linux-kernel - Re: Why the auxiliary cipher in gss_krb5

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Message-ID: <20201204160347.GA26933@fieldses.org>
Date:   Fri, 4 Dec 2020 11:03:47 -0500
From:   Bruce Fields <bfields@...ldses.org>
To:     David Howells <dhowells@...hat.com>
Cc:     Chuck Lever <chuck.lever@...cle.com>,
        CIFS <linux-cifs@...r.kernel.org>,
        Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        linux-crypto@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-afs@...ts.infradead.org
Subject: Re: Why the auxiliary cipher in gss_krb5_crypto.c?

On Fri, Dec 04, 2020 at 04:01:53PM +0000, David Howells wrote:
> Bruce Fields <bfields@...ldses.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.