Why the auxiliary cipher in gss_krb5_crypto.c?

[Bruce Fields]

On Fri, Dec 04, 2020 at 04:01:53PM +0000, David Howells wrote:
> Bruce Fields <bfields at fieldses.org> wrote:
> 
> > > Reading up on CTS, I'm guessing the reason it's like this is that CTS is the
> > > same as the non-CTS, except for the last two blocks, but the non-CTS one is
> > > more efficient.
> > 
> > CTS is cipher-text stealing, isn't it?  I think it was Kevin Coffman
> > that did that, and I don't remember the history.  I thought it was
> > required by some spec or peer implementation (maybe Windows?) but I
> > really don't remember.  It may predate git.  I'll dig around and see
> > what I can find.
> 
> rfc3961 and rfc3962 specify CTS-CBC with AES.

OK, I guess I don't understand the question.  I haven't thought about
this code in at least a decade.  What's an auxilary cipher?  Is this a
question about why we're implementing something, or how we're
implementing it?

--b.