Re: storing an explicit nonce

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Stephen Frost <sfrost(at)snowman(dot)net>
Cc: Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Masahiko Sawada <masahiko(dot)sawada(at)2ndquadrant(dot)com>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Robert Haas <robertmhaas(at)gmail(dot)com>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Tom Kincaid <tomjohnkincaid(at)gmail(dot)com>
Subject: Re: storing an explicit nonce
Date: 2021-05-25 21:04:56
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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>

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

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