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ecp_curves: Re-introduced mbedtls_ecp_fix_negative()

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This patch re-introduces `mbedtls_ecp_fix_negative` and
appropriately adjusts its' define guards.

Signed-off-by: Minos Galanakis <minos.galanakis@arm.com>
This commit is contained in:
Minos Galanakis 2023-03-22 11:28:15 +00:00
parent 4af90bbcda
commit 68d64a10b6
1 changed files with 33 additions and 0 deletions
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33
library/ecp_curves.c
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@ -5299,6 +5299,39 @@ int mbedtls_ecp_mod_p384_raw(mbedtls_mpi_uint *X, size_t X_limbs)
MBEDTLS_ECP_DP_SECP256R1_ENABLED ||
MBEDTLS_ECP_DP_SECP384R1_ENABLED */
#if defined(MBEDTLS_TEST_HOOKS) && defined(MBEDTLS_ECP_C)
MBEDTLS_STATIC_TESTABLE
void mbedtls_ecp_fix_negative(mbedtls_mpi *N, signed char c, size_t bits)
{
size_t i;
/* Set N := 2^bits - 1 - N. We know that 0 <= N < 2^bits, so
* set the absolute value to 0xfff...fff - N. There is no carry
* since we're subtracting from all-bits-one. */
for (i = 0; i <= bits / 8 / sizeof(mbedtls_mpi_uint); i++) {
N->p[i] = ~(mbedtls_mpi_uint) 0 - N->p[i];
}
/* Add 1, taking care of the carry. */
i = 0;
do {
++N->p[i];
} while (N->p[i++] == 0 && i <= bits / 8 / sizeof(mbedtls_mpi_uint));
/* Invert the sign.
* Now N = N0 - 2^bits where N0 is the initial value of N. */
N->s = -1;
/* Add |c| * 2^bits to the absolute value. Since c and N are
* negative, this adds c * 2^bits. */
mbedtls_mpi_uint msw = (mbedtls_mpi_uint) -c;
#if defined(MBEDTLS_HAVE_INT64)
if (bits == 224) {
msw <<= 32;
}
#endif
N->p[bits / 8 / sizeof(mbedtls_mpi_uint)] += msw;
}
#endif /* MBEDTLS_TEST_HOOKS & MBEDTLS_ECP_C */
#if defined(MBEDTLS_ECP_DP_SECP521R1_ENABLED)
/* Size of p521 in terms of mbedtls_mpi_uint */
#define P521_WIDTH (521 / 8 / sizeof(mbedtls_mpi_uint) + 1)