Re: storing an explicit nonce

Hi,

On Thu, May 27, 2021, at 08:10, Bruce Momjian wrote:
> On Wed, May 26, 2021 at 05:11:24PM -0700, Andres Freund wrote:
> > Hi,
> > 
> > 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.

Andres