/* Elliptic curve scalar-point multiplication. Computes R(x, y) = k * P(x, * y). If x, y = NULL, then P is assumed to be the generator (base point) * of the group of points on the elliptic curve. Input and output values * are assumed to be NOT field-encoded. */ mp_err ECPoint_mul(const ECGroup *group, const mp_int *k, const mp_int *px, const mp_int *py, mp_int *rx, mp_int *ry) { mp_err res = MP_OKAY; mp_int kt; ARGCHK((k != NULL) && (group != NULL), MP_BADARG); MP_DIGITS(&kt) = 0; /* want scalar to be less than or equal to group order */ if (mp_cmp(k, &group->order) > 0) { MP_CHECKOK(mp_init(&kt, FLAG(k))); MP_CHECKOK(mp_mod(k, &group->order, &kt)); } else { MP_SIGN(&kt) = MP_ZPOS; MP_USED(&kt) = MP_USED(k); MP_ALLOC(&kt) = MP_ALLOC(k); MP_DIGITS(&kt) = MP_DIGITS(k); } if ((px == NULL) || (py == NULL)) { if (group->base_point_mul) { MP_CHECKOK(group->base_point_mul(&kt, rx, ry, group)); } else { MP_CHECKOK(group-> point_mul(&kt, &group->genx, &group->geny, rx, ry, group)); } } else { if (group->meth->field_enc) { MP_CHECKOK(group->meth->field_enc(px, rx, group->meth)); MP_CHECKOK(group->meth->field_enc(py, ry, group->meth)); MP_CHECKOK(group->point_mul(&kt, rx, ry, rx, ry, group)); } else { MP_CHECKOK(group->point_mul(&kt, px, py, rx, ry, group)); } } if (group->meth->field_dec) { MP_CHECKOK(group->meth->field_dec(rx, rx, group->meth)); MP_CHECKOK(group->meth->field_dec(ry, ry, group->meth)); } CLEANUP: if (MP_DIGITS(&kt) != MP_DIGITS(k)) { mp_clear(&kt); } return res; }
void mp_int_random(mp_int z, int prec) { int i; if(prec > MP_ALLOC(z)) prec = MP_ALLOC(z); for(i = 0; i < prec; ++i) { mp_digit d = 0; int j; for(j = 0; j < sizeof(d); ++j) d = (d << CHAR_BIT) | (rand() & UCHAR_MAX); z->digits[i] = d; } MP_USED(z) = prec; }