Re: [PATCH] crypto: add key wrapping block chaining mode

[Stephan Mueller <smueller@chronox.de>]

Am Freitag, 24. April 2015, 07:21:05 schrieb Herbert Xu:

Hi Herbert,

>On Thu, Apr 23, 2015 at 03:42:19PM +0200, Stephan Mueller wrote:
>> Now, shall I kind of re-implement the chainiv ablkcipher wrapper into an IV
>> handler that just helps my code? That will be a lot of code for a simple
>> memcmp.
>
>No no no.  You don't need to do a template for givencrypt.  chainiv
>is a template because it can be used by any blkcipher.  In your case
>your fixed IV is only used by you.  So just implement givencrypt and
>givdecrypt directly in your blkcipher (or ablkcipher rather because
>only ablkcipher supports givencrypt/givdecrypt).
>
>If you really want to keep the underlying kw as a blkcipher for the
>sake of simplicity you could go back to the wrapper idea and have
>the rfc wrapper around kw as an ablkcipher so that you can add the
>givencrypt/givdecrypt calls.

For the moment, I was working on the following approach:

- kw() as blkcipher (like ctr()

- implement a kwiv geniv handler and use it by kw via:

	inst->alg.cra_blkcipher.geniv = "kwiv";



So, if I read your recommendation right, I would do the following:

- kw() as blkcipher (like the ctr())

- rfc3394() as ablkcipher around kw (like rfc3686())

I also have the givencrypt and givdecrypt functions. How would I directly hook 
them into the ablkcipher without using a reference for inst-
>alg.cra_ablkcipher.geniv?


Which approach would fit best?


Ciao
Stephan