Re: [PATCH v10 3/9] crypto: Add math to support fast NIST P384

[Stefan Berger]

On 3/6/21 2:25 PM, Vitaly Chikunov wrote:
> Stefan,
>
> On Thu, Mar 04, 2021 at 07:51:57PM -0500, Stefan Berger wrote:
> > From: Saulo Alessandre <saulo.alessandre@xxxxxxxxxx>
> >
> > * crypto/ecc.c
> >    - add vli_mmod_fast_384
> >    - change some routines to pass ecc_curve forward until vli_mmod_fast
> >
> > * crypto/ecc.h
> >    - add ECC_CURVE_NIST_P384_DIGITS
> >    - change ECC_MAX_DIGITS to P384 size
> >
> > Signed-off-by: Saulo Alessandre <saulo.alessandre@xxxxxxxxxx>
> > Tested-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
> > ---
> >   crypto/ecc.c | 266 +++++++++++++++++++++++++++++++++++++--------------
> >   crypto/ecc.h |   3 +-
> >   2 files changed, 194 insertions(+), 75 deletions(-)
> >
> > diff --git a/crypto/ecc.c b/crypto/ecc.c
> > index f6cef5a7942d..c125576cda6b 100644
> > --- a/crypto/ecc.c
> > +++ b/crypto/ecc.c
> > @@ -778,18 +778,133 @@ static void vli_mmod_fast_256(u64 *result, const u64 *product,
> >   ...
> >   /* Computes result = product % curve_prime for different curve_primes.
> >    *
> >    * Note that curve_primes are distinguished just by heuristic check and
> >    * not by complete conformance check.
> >    */
> >   static bool vli_mmod_fast(u64 *result, u64 *product,
> > -			  const u64 *curve_prime, unsigned int ndigits)
> > +			  const struct ecc_curve *curve)
> >   {
> >   	u64 tmp[2 * ECC_MAX_DIGITS];
> > +	const u64 *curve_prime = curve->p;
> > +	const unsigned int ndigits = curve->g.ndigits;
> >   
> > -	/* Currently, both NIST primes have -1 in lowest qword. */
> > -	if (curve_prime[0] != -1ull) {
> > +	/* Currently, all NIST have name nist_.* */
> > +	if (strncmp(curve->name, "nist_", 5) != 0) {
> I am not sure, but maybe this strncmp should not be optimized somehow,
> since vli_mmod_fast could be called quite frequently. Perhaps by integer
> algo id or even callback?

Should be optimized or should not be? You seem to say both.

The code code here is shared with ecrdsa. The comparison won't go beyond 
a single letter considering the naming of the curves define here:

"cp256a": 
https://elixir.bootlin.com/linux/v5.11.3/source/crypto/ecrdsa_defs.h#L49

"cp256b": 
https://elixir.bootlin.com/linux/v5.11.3/source/crypto/ecrdsa_defs.h#L82

"cp256c": 
https://elixir.bootlin.com/linux/v5.11.3/source/crypto/ecrdsa_defs.h#L119

"tc512a": 
https://elixir.bootlin.com/linux/v5.11.3/source/crypto/ecrdsa_defs.h#L168

and here:

"nist_192": 
https://elixir.bootlin.com/linux/v5.11.3/source/crypto/ecc_curve_defs.h#L18

"nist_256": 
https://elixir.bootlin.com/linux/v5.11.3/source/crypto/ecc_curve_defs.h#L45


All the ecrdsa curves were previously evaluating 'curve_prime[0] != 
-1ull', so it doesn't change anything.

  Stefan