1- Since backbiting is one of those sins that you have to ask forgivness for from both Allah and from the person you backbite, is it sufficient to ask the person to forgive you by saying «forgive me if I ever spoke bad about you, and so indicating that maybe I have or maybe I havent, or is it mandatory to tell him what I have said, and to whom I said it?

2- If I have listened to backbiting, do I also then have to ask for forgivness from the person who was backbitten, if I willingly listened to the gossip (even if I was not the one to speak), or is it sufficient to ask Allah for forgiveness.
(Also if I have to ask the person, do I tell him I spoke ill of him, or that I listened to it, and do I need to say who actually spoke ill of him if he was to ask?)