[dm-devel] [PATCH v8 1/7] crypto: essiv - create wrapper template for ESSIV generation

[Herbert Xu]

Ard Biesheuvel <ard.biesheuvel at linaro.org> wrote:
>
> + * The typical use of this template is to instantiate the skcipher
> + * 'essiv(cbc(aes),aes,sha256)', which is the only instantiation used by
> + * fscrypt, and the most relevant one for dm-crypt. However, dm-crypt
> + * also permits ESSIV to be used in combination with the authenc template,
> + * e.g., 'essiv(authenc(hmac(sha256),cbc(aes)),aes,sha256)', in which case
> + * we need to instantiate an aead that accepts the same special key format
> + * as the authenc template, and deals with the way the encrypted IV is
> + * embedded into the AAD area of the aead request. This means the AEAD
> + * flavor produced by this template is tightly coupled to the way dm-crypt
> + * happens to use it.

IIRC only authenc is allowed in dm-crypt currently in conjunction
with ESSIV.  Does it ever allow a different hash algorithm in
authenc compared to the one used for ESSIV? IOW given

	essiv(authenc(hmac(X),cbc(Y)),Z,U)

is it currently possible for X != U or Y != Z? If not then let's
just make the algorithm name be essiv(Y,X).

Because this is legacy stuff, I don't want it to support any more
than what is currently being supported by dm-crypt.

Similary for the skcipher case, given

	essiv(cbc(X),Y,Z)

is it ever possible for X != Y? If not then we should just make the
algorithm name essiv(X,Z).

Thanks,
-- 
Email: Herbert Xu <herbert at gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt