Talk:Orokin Void/@comment-82.14.64.189-20131023171019/@comment-2216622-20131024000239

play survival. 15 minutes will guarantee you a key drop; capture keys have the same chances as all others. the Survival page has more info.

alternatively, you could do Endless Defense. that has a chance to drop keys as well, and possibly at a faster rate, though it's not as guaranteed and thusly i personally have less success with running defense missions for keys.