eay_dh_compute
extern int eay_dh_compute(vchar_t *, uint32_t, vchar_t *, vchar_t *,
eay_dh_compute(&p1, 2, pub1, priv1, pub2, &gxy1);
eay_dh_compute(&p2, 2, pub2, priv2, pub1, &gxy2);
if (eay_dh_compute(dh->prime, dh->gen1, pub, priv, pub_p, gxy) < 0) {