linux-kernel - Re: [PATCH 4/6] crypto: hkdf - RFC5869 Key Derivation Function

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Message-ID: <20190112095535.36rh3ptnrf7yxacv@gondor.apana.org.au>
Date:   Sat, 12 Jan 2019 17:55:35 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     Stephan Müller <smueller@...onox.de>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        Andy Lutomirski <luto@...capital.net>,
        "Lee, Chun-Yi" <joeyli.kernel@...il.com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Pavel Machek <pavel@....cz>, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, keyrings@...r.kernel.org,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Chen Yu <yu.c.chen@...el.com>,
        Oliver Neukum <oneukum@...e.com>,
        Ryan Chen <yu.chen.surf@...il.com>,
        David Howells <dhowells@...hat.com>,
        Giovanni Gherdovich <ggherdovich@...e.cz>,
        Randy Dunlap <rdunlap@...radead.org>,
        Jann Horn <jannh@...gle.com>,
        Andy Lutomirski <luto@...nel.org>, linux-crypto@...r.kernel.org
Subject: Re: [PATCH 4/6] crypto: hkdf - RFC5869 Key Derivation Function

On Fri, Jan 11, 2019 at 09:12:54PM -0800, Eric Biggers wrote:
> Hi Stephan,
> 
> On Fri, Jan 11, 2019 at 08:10:39PM +0100, Stephan Müller wrote:
> > The RFC5869 compliant Key Derivation Function is implemented as a
> > random number generator considering that it behaves like a deterministic
> > RNG.
> > 
> 
> Thanks for the proof of concept!  I guess it ended up okay.  But can you explain
> more the benefits of using the crypto_rng interface, as opposed to just some
> crypto_hkdf_*() helper functions that are exported for modules to use?

I agree.  I see no benefit in adding this through the RNG API as
opposed to just providing it as a helper.  If some form of hardware
acceleration were to eventuate in the future we could always revisit
this.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt