If I am using MBEDTLS_ECP_DP_SECP256R1 curve, then is it possible to used fixed (pre-calculated) value for the “mbedtls_ecp_point T; /!< pre-computed points for ecp_mul_comb() */”.
The calculaton process using long time on micro controller(msp430f6779) with low processing speed. So I like to hard-code the value on signature verification process. Does it work for all cases ?
typedef struct
{
mbedtls_ecp_group_id id; /*!< internal group identifier /
mbedtls_mpi P; /!< prime modulus of the base field /
mbedtls_mpi A; /!< 1. A in the equation, or 2. (A + 2) / 4 /
mbedtls_mpi B; /!< 1. B in the equation, or 2. unused /
mbedtls_ecp_point G; /!< generator of the (sub)group used /
mbedtls_mpi N; /!< 1. the order of G, or 2. unused /
size_t pbits; /!< number of bits in P /
size_t nbits; /!< number of bits in 1. P, or 2. private keys /
unsigned int h; /!< internal: 1 if the constants are static */
int (*modp)(mbedtls_mpi ); /!< function for fast reduction mod P */
int (*t_pre)(mbedtls_ecp_point *, void ); /!< unused */
int (*t_post)(mbedtls_ecp_point *, void ); /!< unused */
void t_data; /!< unused */
mbedtls_ecp_point T; /!< pre-computed points for ecp_mul_comb() /
size_t T_size; /!< number for pre-computed points */
}
mbedtls_ecp_group;