Re: Moving from blkcipher to skcipher

[Stephan Mueller <smueller@chronox.de>]

Am Montag, 3. Oktober 2016, 10:58:03 CEST schrieb Alex Cope:

Hi Alex,

> I was unclear in my initial message. I'm implementing a block cipher
> mode of operation. I'm hoping there is a another block cipher mode of
> operation that already uses skcipher, so I can use it as a reference
> and avoid re-inventing the wheel. In particular, it would be helpful
> if there is some implementation of a block cipher mode of operation
> that is directly above the underlying block cipher, like CTR or CBC,
> rather than something like CTS or rfc3686 which wrap around another
> block cipher mode of operation.

See gcm.c with the implementation referenced with crypto_gcm_base_tmpl or 
crypto_gcm_tmpl -- it uses the aead API which is conceptually similar to the 
skcipher API. And again you see the same concept applied as in the example I 
provided below. 
> 
> On Mon, Oct 3, 2016 at 10:36 AM, Stephan Mueller <smueller@chronox.de> 
wrote:
> > Am Montag, 3. Oktober 2016, 10:06:23 CEST schrieb Alex Cope:
> > 
> > Hi Alex,
> > 
> >> I'm currently working on implementing HEH encryption, and am in the
> >> process of switching from the blkcipher interface to the skcipher
> >> interface.  All the examples I have found that use skcipher are
> >> wrapping another mode of operation I.E. cts in cts(cbc(aes)) rather
> >> than being directly above the block cipher I.E. ctr in ctr(aes). Are
> >> there any existing examples of the latter type that I could use as a
> >> reference? If not, is there an estimate on when that work will be
> >> available?
> > 
> > The issue is that a blkcipher is a synchronous version of the skcipher.
> > So,
> > you could easily move from blkcipher to skcipher and just rename the
> > invoked API, provided you change the initialization to the following
> > which triggers a synchronous operation:
> > 
> > tfm = crypto_alloc_skcipher(kccavs_test->name, 0, CRYPTO_ALG_ASYNC);
> > 
> > Note, you can only use ciphers marked as blkcipher or cipher in
> > /proc/crypto with that.
> > 
> > If you want to use all symmetric cipher implementation, you must use the
> > async skcipher operation which is identical to the previous ablkcipher
> > API. An example is given in the crypto API documentation, such as http://
> > www.chronox.de/crypto-API/Code.html#id-1.8.2
> > 
> > Ciao
> > Stephan



Ciao
Stephan