1 Reply by hdan

(4 replies, posted in wolfCrypt)

Hi Chris,

I'm trying to implement "Elliptic Curve Qu-Vanstone Implicit Certificate Scheme" based on http://www.secg.org/sec4-1.0.pdf.

I tried to modify my function like this:

int wc_ecc_add2point(ecc_point* P, ecc_point* Q, ecc_point* R, mp_int* modulus){
    mp_digit mp;
    mp_int mu;
    ecc_point *tP, *tQ;
    int err;
    /* init montgomery reduction */
    if ((err = mp_montgomery_setup(modulus, &mp)) != MP_OKAY) {
      return err;
    }
    if ((err = mp_init(&mu)) != MP_OKAY) {
        return err;
    }
    if ((err = mp_montgomery_calc_normalization(&mu, modulus)) != MP_OKAY) {
        mp_clear(&mu);
        return err;
    }
    tP = wc_ecc_new_point();
    tQ = wc_ecc_new_point();
    if (err == MP_OKAY) {
           if (mp_cmp_d(&mu, 1) == MP_EQ) {
               err = mp_copy(P->x, tP->x);
               if (err == MP_OKAY)
                   err = mp_copy(P->y, tP->y);
               if (err == MP_OKAY)
                   err = mp_copy(P->z, tP->z);
           } else {
               err = mp_mulmod(P->x, &mu, modulus, tP->x);
               if (err == MP_OKAY)
                   err = mp_mulmod(P->y, &mu, modulus, tP->y);
               if (err == MP_OKAY)
                   err = mp_mulmod(P->z, &mu, modulus, tP->z);
           }
       }
    if (err == MP_OKAY) {
           if (mp_cmp_d(&mu, 1) == MP_EQ) {
               err = mp_copy(Q->x, tQ->x);
               if (err == MP_OKAY)
                   err = mp_copy(Q->y, tQ->y);
               if (err == MP_OKAY)
                   err = mp_copy(Q->z, tQ->z);
           } else {
               err = mp_mulmod(Q->x, &mu, modulus, tQ->x);
               if (err == MP_OKAY)
                   err = mp_mulmod(Q->y, &mu, modulus, tQ->y);
               if (err == MP_OKAY)
                   err = mp_mulmod(Q->z, &mu, modulus, tQ->z);
           }
       }
    if((err = ecc_projective_add_point(tP, tQ, R, modulus, &mp))!=MP_OKAY){
        return err;
    }

    if((err = ecc_map(R, modulus, &mp))!=MP_OKAY) {
        return err;
    }
    return MP_OKAY;
}

To expose wc_ecc_add2point as a part of public API, I added the prototype of the function on ecc.h like this: 

WOLFSSL_API
int wc_ecc_add2point(ecc_point* P, ecc_point* Q, ecc_point* R, mp_int* modulus);

And then I called it in an other function in ssl.c:

    ecc_point* base, *eccD;
    const ecc_set_type* dp =  &ecc_sets[curve_index];
        int err;
    base = wc_ecc_new_point();

    /*Get domain curve parameters*/
        err = mp_read_radix(&prime, (char *) dp->prime, 16);
    if (err == MP_OKAY)
        err = mp_read_radix(&order, (char *) dp->order, 16);
    if (err == MP_OKAY)
        err = mp_read_radix(base->x, (char *) dp->Gx, 16);
    if (err == MP_OKAY)
        err = mp_read_radix(base->y, (char *) dp->Gy, 16);
    if (err == MP_OKAY)
        mp_set(base->z, 1);
    eccD = wc_ecc_new_point();
    err = wc_ecc_add2point(base, base, eccD, &prime);

And the result was seem 'OK'. eccD point was actually double base point. But I still don't know whether my implement (the way I used ecc_projective_add_point function) is correct or not? And the way I use to expose the function as a part of public API of wolfSSL is right?

Can you give me advice?

Thank You,

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2 Reply by hdan

(4 replies, posted in wolfCrypt)

Hi Chrisc,

Thank you for your answer!
I'm try to use ecc_projective_add_point() function, but the result isn't as expecting. It seems like I used it incorrectly. The following is the function which I write to add two ecc points:

int wc_ecc_add2point(ecc_point* P, ecc_point* Q, ecc_point* R, mp_int* modulus){
    mp_digit mp;
    int err;
    if ((err = mp_montgomery_setup(modulus, &mp)) != MP_OKAY) {
      return err;
    }
    if((err = ecc_projective_add_point(P, Q, R, modulus, &mp))!=MP_OKAY){
        return err;
    }
    if((err = ecc_map(R, modulus, &mp))!=MP_OKAY) {
        return err;
    }
    return MP_OKAY;
}

Is it ok if I use P and Q in affine coordinate format to put on ecc_projective_add_point() function?
Please help me how to use this function. 
Thank You!

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3 Topic by hdan

(4 replies, posted in wolfCrypt)

Hi,

Do wolfssl support addition two ecc points?

Thank You!

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