There is not a key. At the entrance where the portal is located, there are platforms going up the side of the wall where the gate is. You have to work your way to a platform with a lever to open the gate.
no keys you have to jump on platforms and stuff to find levers to open the doors
Where i come from ascesion to a higher rank is a simple assasination those who are Ranked Highest watch their Front their deaths come from thier back and they die naturally because a dagger in the back naturallyu ends their life.