- The Key of Destruction drops from Odeg the Keywarden in Act I - Fields of Misery
- The Key of Hate drops from Sokahr the Keywarden in Act II - Dahlgur Oasis
- The Key of Terror drops from Xah'Rith the Keywarden in Act III - Stonefort
- The Infernal Machine Blacksmithing Plans drop from Nekarat the Keywarden in Act IV - Silver Spire Level 1 (Note: You only need to farm the plans once) - Patch 1.0.8 Update: Nekarat will now also drop random keys!
Players can only encounter the Keywardens in the Inferno difficulty will they have a chance to drop pieces of the Infernal Machine. While Monster Power is not required, each level will increase the drop rate of both the keys and the plans by 10%, all the way up to a guaranteed 100% drop chance at Monster Power 10.
How to to turn on Monster Power: Go into Options > Gameplay and look for "Enable Monster Power Selection". There is currently a bug where the MP option turns off randomly, and you will have to go into the options and turn it on again. After enabling it, you can select a monster power level in the quest selection menu. (1.0.8 update, this bug seems to have been fixed.)