Date: Wed, 24 Jan 2018 01:52:57 +0000
From: Andrew Poelstra <apoelstra@wpsoftware.net>
To: Gregory Maxwell via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org>
Message-ID: <20180124015256.GR9082@boulet.lan>
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Subject: Re: [bitcoin-dev] Taproot: Privacy preserving switchable scripting
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On Tue, Jan 23, 2018 at 10:45:06PM +0000, Gregory Maxwell via bitcoin-dev w=
rote:
> On Tue, Jan 23, 2018 at 10:22 PM, Anthony Towns <aj@erisian.com.au> wrote:
> > Hmm, at least people can choose not to reuse addresses currently --
> > if everyone were using taproot and that didn't involve hashing the key,
>=20
> Can you show me a model of quantum computation that is conjectured to
> be able to solve the discrete log problem but which would take longer
> than fractions of a second to do so? Quantum computation has to occur
> within the coherence lifetime of the system.
>=20
> > way for individuals to hedge against quantum attacks in case they're ev=
er feasible, at least that I can see (well, without moving their funds out =
of bitcoin anyway)?
>=20
> By using scriptpubkeys with actual security against quantum computers
> instead of snake-oil.
>=20
> > (It seems like using the point at infinity wouldn't work because
>=20
> Indeed, that doesn't work.
>=20
> > that when quantum attacks start approaching feasibility. If funds are
> > being held in reused addresses over the long term, that would be more
>=20
> They are. But I don't believe that is relevant; the attacker would
> simply steal the coins on spend.


Then the system would need to be hardforked to allow spending through a
quantum-resistant ZKP of knowledge of the hashed public key. I expect
that in a post-quantum world there will be demand for such a fork,
especially if we came into such a world through surprise evidence of
a discrete log break.

--=20
Andrew Poelstra
Mathematics Department, Blockstream
Email: apoelstra at wpsoftware.net
Web:   https://www.wpsoftware.net/andrew

"A goose alone, I suppose, can know the loneliness of geese
 who can never find their peace,
 whether north or south or west or east"
       --Joanna Newsom


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