_dsa_sign_encode
if (_dsa_sign_encode(dsa, NULL, 0, &off) < 0)
if (_dsa_sign_encode(dsa, ptr, len, &off) < 0)
int _dsa_sign_encode(struct iked_dsa *, uint8_t *, size_t, size_t *);
if (_dsa_sign_encode(dsa, NULL, 0, NULL) < 0)