RE: [EXTERNAL] [PATCH v6 06/13] crypto: ecc - Implement vli_mmod_fast_521 for NIST p521

Bharat Bhushan
2024-03-18T05:48:14Z

> -----Original Message-----
> From: Stefan Berger <stefanb@linux.vnet.ibm.com>
> Sent: Wednesday, March 13, 2024 12:06 AM
> To: keyrings@vger.kernel.org; linux-crypto@vger.kernel.org;
> herbert@gondor.apana.org.au; davem@davemloft.net
> Cc: linux-kernel@vger.kernel.org; saulo.alessandre@tse.jus.br;
> lukas@wunner.de; Bharat Bhushan <bbhushan2@marvell.com>;
> jarkko@kernel.org; Stefan Berger <stefanb@linux.ibm.com>
> Subject: [EXTERNAL] [PATCH v6 06/13] crypto: ecc - Implement
> vli_mmod_fast_521 for NIST p521
>
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>
> ----------------------------------------------------------------------
> From: Stefan Berger <stefanb@linux.ibm.com>
>
> Implement vli_mmod_fast_521 following the description for how to calculate
> the modulus for NIST P521 in the NIST publication "Recommendations for
> Discrete Logarithm-Based Cryptography: Elliptic Curve Domain Parameters"
> section G.1.4.
>
> NIST p521 requires 9 64bit digits, so increase the ECC_MAX_DIGITS so that
> arrays fit the larger numbers.
>
> Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
> ---
> crypto/ecc.c | 25 +++++++++++++++++++++++++
> include/crypto/internal/ecc.h | 3 ++-
> 2 files changed, 27 insertions(+), 1 deletion(-)
>
> diff --git a/crypto/ecc.c b/crypto/ecc.c index 415a2f4e7291..99d41887c005
> 100644
> --- a/crypto/ecc.c
> +++ b/crypto/ecc.c
> @@ -902,6 +902,28 @@ static void vli_mmod_fast_384(u64 *result, const
> u64 *product, #undef AND64H #undef AND64L
>
> +/*
> + * Computes result = product % curve_prime
> + * from "Recommendations for Discrete Logarithm-Based Cryptography:
> + * Elliptic Curve Domain Parameters" section G.1.4
> + */
> +static void vli_mmod_fast_521(u64 *result, const u64 *product,
> + const u64 *curve_prime, u64 *tmp) {
> + const unsigned int ndigits = ECC_CURVE_NIST_P521_DIGITS;
> + size_t i;
> +
> + /* Initialize result with lowest 521 bits from product */
> + vli_set(result, product, ndigits);
> + result[8] &= 0x1ff;
> +
> + for (i = 0; i < ndigits; i++)
> + tmp[i] = (product[8 + i] >> 9) | (product[9 + i] << 55);
> + tmp[8] &= 0x1ff;

Can we get away from this hardcoding, like 9, 55, 0x1ff etc.
Or at least add comment about these.

> +
> + vli_mod_add(result, result, tmp, curve_prime, ndigits); }
> +
> /* Computes result = product % curve_prime for different curve_primes.
> *
> * Note that curve_primes are distinguished just by heuristic check and @@ -
> 941,6 +963,9 @@ static bool vli_mmod_fast(u64 *result, u64 *product,
> case ECC_CURVE_NIST_P384_DIGITS:
> vli_mmod_fast_384(result, product, curve_prime, tmp);
> break;
> + case ECC_CURVE_NIST_P521_DIGITS:
> + vli_mmod_fast_521(result, product, curve_prime, tmp);
> + break;
> default:
> pr_err_ratelimited("ecc: unsupported digits size!\n");
> return false;
> diff --git a/include/crypto/internal/ecc.h b/include/crypto/internal/ecc.h index
> ab722a8986b7..4e2f5f938e91 100644
> --- a/include/crypto/internal/ecc.h
> +++ b/include/crypto/internal/ecc.h
> @@ -33,7 +33,8 @@
> #define ECC_CURVE_NIST_P192_DIGITS 3
> #define ECC_CURVE_NIST_P256_DIGITS 4
> #define ECC_CURVE_NIST_P384_DIGITS 6
> -#define ECC_MAX_DIGITS (512 / 64) /* due to ecrdsa */
> +#define ECC_CURVE_NIST_P521_DIGITS 9

Maybe these can be defined as:
#define ECC_CURVE_NIST_P521_DIGITS (DIV_ROUND_UP(521, 64) /* NIST P521 */)

> +#define ECC_MAX_DIGITS DIV_ROUND_UP(521, 64) /* NIST P521 */

/* NIST_P521 is max digits */
#define ECC_MAX_DIGITS ECC_CURVE_ _DIGITS

Thanks
-Bharat

>
> #define ECC_DIGITS_TO_BYTES_SHIFT 3
>
> --
> 2.43.0