linux-kernel - Re: [PATCH v3 4/7] crypto: AF

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Message-ID: <20141124142945.GB31469@gondor.apana.org.au>
Date:	Mon, 24 Nov 2014 22:29:46 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Stephan Mueller <smueller@...onox.de>
Cc:	Daniel Borkmann <dborkman@...hat.com>,
	'Quentin Gouchet' <quentin.gouchet@...il.com>,
	lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-crypto@...r.kernel.org, linux-api@...r.kernel.org
Subject: Re: [PATCH v3 4/7] crypto: AF_ALG: add AEAD support

On Fri, Nov 21, 2014 at 06:32:16AM +0100, Stephan Mueller wrote:
> This patch adds the AEAD support for AF_ALG.
> 
> The AEAD implementation uses the entire memory handling and
> infrastructure of the existing skcipher implementation.
> 
> To use AEAD, the user space consumer has to use the salg_type named
> "aead". The AEAD extension only uses the bind callback as the key
> differentiator. The previously added functions that select whether to
> use AEAD or ablkcipher crypto API functions depend on the TFM type
> allocated during the bind() call.
> 
> The addition of AEAD brings a bit of overhead to calculate the size of
> the ciphertext, because the AEAD implementation of the kernel crypto API
> makes implied assumption on the location of the authentication tag. When
> performing an encryption, the tag will be added to the created
> ciphertext (note, the tag is placed adjacent to the ciphertext). For
> decryption, the caller must hand in the ciphertext with the tag appended
> to the ciphertext. Therefore, the selection of the used memory
> needs to add/subtract the tag size from the source/destination buffers
> depending on the encryption type. The code is provided with comments
> explainint when and how that operation is performed.
> 
> Note: The AF_ALG interface does not support zero length input data.
> Such zero length input data may be used if one wants to access the hash
> implementation of an AEAD directly (e.g. the GHASH of GCM or CMAC for
> CCM). However, this is a use case that is not of interest. GHASH or
> CMAC is directly available via the hash AF_ALG interface and we
> therefore do not need to take precautions for this use case.
> 
> A fully working example using all aspects of AEAD is provided at
> http://www.chronox.de/libkcapi.html
> 
> Signed-off-by: Stephan Mueller <smueller@...onox.de>

I appreciate the effort to share code, but shoe-horning AEAD into
algif_skcipher is just too ugly.

How about let's just start with a separate algif_aead and then
add helpers to merge common code as applicable?

Thanks,
-- 
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
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