Ring of Namira

[cmac]

In one of my meandering ventures through the TES:CS, I stumbled upon the excellent model of the Ring of Namira. I looked up it's function on the Internet, and it was this:

"While the ring is being worn, any damage the bearer takes is suffered by the attacker as well. Spells and missile attacks are ignored. How much damage the attacker suffers depends upon his nature. Animals and Spriggans take no damage, being creatures of nature. Daedric beings only take half the damage they do, being supernatural creatures. Humanoids and monsters take full damage. Undead take twice the damage they dole out, because they are wholly unnatural creatures."

I have some trouble categorizing this into a spell effect, and would reatly appreciate some help in scripting the effects for this incredible ring. I can script basic functions in the 'Set, but this is beyond me. Once again, any help would be supremly appreciated, and I would have course give full credit to the script-writer.