With signing server level of interaction is the thing that really matters. I would probably say that if you implemented algo doing the signing operation it migh

With signing server level of interaction is the thing that really matters. I would probably say that if you implemented algo doing the signing operation it might be questionable. But if you implemented the key storage fully yourself, it is even more questionable. Or design your HSM module, or just write the keys in plaintext or minimally protected on the disk... Also who designed and implemented checking the appended blob? Also crypto...