static int ecp_mul_comb()

in Simulation/RIoT/Core/RIoTCrypt/ecp.c [2080:2199]

• 85 lines of code
• 20 McCabe index (conditional complexity)

static int ecp_mul_comb( mbedtls_ecp_group *grp, mbedtls_ecp_point *R,
                         const mbedtls_mpi *m, const mbedtls_ecp_point *P,
                         int (*f_rng)(void *, unsigned char *, size_t),
                         void *p_rng,
                         mbedtls_ecp_restart_ctx *rs_ctx )
{
    int ret;
    unsigned char w, p_eq_g, i;
    size_t d;
    unsigned char T_size, T_ok;
    mbedtls_ecp_point *T;

    ECP_RS_ENTER( rsm );

    /* Is P the base point ? */
#if MBEDTLS_ECP_FIXED_POINT_OPTIM == 1
    p_eq_g = ( mbedtls_mpi_cmp_mpi( &P->Y, &grp->G.Y ) == 0 &&
               mbedtls_mpi_cmp_mpi( &P->X, &grp->G.X ) == 0 );
#else
    p_eq_g = 0;
#endif

    /* Pick window size and deduce related sizes */
    w = ecp_pick_window_size( grp, p_eq_g );
    T_size = 1U << ( w - 1 );
    d = ( grp->nbits + w - 1 ) / w;

    /* Pre-computed table: do we have it already for the base point? */
    if( p_eq_g && grp->T != NULL )
    {
        /* second pointer to the same table, will be deleted on exit */
        T = grp->T;
        T_ok = 1;
    }
    else
#if defined(MBEDTLS_ECP_RESTARTABLE)
    /* Pre-computed table: do we have one in progress? complete? */
    if( rs_ctx != NULL && rs_ctx->rsm != NULL && rs_ctx->rsm->T != NULL )
    {
        /* transfer ownership of T from rsm to local function */
        T = rs_ctx->rsm->T;
        rs_ctx->rsm->T = NULL;
        rs_ctx->rsm->T_size = 0;

        /* This effectively jumps to the call to mul_comb_after_precomp() */
        T_ok = rs_ctx->rsm->state >= ecp_rsm_comb_core;
    }
    else
#endif
    /* Allocate table if we didn't have any */
    {
        T = mbedtls_calloc( T_size, sizeof( mbedtls_ecp_point ) );
        if( T == NULL )
        {
            ret = MBEDTLS_ERR_ECP_ALLOC_FAILED;
            goto cleanup;
        }

        for( i = 0; i < T_size; i++ )
            mbedtls_ecp_point_init( &T[i] );

        T_ok = 0;
    }

    /* Compute table (or finish computing it) if not done already */
    if( !T_ok )
    {
        MBEDTLS_MPI_CHK( ecp_precompute_comb( grp, T, P, w, d, rs_ctx ) );

        if( p_eq_g )
        {
            /* almost transfer ownership of T to the group, but keep a copy of
             * the pointer to use for calling the next function more easily */
            grp->T = T;
            grp->T_size = T_size;
        }
    }

    /* Actual comb multiplication using precomputed points */
    MBEDTLS_MPI_CHK( ecp_mul_comb_after_precomp( grp, R, m,
                                                 T, T_size, w, d,
                                                 f_rng, p_rng, rs_ctx ) );

cleanup:

    /* does T belong to the group? */
    if( T == grp->T )
        T = NULL;

    /* does T belong to the restart context? */
#if defined(MBEDTLS_ECP_RESTARTABLE)
    if( rs_ctx != NULL && rs_ctx->rsm != NULL && ret == MBEDTLS_ERR_ECP_IN_PROGRESS && T != NULL )
    {
        /* transfer ownership of T from local function to rsm */
        rs_ctx->rsm->T_size = T_size;
        rs_ctx->rsm->T = T;
        T = NULL;
    }
#endif

    /* did T belong to us? then let's destroy it! */
    if( T != NULL )
    {
        for( i = 0; i < T_size; i++ )
            mbedtls_ecp_point_free( &T[i] );
        mbedtls_free( T );
    }

    /* don't free R while in progress in case R == P */
#if defined(MBEDTLS_ECP_RESTARTABLE)
    if( ret != MBEDTLS_ERR_ECP_IN_PROGRESS )
#endif
    /* prevent caller from using invalid value */
    if( ret != 0 )
        mbedtls_ecp_point_free( R );

    ECP_RS_LEAVE( rsm );

    return( ret );
}