The First Key of Power is an artifact that Dunkelzahn's Will bequeathed to either Tir Tairngire or Tír na nÓg, with the condition that one of the nations must publicly disclose the complete personal histories of all of their high government officials. So far neither nation has attempted to fulfill the request to obtain the Key of Power.
The shape of the Key is unknown. However, it's power is to act as an additional member of a ritual spell casting when bound to the leader of the ritual.
The First Key of Power maybe an Earthdawn artifact; Keys to the Heart of Heroes.