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Date: Tue, 14 Nov 2017 05:07:28 -0500
From: Peter Todd <pete@petertodd.org>
To: Gregory Maxwell <greg@xiph.org>,
Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Message-ID: <20171114100728.GA29749@savin.petertodd.org>
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Subject: Re: [bitcoin-dev] Updates on Confidential Transactions efficiency
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On Tue, Nov 14, 2017 at 01:21:14AM +0000, Gregory Maxwell via bitcoin-dev w=
rote:
> The primary advantage of this approach is that it can be constructed
> without any substantial new cryptographic assumptions (e.g., only
> discrete log security in our existing curve), that it can be high
> performance compared to alternatives, that it has no trusted setup,
> and that it doesn't involve the creation of any forever-growing
> unprunable accumulators. All major alternative schemes fail multiple
> of these criteria (e.g., arguably Zcash's scheme fails every one of
> them).
Re: the unprunable accumulators, that doesn't need to be an inherent proper=
ty
of Zcash/Monero style systems.
It'd be quite feasible to use accumulator epochs and either make unspent co=
ins
in a previous epoch unspendable after some expiry time is reached - allowing
the spent coin accumulator data to be discarded - or make use of a merkeliz=
ed
key-value scheme with transaction provided proofs to shift the costs of
maintaining the accumulator to wallets.
The disadvantage of epoch schemes is of course a reduced k-anonymity set, b=
ut
if I understand the Confidential Transactions proposals correctly, they alr=
eady
have a significantly reduced k-anonymity set per transaction than Zcash
theoretically could (modulo it's in practice low anonymity set due to lack =
of
actual usage). In that respect, epoch size is simply a tradeoff between sta=
te
size and k-anonymity set size.
--=20
https://petertodd.org 'peter'[:-1]@petertodd.org
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