[dm-devel] [PATCH v3 1/6] crypto: essiv - create wrapper template for ESSIV generation

[Herbert Xu]

On Wed, Jun 19, 2019 at 06:04:17PM -0700, Eric Biggers wrote:
>
> > +#define ESSIV_IV_SIZE		sizeof(u64)	// IV size of the outer algo
> > +#define MAX_INNER_IV_SIZE	16		// max IV size of inner algo
> 
> Why does the outer algorithm declare a smaller IV size?  Shouldn't it just be
> the same as the inner algorithm's?

In general we allow outer algorithms to have distinct IV sizes
compared to the inner algorithm.  For example, rfc4106 has a
different IV size compared to gcm.

In this case, the outer IV size is the block number so that's
presumably why 64 bits is sufficient.  Do you forsee a case where
we need 128-bit block numbers?

Cheers,
-- 
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