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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Thu, 17 Feb 2022 08:07:48 +0100
Message-ID: <CAK8P3a0AyNDRmzm8DOP2ieKtkXCJNEYdSVxzG5w-XmiZk3w+pg@mail.gmail.com>
Subject: Re: [RFC PATCH v2 1/7] crypto: xctr - Add XCTR support
To:     Eric Biggers <ebiggers@kernel.org>
Cc:     Nathan Huckleberry <nhuck@google.com>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@vger.kernel.org>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Paul Crowley <paulcrowley@google.com>,
        Sami Tolvanen <samitolvanen@google.com>,
        Ard Biesheuvel <ardb@kernel.org>
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On Thu, Feb 17, 2022 at 12:00 AM Eric Biggers <ebiggers@kernel.org> wrote:
> On Thu, Feb 10, 2022 at 11:28:06PM +0000, Nathan Huckleberry wrote:
> > diff --git a/crypto/Kconfig b/crypto/Kconfig
> > index fa1741bb568f..8543f34fa200 100644
> > --- a/crypto/Kconfig
> > +++ b/crypto/Kconfig
> > @@ -452,6 +452,15 @@ config CRYPTO_PCBC
> >         PCBC: Propagating Cipher Block Chaining mode
> >         This block cipher algorithm is required for RxRPC.
> >
> > +config CRYPTO_XCTR
> > +     tristate
> > +     select CRYPTO_SKCIPHER
> > +     select CRYPTO_MANAGER
> > +     help
> > +       XCTR: XOR Counter mode. This blockcipher mode is a variant of CTR mode
> > +       using XORs and little-endian addition rather than big-endian arithmetic.
> > +       XCTR mode is used to implement HCTR2.
>
> Now that this option isn't user-selectable, no one will see this help text.
> I think it would be best to remove it, and make sure that the comment in
> crypto/xctr.c fully explains what XCTR is (currently it's a bit inadequate).

I generally prefer to have a help text in Kconfig even for hidden symbols,
and I read those when trying to find my way through code I'm not familiar
with. It's probably a good idea to expand the comment in the source
file as well, but I would suggest leaving this one in here.

         Arnd