Hi Tim,

Just read through your post, thanks for the heads up - I only just joined
this mailing list.

In a post-quantum world, your second "d" type transaction is completely
forgeable, which means it is vulnerable to front-running. An adversary
capable of breaking ECDSA needs only listen for these transactions, obtain
"classic_sk" and then use a higher fee (or relationship with a miner) to
effectively turn your original "d" transaction into a double-spend, with
the forged transaction sending all your funds to the adversary.

I'm pretty confident that a PQ DSA is required to prevent front-running,
and that no "commit-reveal" scheme will be secure without one.

The other issue with your approach is that if it is rolled out today, it
will effectively double transaction volumes - this is what I tried to solve
in solutions 2 and 3 in my article by instead modifying the address
generation process.

Regards,

Tristan

On Tue, Feb 13, 2018 at 2:50 AM, Tim Ruffing via bitcoin-dev <
bitcoin-dev@lists.linuxfoundation.org> wrote:

> Hi Tristan,
>
> Regarding the "Post-Quantum Address Recovery" part (I haven't read the
> other parts), you may be interested in my message to the list from last
> month and the rest of the thread:
> https://lists.linuxfoundation.org/pipermail/bitcoin-dev/
> 2018-January/015659.html
>
> This is an approach which aims to avoid the issues that you've
> mentioned in your blog post.
>
> Best,
> Tim
>
> On Tue, 2018-02-13 at 01:13 +1100, Tristan Hoy via bitcoin-dev wrote:
> > Hi all,
> >
> > Recently I've been exploring what a post-quantum attack on Bitcoin
> > would actually look like, and what options exist for mitigating it.
> >
> > I've put up a draft of my research here: https://medium.com/@tristanh
> > oy/11271f430c41
> >
> > In summary:
> > 1) None of the recommended post-quantum DSAs (XMSS, SPHINCS) are
> > scalable
> > 2) This is a rapidly advancing space and committment to a specific
> > post-quantum DSA now would be premature
> > 3) I've identified a strategy (solution 3 in the draft) that
> > mitigates against the worst case scenario (unexpectedly early attack
> > on ECDSA) without requiring any changes to the Bitcoin protocol or
> > total committment to a specific post-quantum DSA that will likely be
> > superseded in the next 3-5 years
> > 4) This strategy also serves as a secure means of transferring
> > balances into a post-quantum DSA address space, even in the event
> > that ECDSA is fully compromised and the transition is reactionary
> >
> > The proposal is a change to key generation only and will be
> > implemented by wallet providers.
> >
> > Feedback would be most appreciated.
> >
> > Regards,
> >
> > Tristan
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