Re: [PATCH v3 4/7] crypto: AF_ALG: add AEAD support

[Herbert Xu]

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@xxxxxxxxxx>

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@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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