Re: storing an explicit nonce

On Mon, 11 Oct 2021 at 22:15, Bruce Momjian <bruce(at)momjian(dot)us> wrote:

> > Yes, that's the direction that I was thinking also and specifically with
> > XTS as the encryption algorithm to allow us to exclude the LSN but keep
> > everything else, and to address the concern around the nonce/tweak/etc
> > being the same sometimes across multiple writes. Another thing to
> > consider is if we want to encrypt zero'd page. There was a point
> > brought up that if we do then we are encrypting a fair bit of very
> > predictable bytes and that's not great (though there's a fair bit about
> > our pages that someone could quite possibly predict anyway based on
> > table structures and such...). I would think that if it's easy enough
> > to not encrypt zero'd pages that we should avoid doing so. Don't recall
> > offhand which way zero'd pages were being handled already but thought it
> > made sense to mention that as part of this discussion.
>
> Yeah, I wanted to mention that. I don't see any security difference
> between fully-zero pages, pages with headers and no tuples, and pages
> with headers and only a few tuples. If any of those are insecure, they
> all are. Therefore, I don't see any reason to treat them differently.
>

We had to special case zero pages and not encrypt them because as far as I
can tell, there is no atomic way to extend a file and initialize it to
Enc(zero) in the same step.

--

Ants Aasma
Senior Database Engineerwww.cybertec-postgresql.com