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bignum: use CT modinv when N is odd

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Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
This commit is contained in:
Manuel Pégourié-Gonnard
2025-08-08 09:21:23 +02:00
parent 00076b4907
commit cdfd1c9c7d
1 changed files with 33 additions and 0 deletions
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33
library/bignum.c
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@@ -1968,6 +1968,35 @@ int mbedtls_mpi_random(mbedtls_mpi *X,
return mbedtls_mpi_core_random(X->p, min, N->p, X->n, f_rng, p_rng);
}
/*
* Modular inverse: X = A^-1 mod N with N odd (and A any range)
*/
static int mbedtls_mpi_inv_mod_odd(mbedtls_mpi *X,
const mbedtls_mpi *A,
const mbedtls_mpi *N)
{
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
mbedtls_mpi T, G;
mbedtls_mpi_init(&T);
mbedtls_mpi_init(&G);
MBEDTLS_MPI_CHK(mbedtls_mpi_mod_mpi(&T, A, N));
MBEDTLS_MPI_CHK(mbedtls_mpi_gcd_modinv_odd(&G, &T, &T, N));
if (mbedtls_mpi_cmp_int(&G, 1) != 0) {
ret = MBEDTLS_ERR_MPI_NOT_ACCEPTABLE;
goto cleanup;
}
MBEDTLS_MPI_CHK(mbedtls_mpi_copy(X, &T));
cleanup:
mbedtls_mpi_free(&T);
mbedtls_mpi_free(&G);
return ret;
}
/*
* Modular inverse: X = A^-1 mod N (HAC 14.61 / 14.64)
*/
@@ -1980,6 +2009,10 @@ int mbedtls_mpi_inv_mod(mbedtls_mpi *X, const mbedtls_mpi *A, const mbedtls_mpi
return MBEDTLS_ERR_MPI_BAD_INPUT_DATA;
}
if (mbedtls_mpi_get_bit(N, 0) == 1) {
return mbedtls_mpi_inv_mod_odd(X, A, N);
}
mbedtls_mpi_init(&TA); mbedtls_mpi_init(&TU); mbedtls_mpi_init(&U1); mbedtls_mpi_init(&U2);
mbedtls_mpi_init(&G); mbedtls_mpi_init(&TB); mbedtls_mpi_init(&TV);
mbedtls_mpi_init(&V1); mbedtls_mpi_init(&V2);