From: Andrew Poelstra <apoelstra@wpsoftware•net>
To: Luke Dashjr <luke@dashjr•org>,
Bitcoin Protocol Discussion
<bitcoin-dev@lists•linuxfoundation.org>
Subject: Re: [bitcoin-dev] PSA: Taproot loss of quantum protections
Date: Mon, 15 Mar 2021 23:12:18 +0000 [thread overview]
Message-ID: <YE/p0u3gp4UYNS7R@camus> (raw)
In-Reply-To: <202103152148.15477.luke@dashjr.org>
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On Mon, Mar 15, 2021 at 09:48:15PM +0000, Luke Dashjr via bitcoin-dev wrote:
> Also, what I didn't know myself until today, is that we do not actually gain
> anything from this: the features proposed to make use of the raw keys being
> public prior to spending can be implemented with hashed keys as well.
> It would use significantly more CPU time and bandwidth (between private
> parties, not on-chain), but there should be no shortage of that for anyone
> running a full node (indeed, CPU time is freed up by Taproot!); at worst, it
> would create an incentive for more people to use their own full node, which
> is a good thing!
>
"No gain" except to save significant CPU time and bandwidth? As Matt points
out there is also a storage hit (unless you want to _really_ waste CPU time
by using pubkey recovery, eliminating any hope of batch validation while
introducing a new dependency on an algorithm with a very unclear patent
story).
Having exposed keys also lets you do ring signatures over outputs, creating the
ability to do private proof of funds via Provisions.
> Despite this, I still don't think it's a reason to NACK Taproot: it should be
> fairly trivial to add a hash on top in an additional softfork and fix this.
>
This would make Bitcoin strictly worse.
> In addition to the points made by Mark, I also want to add two more, in
> response to Pieter's "you can't claim much security if 37% of the supply is
> at risk" argument. This argument is based in part on the fact that many
> people reuse Bitcoin invoice addresses.
>
37% is a dramatic understatement. Every address which is derived using BIP32
should be assumed compromised to a QC attacker because xpubs are not treated
like secret key material and are trivial to e.g. extract from hardware wallets
or PSBTs. I expect the real number is close to 100%.
In any case, Taproot keys, when used according to the recommendation in
BIP-0341, are already hashes of their internal keys, so (a) Taproot outputs
actually have better quantum resistance than legacy outputs; and (b) adding
another hash would be strictly redundant.
--
Andrew Poelstra
Director of Research, Blockstream
Email: apoelstra at wpsoftware.net
Web: https://www.wpsoftware.net/andrew
The sun is always shining in space
-Justin Lewis-Webster
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next prev parent reply other threads:[~2021-03-15 23:18 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-15 21:48 Luke Dashjr
2021-03-15 22:05 ` Matt Corallo
2021-03-15 22:30 ` Robert Spigler
2021-03-15 22:40 ` Jeremy
2021-03-15 22:48 ` Matt Corallo
2021-03-15 23:01 ` Karl-Johan Alm
2021-03-15 23:19 ` Matt Corallo
2021-03-15 23:46 ` Lloyd Fournier
2021-03-16 0:50 ` Anthony Towns
2021-03-16 2:38 ` ZmnSCPxj
2021-03-16 3:44 ` Luke Dashjr
2021-03-16 13:28 ` Andrew Poelstra
2021-03-16 17:25 ` Matt Corallo
2021-03-17 1:23 ` Ryan Grant
2021-03-17 11:56 ` Eoin McQuinn
2021-03-15 23:12 ` Andrew Poelstra [this message]
2021-03-16 14:10 ` Andrea
2021-03-16 15:15 ` [bitcoin-dev] Provisions (was: PSA: Taproot loss of quantum protections) Andrew Poelstra
2021-03-17 4:24 ` ZmnSCPxj
2021-03-17 8:29 ` Andrea
2021-03-20 16:31 ` Andrea Barontini
2021-03-16 0:24 ` [bitcoin-dev] PSA: Taproot loss of quantum protections David A. Harding
2021-04-05 0:27 ` Lloyd Fournier
2021-04-16 3:47 ` ZmnSCPxj
2021-04-16 5:00 ` Lloyd Fournier
2021-03-22 14:24 ` Erik Aronesty
2021-03-23 9:36 ` Martin Schwarz
2021-03-23 10:50 ` Tim Ruffing
2021-08-12 22:08 ` Erik Aronesty
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