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    SubjectRE: [EXTERNAL] [PATCH v6 06/13] crypto: ecc - Implement vli_mmod_fast_521 for NIST p521
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    > -----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
    >
    > Prioritize security for external emails: Confirm sender and content safety
    > before clicking links or opening attachments
    >
    > ----------------------------------------------------------------------
    > 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


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