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Date:   Fri, 14 May 2021 16:05:53 +0800
From:   Herbert Xu <herbert@gondor.apana.org.au>
To:     Eric Biggers <ebiggers@kernel.org>
Cc:     Mike Brooks <m@ib.tc>, Ard Biesheuvel <ardb@kernel.org>,
        Kestrel seventyfour <kestrelseventyfour@gmail.com>,
        Linux Crypto Mailing List <linux-crypto@vger.kernel.org>
Subject: Re: or should block size for xts.c set to 1 instead of AES block
 size?
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On Tue, May 11, 2021 at 12:31:17PM -0700, Eric Biggers wrote:
>
> Well, the problem is that it isn't well defined what the cra_blocksize property
> actually means.  Depending on the algorithm, it can mean either the minimum
> input size, the required alignment of the input size, the exact input size that
> is required (in the case of block ciphers), or the input size that is required
> by the algorithm's internal compression function (in the case of hashes).
> 
> "xts" follows the convention of cra_blocksize meaning the "minimum input size",
> as do "cts" and "adiantum" which have the same constraints on input sizes as
> "xts".
> 
> So I'm not sure that changing cra_blocksize for xts to 1 would accomplish
> anything useful, other than confuse things further.

At this point we can't change the blocksize of cts/xts to 1 without
breaking af_alg because it needs to treat them differently than it
would for a stream cipher like ctr.

But to properly support af_alg on cts/xts we do need to do this.
I have a patch-set that adds the final chunk size to do exactly
that but I haven't had the time to finish it.

Cheers,
-- 
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