Re: storing an explicit nonce

On Tue, May 25, 2021 at 04:29:08PM -0400, Stephen Frost wrote:
> Greetings,
>
> On Tue, May 25, 2021 at 14:56 Bruce Momjian <bruce(at)momjian(dot)us> wrote:
>
> On Tue, May 25, 2021 at 02:25:21PM -0400, Robert Haas wrote:
> > One question here is whether we're comfortable saying that the nonce
> > is entirely constant. I wasn't sure about that. It seems possible to
> > me that different encryption algorithms might want nonces of different
> > sizes, either now or in the future. I am not a cryptographer, but that
> > seemed like a bit of a limiting assumption. So Bharath and I decided
> > to make the POC cater to a fully variable-size nonce rather than
> > zero-or-some-constant. However, if the consensus is that
> > zero-or-some-constant is better, fair enough! The patch can certainly
> > be adjusted to cater to work that way.
>
> A 16-byte nonce is sufficient for AES and I doubt we will need anything
> stronger than AES256 anytime soon.  Making the nonce variable length
> seems it is just adding complexity for little purpose.
>
>
> I’d like to review this more and make sure using the special space is possible
> but if it is then it opens up a huge new possibility that we could use it for
> both the nonce AND an appropriately sized tag, giving us integrity along with
> encryption which would be a very significant additional feature.  I’d
> considered using a fork instead but having it on the page would be far better.

We already discussed that there are too many other ways to break system
integrity that are not encrypted/integrity-checked, e.g., changes to
clog. Do you disagree?

--
Bruce Momjian <bruce(at)momjian(dot)us> https://momjian.us
EDB https://enterprisedb.com

If only the physical world exists, free will is an illusion.