From: "Russell O'Connor" <roconnor@blockstream•io>
To: Anthony Towns <aj@erisian•com.au>,
Bitcoin Protocol Discussion
<bitcoin-dev@lists•linuxfoundation.org>
Subject: Re: [bitcoin-dev] Taproot: Privacy preserving switchable scripting
Date: Sat, 27 Jan 2018 12:07:25 -0500 [thread overview]
Message-ID: <CAMZUoKmfcmfgErhvAZUQgi8R7bzYCMotT7MMpqQrePej09NBmw@mail.gmail.com> (raw)
In-Reply-To: <20180123064419.GA1296@erisian.com.au>
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On Tue, Jan 23, 2018 at 1:44 AM, Anthony Towns via bitcoin-dev <
bitcoin-dev@lists•linuxfoundation.org> wrote:
> On Tue, Jan 23, 2018 at 12:30:06AM +0000, Gregory Maxwell via bitcoin-dev
> wrote:
> > One point that comes up while talking about merkelized scripts is can
> > we go about making fancier contract use cases as indistinguishable as
> > possible from the most common and boring payments.
>
> > Now we tweak C to produce P which is the key we'll publish: P = C +
> H(C||S)G.
> > (This is the attack hardened pay-to-contract construction described in
> [2])
> > Then we pay to a scriptPubKey of [Taproot supporting version] [EC point
> P].
>
> Is this really intended as paying directly to a pubkey, instead of a
> pubkey hash?
>
> If so, isn't that a step backwards with regard to resistance to quantum
> attacks against ECC?
>
> Paying direct to pubkey doesn't seem quite enough to make pay-to-taproot
> cheaper than p2wpkh: the extra 12 bytes in the scriptPubKey would need
> you to reduce the witness by 48 bytes to maintain the weight, but I think
> you'd only be saving 33 bytes by not having to reveal the pubkey, and
> another 6-7 bytes by having a tighter signature encoding than DER. Still,
> that's pretty close with a difference of only a couple of vbytes per
> input by my count.
>
I've been thinking about your comment, and I think your concern can be
addressed. Taproot would almost certainly be deployed in conjunction with
cross-input signature aggregation. Because aggregation doesn't work with
ECDSA, only those signatures using Taproot and other Schnorr signatures
would be available for aggregation. Just having the ability to support
cross-input signature aggregation may be motivation enough for ordinary
pub-key users to switch to Taproot. However, there is more.
Cross-input signature aggregation probably requires a new field to be added
to the P2P transaction structure to hold the aggregated signature, since
there isn't really a good place to put it in the existing structure (there
are games you can play to make it fit, but I think it is worthwhile). The
obvious way add block commitments to a new tx field is via the witness
reserved value mechanism present in BIP 141. At this point I think there
will be some leeway to adjust the discount on the weight of this new
aggregated signature tx field so that even a single input taproot using the
aggregated signature system (here an aggregation of 1 signature) ends up no
more expensive than a single input segwit P2WPKH.
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next prev parent reply other threads:[~2018-01-27 17:07 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-23 0:30 Gregory Maxwell
2018-01-23 1:55 ` Chris Belcher
2018-01-23 2:51 ` Matt Corallo
2018-01-23 14:39 ` Mark Friedenbach
2018-01-23 21:23 ` Matt Corallo
2018-01-23 21:38 ` Gregory Maxwell
2018-01-23 6:44 ` Anthony Towns
2018-01-23 13:15 ` Gregory Maxwell
2018-01-23 22:22 ` Anthony Towns
2018-01-23 22:45 ` Gregory Maxwell
2018-01-24 1:52 ` Andrew Poelstra
2018-01-24 9:28 ` Tim Ruffing
2018-01-24 12:51 ` Natanael
2018-01-24 15:38 ` Tim Ruffing
2018-01-24 18:51 ` Natanael
2018-01-24 23:22 ` Tim Ruffing
2018-01-25 0:09 ` Natanael
2018-01-26 13:14 ` [bitcoin-dev] Recovery of old UTXOs in a post-quantum world Tim Ruffing
2018-01-27 17:07 ` Russell O'Connor [this message]
2018-01-27 17:23 ` [bitcoin-dev] Taproot: Privacy preserving switchable scripting Matt Corallo
2018-01-23 15:43 ` Greg Sanders
2018-01-26 21:34 ` Gregory Maxwell
2018-07-13 1:51 ` [bitcoin-dev] Generalised taproot Anthony Towns
2018-10-24 2:22 ` Pieter Wuille
2018-02-05 9:27 ` [bitcoin-dev] Taproot: Privacy preserving switchable scripting ZmnSCPxj
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