"This item allows you to unlock a locked loot box."
This item is a drop from mobs in game.
It can also drop from any Steel-bound Lootboxs.
And is a reward from the 3-Year Giftbox
Sturdy Steel Keys bought from the Turbine Store are always Bound to the Account, where as the ones that drop from mobs in game or lootboxes can be traded.
You can win this item from the Lottery: Lottery of Angrenost and/or Welcome Wagon Lottery and/or Lottery of Rhovanion and/or Lottery of the Free Peoples and/or Lottery of the Northlands and/or Lottery of the Depths and/or It's key! and/or Boxes and Keys Lottery and/or Steel Box and Key of which you can enter at http://my.lotro.com/home/lottery.