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@xxxxxxxxxxxxx> --- 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..ea7b28b5e00e 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 + * 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 (!strcmp(curve->name, "nist_521")) { + 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 ee6886547fd1..22931f0c7295 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 (576 / 64) /* due to NIST P521 */ #define ECC_DIGITS_TO_BYTES_SHIFT 3 -- 2.43.0