How to get keys?

you have a chance to get one after wining a game, a chance is not gurantee. Also every key you get on a month diminished the chance to get the following key so the first 4 or 5 keys are quiet easy to get but it gets quite hard after that if you are on a team or group then you are more likely to get a key than playing alone

The chance diminishes with each fragment you get, but that chance resets roughly 30 days after your first fragment.

Apparently theres a 12 fragment/month cap as well, so the drop rate can drop to 0 if you play a lot/get lucky with your wins.