Talk:Hextech Crafting/@comment-5116121-20160324211759/@comment-24176467-20160326144114

Keys, perhaps unsurprisingly, open chests. Key fragments will sometimes drop after victory in any matchmade game mode--unlike chests, you can earn keys in ARAM or Twisted Treeline. Three key fragments can be forged into a single key; you can also purchase keys through the store for RP. Key fragments drop a little more frequently when you play with friends!

https://support.riotgames.com/hc/en-us/articles/207884233-Hextech-Crafting-Guide