Help with fire thorns chestplate!

So I am currently trying to make a chestplate that is "fire enhanced". My idea is that when a player wears the chestplate, every entity(player/entity) gets turned on fire, and the person that wears it gets fire resistance. The thing is that I am not sure what block I need to use to talk refer to the attacker. At first, I thought source entity could work, but it seems it does not. Can someone help me please? Here is a photo of my code: https://imgur.com/a/LMWfYKl

If anyone can help me, I would appreciate it very very much! Thanks!