Re: [PATCH 4/4] crypto: lmk2/lmk3 cipher block modes

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On Mon, Dec 28, 2009 at 06:59:15PM +0000, Max Vozeler wrote:
> This is a compatible implementation of the block chaining
> modes used by the Loop-AES block device encryption system
> (http://loop-aes.sf.net/).
> 
> It implements two modes: lmk2 and lmk3. They correspond to
> the modes used in Loop-AES v2.x and Loop-AES v3.x and are
> intended to be full compatible.
> 
> Both modes operate on full 512 byte sectors. They use CBC
> with an IV derived from the sector number, the data and (for
> lmk3 only) an extra 128-bit IV seed.
> 
> Signed-off-by: Max Vozeler <max@xxxxxxxxxxxxx>
> Cc: Jari Ruusu <jariruusu@xxxxxxxxxxxxxxxxxxxxx>

So this is just CBC with a modified IV? If so it should not be
implemented as another mode.  Doing it as a mode means that you
will not benefit from any hardware implementations of CBC.

You should instead implement it as an IV generator.  Currently
they're done in dm-crypt.  But we could move them into crypto
at some point if there are multiple users in the kernel.

Cheers,
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