Talk:Void Keys/@comment-184.162.33.117-20160107104158

This isn't true, you can obtain them from excavation if the level is high enough (hieracon pluto). Since it shares survival drop table I'd guess they can also drop in survival but I did not test it. I'd edit out the the "only" part, but I don't seem to be able to do so.
 * Interception Missions - Only missions where Tower IV keys can be acquired. Click to see rewards table.