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SubjectRe: [PATCH/proposal] dm-crypt: add digest-based iv generation mode
On Tue, 24 Feb 2004, Jean-Luc Cooke wrote:

> On Tue, Feb 24, 2004 at 05:17:12PM -0500, James Morris wrote:
> > On Tue, 24 Feb 2004, Jean-Luc Cooke wrote:
> >
> > > The two patches are:
> > > - http://jlcooke.ca/lkml/ctr_and_omac.patch
> > > (added ctr to cipher.c and omac.c)
> > > Using the init/update/final interface.
> > > - http://jlcooke.ca/lkml/ctr_and_omac2.patch
> > > (added ctr to cipher.c and integrated OMAC into all
> > > existing modes of operation. If cipher_tfm.cit_omac!=NULL, OMAC is stored
> > > into cipher_tfm.cit_omac)
> >
> > Looks good so far, although the duplicated scatterwalk code needs to be
> > put into a separate file (e.g. scatterwalk.c).
>
> OK. So which patch do you want? :) The omac.c with scatterwalk, or the
> cipher.c with omac performed in-place when needed?

I think the latter is preferrable. OMAC should probably be a config
option as well.

>
> > > ps. Will crypto_cipher_encrypt/crypto_cipher_decrypt *always* be called in
> > > onesies? I need to perform come final() code on the OMAC before it's
> > > ready to pass test vectors - how do I know when we're done?
> >
> > I don't understand what you mean here.
>
> finish_omac() needs to be called once all data is processed. How do I know
> for sure the caller is done with this cipher context instance?
>
> For example:
> loop {
> /* get more data into sgin */
> crypto_cipher_encrypt(tfm, sgout, sgin, len);
> /* send our data out of sgout */
> }
> /* get the 128bit OMAC and send it since we're done with all our encryption */
>
> And decryption:
> loop {
> /* get more data into sgin */
> crypto_cipher_decrypt(tfm, sgout, sgin, len);
> /* send our data out of sgout */
> }
> /* get the 128bit OMAC and compare it with transmitted OMAC since we're done
> with all our decryption */
>
> There is no explicit/implicit "crypto_cipher_encrypt_final()" to inform the
> API to finalise the OMAC.

You could add something like crypto_cipher_omac_final(), to be used by the
calling code once it needs the OMAC value, which then calls
crypto_cipher_get_omac().


- James
--
James Morris
<jmorris@redhat.com>


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