On 3/7/24 14:11, Jarkko Sakkinen wrote:
> On Thu Mar 7, 2024 at 12:22 AM EET, Stefan Berger wrote:
>> 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>
>> Tested-by: Lukas Wunner <lukas@wunner.de>
>> ---
>> crypto/ecc.c | 31 +++++++++++++++++++++++++++++++
>> include/crypto/internal/ecc.h | 2 +-
>> 2 files changed, 32 insertions(+), 1 deletion(-)
>>
>> diff --git a/crypto/ecc.c b/crypto/ecc.c
>> index f53fb4d6af99..373660e7b19d 100644
>> --- a/crypto/ecc.c
>> +++ b/crypto/ecc.c
>> @@ -902,6 +902,31 @@ static void vli_mmod_fast_384(u64 *result, const u64 *product,
>> #undef AND64H
>> #undef AND64L
>>
>> +/* Computes result = product % curve_prime
>
> Missing empty comment line:
>
> /*
> *
>
>> + * from "Recommendations for Discrete Logarithm-Based Cryptography:
>> + * Elliptic Curve Domain Parameters" G.1.4
>> + */
>> +static void vli_mmod_fast_521(u64 *result, const u64 *product,
>> + const u64 *curve_prime, u64 *tmp)
>> +{
>> + const unsigned int ndigits = 9;
>> + size_t i;
>> +
>> + for (i = 0; i < ndigits; i++)
>> + tmp[i] = product[i];
>> + tmp[8] &= 0x1ff;
>> +
>> + vli_set(result, tmp, ndigits);
>> +
>> +
>> + for (i = 0; i < ndigits; i++)
>> + tmp[i] = (product[8 + i] >> 9) | (product[9 + i] << 55);
>> + tmp[8] &= 0x1ff;
>> +
>> + 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 +966,12 @@ static bool vli_mmod_fast(u64 *result, u64 *product,
>> case 6:
>> vli_mmod_fast_384(result, product, curve_prime, tmp);
>> break;
>> + case 9:
>> + if (curve->nbits == 521) {
>
> Missing inline comment about the branching decision, and has a magic
> number.
Ok, will add comment to this and 6/12.
>
>> + vli_mmod_fast_521(result, product, curve_prime, tmp);
>> + break;
>> + }
>> + fallthrough;
>> 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 4a556b41873e..de17bcdeb53a 100644
>> --- a/include/crypto/internal/ecc.h
>> +++ b/include/crypto/internal/ecc.h
>> @@ -33,7 +33,7 @@
>> #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_MAX_DIGITS DIV_ROUND_UP(521, 64) /* NIST P521 */
>>
>> #define ECC_DIGITS_TO_BYTES_SHIFT 3
>>
>
> BR, Jarkko