that is diffe=
rent from a "standard" transaction (would that be P2TR in the future?), red=
ucing the anonymity set for everyone;
> * The payment and change output will be identifiable because the change o=
utput must be marked encumbered on-chain;
> * The specifics of how the output is encumbered must be visible on-chain =
as well reducing privacy even further.
>
> I don't have the technical skills to judge whether these issues can someh=
ow be resolved. In functional terms, the output should be spendable in a wa=
y that does not reveal that the output is encumbered, and produce a change =
output that cannot be distinguished from a non-change output while still be=
ing encumbered. Perhaps some clever MAST-fu could somehow help?
I believe some of the covenant efforts may indeed have such clever MAST-fu =
integrated into them, which is why I pointed you to them --- the people dev=
eloping these (aj I think? RubenSomsen?) might be able to accommodate this =
or some subset of the desired feature in a sufficiently clever covenant sch=
eme.
There are a number of such proposals, though, so I cannot really point you =
to one that seems likely to have a lot of traction.
Regards,
ZmnSCPxj
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