Re: storing an explicit nonce

Greetings,

* Andres Freund (andres(at)anarazel(dot)de) wrote:
> On Thu, May 27, 2021, at 08:10, Bruce Momjian wrote:
> > On Wed, May 26, 2021 at 05:11:24PM -0700, Andres Freund wrote:
> > > On 2021-05-25 17:12:05 -0400, Bruce Momjian wrote:
> > > > If we used a block cipher instead of a streaming one (CTR), this might
> > > > not work because the earlier blocks can be based in the output of
> > > > later blocks.
> > >
> > > What made us choose CTR for WAL & data file encryption? I checked the
> > > README in the patchset and the wiki page, and neither seem to discuss
> > > that.
> > >
> > > The dangers around nonce reuse, the space overhead of storing the nonce,
> > > the fact that single bit changes in the encrypted data don't propagate
> > > seem not great? Why aren't we using something like XTS? It has obvious
> > > issues as wel, but CTR's weaknesses seem at least as great. And if we
> > > want a MAC, then we don't want CTR either.
> >
> > We chose CTR because it was fast, and we could use the same method for
> > WAL, which needs a streaming, not block, cipher.
>
> The WAL is block oriented too.

I'm curious what you'd suggest for the heap where we wouldn't be able to
have block chaining (at least, I presume we aren't talking about
rewriting entire segments whenever we change something in a heap).

Thanks,

Stephen