Re: [dpdk-stable] [dpdk-dev] [PATCH] cryptodev: fix SHA-1 digest enum comment

["Trahe, Fiona" <fiona.trahe@intel.com>]

Hi Adam, Anoob,


> > > >
> > > > > -----Original Message-----
> > > > > From: dev <dev-bounces@dpdk.org> On Behalf Of Adam Dybkowski
> > > > > Sent: Monday, May 18, 2020 7:54 PM
> > > > > To: dev@dpdk.org; fiona.trahe@intel.com; akhil.goyal@nxp.com
> > > > > Cc: Adam Dybkowski <adamx.dybkowski@intel.com>; stable@dpdk.org
> > > > > Subject: [dpdk-dev] [PATCH] cryptodev: fix SHA-1 digest enum
> > > > > comment
> > > > >
> > > > > This patch fixes improper SHA-1 digest size in the enum comment.
> > > > >
> > > > > Fixes: 1bd407fac80b ("cryptodev: extract symmetric operations")
> > > > > Cc: stable@dpdk.org
> > > > >
> > > > > Signed-off-by: Adam Dybkowski <adamx.dybkowski@intel.com>
> > > > > ---
> > > > >  lib/librte_cryptodev/rte_crypto_sym.h | 4 ++--
> > > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > > >
> > > > > diff --git a/lib/librte_cryptodev/rte_crypto_sym.h
> > > > > b/lib/librte_cryptodev/rte_crypto_sym.h
> > > > > index d9585ecd6..9cea4e5f0 100644
> > > > > --- a/lib/librte_cryptodev/rte_crypto_sym.h
> > > > > +++ b/lib/librte_cryptodev/rte_crypto_sym.h
> > > > > @@ -269,9 +269,9 @@ enum rte_crypto_auth_algorithm {
> > > > >  	/**< HMAC using MD5 algorithm */
> > > > >
> > > > >  	RTE_CRYPTO_AUTH_SHA1,
> > > > > -	/**< 128 bit SHA algorithm. */
> > > > > +	/**< 160 bit SHA algorithm. */
> > > > >  	RTE_CRYPTO_AUTH_SHA1_HMAC,
> > > > > -	/**< HMAC using 128 bit SHA algorithm. */
> > > > > +	/**< HMAC using 160 bit SHA algorithm. */
> > > >
> > > > [Anoob] This raises one interesting question. Is HMAC-SHA-1-96
> > > > (https://urldefense.proofpoint.com/v2/url?u=https-3A__tools.ietf.org
> > > > _h
> > > >
> > >
> > tml_rfc2404&d=DwIFAg&c=nKjWec2b6R0mOyPaz7xtfQ&r=jPfB8rwwviRSxyL
> > Ws2
> > > n6B-
> > >
> > WYLn1v9SyTMrT5EQqh2TU&m=pgqB2BfFosCF_7l1SdoodgXcipf7G1ofht68ZK
> > Mt
> > > oW0&s=hxzUN2QfRJGaR7NQ7VKGm5oQvOZez6Z70mqOyg7gKTY&e= )
> > treated as a
> > > separate algorithm or is it a digest size variant of
> > > RTE_CRYPTO_AUTH_SHA1_HMAC? I assume the later.
> > >
> > > [Adam] DPDK doesn't have separate enums for such variations. According
> > > to RFC 2104, chapter "5. Truncated output", the calculation of
> > > HMAC-SHA-1-96 is done using ordinary HMAC-SHA-1, but the calculation
> > > result is then truncated to 96 bits, or any other digest size provided in auth
> > xform.
> >
> > [Anoob] So it is allowed to support digest sizes 12 & 20, right? Can you
> > update the above comment in that case?
> 
> [Adam] This depends on a particular PMD and its capabilities so we cannot write here in this public
> header file. For example, have a look in the capabilities structure of QAT PMD:
> 
> 	{	/* SHA1 */						\
> 		.op = RTE_CRYPTO_OP_TYPE_SYMMETRIC,			\
> 		{.sym = {						\
> 			.xform_type = RTE_CRYPTO_SYM_XFORM_AUTH,	\
> 			{.auth = {					\
> 				.algo = RTE_CRYPTO_AUTH_SHA1,		\
> 				.block_size = 64,			\
> 				.key_size = {				\
> 					.min = 0,			\
> 					.max = 0,			\
> 					.increment = 0			\
> 				},					\
> 				.digest_size = {			\
> 					.min = 1,			\
> 					.max = 20,			\
> 					.increment = 1			\
> 				},					\
> 				.iv_size = { 0 }			\
> 			}, }						\
> 		}, }							\
> 	},								\
> 
> It shows QAT PMD is able to truncate the output digest to any size from 1 to 20 bytes (160 bits).
> 
> This can be different in other PMDs, for example OpenSSL and CCP PMDs allow only 20-byte digests
> here while Marvell MVSAM allows 12-20 bytes.
> 
> Adam
[Fiona] True. But as 96 bits is a standard variant described in the spec, how about adding

/**< HMAC using 160 bit SHA algorithm. 
HMAC-SHA-1-96 can be generated by setting digest_size to 12 */

This doesn't imply that all PMDs must support that - same as for any other feature, the capabilities can vary.