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ecp_curves: Refactored mbedtls_ecp_mod_p255.

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This patch introduces following methods, as implemented in the
design prototype, and updates them to utilise the _core methods
available for multiplication and addition.
* `mbedtls_ecp_mod_p255()`
* `mbedtls_ecp_mod_p255_raw()`

An entry has been exposed in the `ecp_invasive.h` header
to facilitate testing.

Signed-off-by: Minos Galanakis <minos.galanakis@arm.com>
This commit is contained in:
Minos Galanakis 2023-05-10 15:46:47 +01:00
parent 50729eac74
commit d0292c2aca
2 changed files with 44 additions and 14 deletions
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51
library/ecp_curves.c
View File

@ -4604,6 +4604,8 @@ int mbedtls_ecp_mod_p521_raw(mbedtls_mpi_uint *N_p, size_t N_n);
/* Additional forward declarations */
#if defined(MBEDTLS_ECP_DP_CURVE25519_ENABLED)
static int ecp_mod_p255(mbedtls_mpi *);
MBEDTLS_STATIC_TESTABLE
int mbedtls_ecp_mod_p255_raw(mbedtls_mpi_uint *X, size_t X_limbs);
#endif
#if defined(MBEDTLS_ECP_DP_CURVE448_ENABLED)
static int ecp_mod_p448(mbedtls_mpi *);
@ -5417,26 +5419,47 @@ int mbedtls_ecp_mod_p521_raw(mbedtls_mpi_uint *X, size_t X_limbs)
*/
static int ecp_mod_p255(mbedtls_mpi *N)
{
mbedtls_mpi_uint Mp[P255_WIDTH];
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
size_t expected_width = 2 * ((256 + biL - 1) / biL);
MBEDTLS_MPI_CHK(mbedtls_mpi_grow(N, expected_width));
ret = mbedtls_ecp_mod_p255_raw(N->p, expected_width);
cleanup:
return ret;
}
/* Helper references for top part of N */
mbedtls_mpi_uint * const NT_p = N->p + P255_WIDTH;
const size_t NT_n = N->n - P255_WIDTH;
if (N->n <= P255_WIDTH) {
MBEDTLS_STATIC_TESTABLE
int mbedtls_ecp_mod_p255_raw(mbedtls_mpi_uint *X, size_t X_Limbs)
{
mbedtls_mpi_uint carry[P255_WIDTH];
memset(carry, 0, sizeof(mbedtls_mpi_uint) * P255_WIDTH);
if (X_Limbs > 2*P255_WIDTH) {
X_Limbs = 2*P255_WIDTH;
} else if (X_Limbs < P255_WIDTH) {
return 0;
}
if (NT_n > P255_WIDTH) {
return MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
/* Step 1: Reduction to P255_WIDTH limbs */
if (X_Limbs > P255_WIDTH) {
/* Helper references for top part of N */
mbedtls_mpi_uint * const NT_p = X + P255_WIDTH;
const size_t NT_n = X_Limbs - P255_WIDTH;
/* N = A0 + 38 * A1, capture carry out */
carry[0] = mbedtls_mpi_core_mla(X, P255_WIDTH, NT_p, NT_n, 38);
/* Clear top part */
memset(NT_p, 0, sizeof(mbedtls_mpi_uint) * NT_n);
}
/* Split N as N + 2^256 M */
memcpy(Mp, NT_p, sizeof(mbedtls_mpi_uint) * NT_n);
memset(NT_p, 0, sizeof(mbedtls_mpi_uint) * NT_n);
/* Step 2: Reduce to <p
* Split as A0 + 2^255*c, with c a scalar, and compute A0 + 19*c */
carry[0] <<= 1;
carry[0] += (X[P255_WIDTH-1] >> (biL - 1));
carry[0] *= 19;
/* N = A0 + 38 * A1 */
mbedtls_mpi_core_mla(N->p, P255_WIDTH + 1,
Mp, NT_n,
38);
/* Clear top bit */
X[P255_WIDTH-1] <<= 1; X[P255_WIDTH-1] >>= 1;
(void) mbedtls_mpi_core_add(X, X, &carry[0], P255_WIDTH);
return 0;
}

7
library/ecp_invasive.h
View File

@ -241,6 +241,13 @@ int mbedtls_ecp_mod_p256k1_raw(mbedtls_mpi_uint *X, size_t X_limbs);
#endif /* MBEDTLS_ECP_DP_SECP256K1_ENABLED */
#if defined(MBEDTLS_ECP_DP_CURVE25519_ENABLED)
MBEDTLS_STATIC_TESTABLE
int mbedtls_ecp_mod_p255_raw(mbedtls_mpi_uint *X, size_t X_limbs);
#endif /* MBEDTLS_ECP_DP_CURVE25519_ENABLED */
#if defined(MBEDTLS_ECP_DP_CURVE448_ENABLED)
MBEDTLS_STATIC_TESTABLE