Luke, do you mean to replace the first 4 bytes of the second chunk (bytes
64..67 in 0-based counting) by the XOR of those 4 bytes with the first 4
bytes of the midstate? (I assume you don't care about 12 bytes but rather
those 4 bytes.)

This does not work. All it does is adding another computational step before
you can check for a collision in those 4 bytes. It makes finding a
collision only marginally harder.

On Wed, May 11, 2016 at 7:28 AM, Luke Dashjr via bitcoin-dev <
bitcoin-dev@lists.linuxfoundation.org> wrote:

> On Wednesday, May 11, 2016 12:20:55 PM Sergio Demian Lerner via bitcoin-dev
> wrote:
> > On Tue, May 10, 2016 at 6:43 PM, Sergio Demian Lerner <
> > sergio.d.lerner@gmail.com> wrote:
> > > You can find it here:
> > >
> https://bitslog.wordpress.com/2014/03/18/the-re-design-of-the-bitcoin-blo
> > > ck-header/
> > >
> > > Basically, the idea is to put in the first 64 bytes a 4 byte hash of
> the
> > > second 64-byte chunk. That design also allows increased nonce space in
> > > the first 64 bytes.
> >
> > My mistake here. I didn't recalled correctly my own idea. The idea is to
> > include in the second 64-byte chunk a 4-byte hash of the first chunk, not
> > the opposite.
>
> What if we XOR bytes 64..76 with the first 12 bytes of the SHA2 midstate?
> Would that work?
>
> Luke
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