Re: storing an explicit nonce

Greetings,

* Ants Aasma (ants(at)cybertec(dot)at) wrote:
> On Wed, 13 Oct 2021 at 02:20, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
> > On Wed, Oct 13, 2021 at 12:48:51AM +0300, Ants Aasma wrote:
> > > On Wed, 13 Oct 2021 at 00:25, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
> > >
> > > On Tue, Oct 12, 2021 at 11:21:28PM +0300, Ants Aasma wrote:
> > > > Page encrypting to all zeros is for all practical purposes
> > impossible to
> > > hit.
> > > > Basically an attacker would have to be able to arbitrarily set the
> > whole
> > > > contents of the page and they would then achieve that this page
> > gets
> > > ignored.
> > >
> > > Uh, how do we know that valid data can't produce an encrypted
> > all-zero
> > > page?
> > >
> > >
> > > Because the chances of that happening by accident are equivalent to
> > making a
> > > series of commits to postgres and ending up with the same git commit
> > hash 400
> > > times in a row.
> >
> > Yes, 256^8192 is 1e+19728, but why not just assume a page LSN=0 is an
> > empty page, and if not, an error? Seems easier than checking if each
> > page contains all zeros every time.
> >
>
> We already check it anyway, see PageIsVerifiedExtended().

Right- we check the LSN along with the rest of the page there.

Thanks,

Stephen