Ethereum Prison Key

Ethereum Prison Keys are keys used to open an Ethereum Prison.

Prerequisites
For the Ethereum Prison Keys to drop or allow one to roll on them within a party, one has to be honored with the Consortium and has to have completed the quest A Mission of Mercy.

If those prerequisites are not met the Ethereum Prison Key will not drop nor can one roll on them when they drop while within a party.

Source
Once the prerequisites are met, the Ethereum Prison Key drops off:
 * Ethereum mobs in the Arcatraz
 * Ethereal mobs in the Mana-Tombs
 * Ethereum mobs around Manaforge Ultris
 * Zaxxis mobs in and around The Heap
 * Bash'ir mobs in Bash'ir Landing

Note that the Ethereum Jailor around Manaforge Ultris in particular has a 100% drop rate of the Ethereum Prison Key.

As of Patch 2.3 a Ethereum Prison Key can be obtained by completing the (Non-Heroic) Daily Dungeon Quest given by Nether-Stalker Mah'duun. The key is rewarded regardless of the above mentioned prerequisites.