Received-SPF: pass (google.com: best guess record for domain of linux-crypto-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Thu, 20 Jun 2019 09:17:53 +0800
From:   Herbert Xu <herbert@gondor.apana.org.au>
To:     Eric Biggers <ebiggers@kernel.org>
Cc:     Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        linux-crypto@vger.kernel.org, dm-devel@redhat.com,
        linux-fscrypt@vger.kernel.org,
        Gilad Ben-Yossef <gilad@benyossef.com>,
        Milan Broz <gmazyland@gmail.com>
Subject: Re: [PATCH v3 1/6] crypto: essiv - create wrapper template for ESSIV
 generation
Message-ID: <20190620011752.et6clrrrbl5llgr2@gondor.apana.org.au>
References: <20190619162921.12509-1-ard.biesheuvel@linaro.org>
 <20190619162921.12509-2-ard.biesheuvel@linaro.org>
 <20190620010417.GA722@sol.localdomain>
 <20190620011325.phmxmeqnv2o3wqtr@gondor.apana.org.au>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20190620011325.phmxmeqnv2o3wqtr@gondor.apana.org.au>
User-Agent: NeoMutt/20170113 (1.7.2)
Sender: linux-crypto-owner@vger.kernel.org
Precedence: bulk

On Thu, Jun 20, 2019 at 09:13:25AM +0800, Herbert Xu wrote:
> On Wed, Jun 19, 2019 at 06:04:17PM -0700, Eric Biggers wrote:
> >
> > > +#define ESSIV_IV_SIZE		sizeof(u64)	// IV size of the outer algo
> > > +#define MAX_INNER_IV_SIZE	16		// max IV size of inner algo
> > 
> > Why does the outer algorithm declare a smaller IV size?  Shouldn't it just be
> > the same as the inner algorithm's?
> 
> In general we allow outer algorithms to have distinct IV sizes
> compared to the inner algorithm.  For example, rfc4106 has a
> different IV size compared to gcm.
> 
> In this case, the outer IV size is the block number so that's
> presumably why 64 bits is sufficient.  Do you forsee a case where
> we need 128-bit block numbers?

Actually this reminds me, the essiv template needs to be able to
handle multiple blocks/sectors, as otherwise this will still only
be able to push a single block/sector to the hardware at a time.

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