Call of Duty: Black Ops 3 features a Black Market, which is a place for players to get Supply Drops. These Supply Drops contain items that are cosmetic – attachment variants, taunts, gestures, and more. In order to get a Supply Drop from the Black Market you have to use an in-game currency called Cryptokey.
There are two types of Supply Drops available: Common Supply Drop and Rare Supply Drop. Common Supply Drop is 10 Cryptokey. Rare are 40 Cryptokey.
It looks like players are able to earn these via playing matches in the game. Players should see their Cryptokeys progress in the After Action Report screen and in the Black Market in game.