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From:   Ard Biesheuvel <ardb@kernel.org>
Date:   Wed, 20 May 2020 09:09:44 +0200
Message-ID: <CAMj1kXGNqo=d-hgK=0zBZCoJYgSxxhhm=Jdk2gAGXPo1-KSCgA@mail.gmail.com>
Subject: Re: [RFC/RFT PATCH 0/2] crypto: add CTS output IVs for arm64 and testmgr
To:     Stephan Mueller <smueller@chronox.de>
Cc:     Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Eric Biggers <ebiggers@kernel.org>
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On Wed, 20 May 2020 at 09:01, Stephan Mueller <smueller@chronox.de> wrote:
>
> Am Mittwoch, 20. Mai 2020, 08:54:10 CEST schrieb Ard Biesheuvel:
>
> Hi Ard,
>
> > On Wed, 20 May 2020 at 08:47, Stephan Mueller <smueller@chronox.de> wrote:
...
> > > The state of all block chaining modes we currently have is defined with
> > > the
> > > IV. That is the reason why I mentioned it can be implemented stateless
> > > when I am able to get the IV output from the previous operation.
> >
> > But it is simply the same as the penultimate block of ciphertext. So
> > you can simply capture it after encrypt, or before decrypt. There is
> > really no need to rely on the CTS transformation to pass it back to
> > you via the buffer that is only specified to provide an input to the
> > CTS transform.
>
> Let me recheck that as I am not fully sure on that one. But if it can be
> handled that way, it would make life easier.

Please refer to patch 2. The .iv_out test vectors were all simply
copied from the appropriate offset into the associated .ctext member.