Re: dm-crypt, new IV and standards

[Jean-Luc Cooke]

On Sat, Feb 21, 2004 at 11:48:21AM -0500, Jean-Luc Cooke wrote:
> > Please focus your recommendations on security, not backward compatibility
> > with something that is new to the kernel tree, broken and maintainerless.
 
> I'll start writing OMAC now.

FYI OMAC spec:
  http://crypt.cis.ibaraki.ac.jp/omac/omac.html

As you can see, there is a fixed output no matter how large the input it, the
output is always 128 bits.

So how will this fit into the cipher.c interface?

        case CRYPTO_TFM_MODE_CTR:
                ops->cit_encrypt = omac_compute;
                ops->cit_decrypt = nocrypt;
                ops->cit_encrypt_iv = nocrypt_iv;
                ops->cit_decrypt_iv = nocrypt_iv;
                break;


But now the user will have to call cit_encrypt(tfm, dst[0], src[i], nbytes);
Notice how dest will always have to be dst[0].  Unless we use the hash interface.

Thoughts?

static int omac_encrypt(struct crypto_tfm *tfm,
                       struct scatterlist *dst,
                       struct scatterlist *src,
                       unsigned int nbytes)
{
        return crypt(tfm, dst, src, nbytes,
                     tfm->__crt_alg->cra_cipher.cia_encrypt,
                     omac_process, 1, tfm->crt_cipher.cit_iv);
}

JLC - has CTR mode implemented and will post once he has OMAC done as well.

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