To the people who say it's supposed to be rare. I ran the nightfall 9 times this week and 3 times last week with no drops. A lot of heroic strikes 30+ and got 1 key, and I ran 16 normal strikes and got 2 keys. It's all random. They should make a bounty to get a guaranteed key like doing the nightfall, 5 heroic strikes and 3 normal ones.