kex_dh_compute_key
int kex_dh_compute_key(struct kex *, BIGNUM *, struct sshbuf *);
if ((r = kex_dh_compute_key(kex, dh_pub, buf)) != 0)
if ((r = kex_dh_compute_key(kex, dh_server_pub, shared_secret)) != 0)
if ((r = kex_dh_compute_key(kex, dh_client_pub, shared_secret)) != 0)