A key is provided with the lock. Without the key, a creature proficient with thieves’ tools can pick this lock with a successful DC 15 Dexterity check. Your GM may decide that better locks are available for higher prices.
RollQuest ships the D&D 2014 SRD as a content pack, on a 5e character sheet that does the maths - roll from the sheet and let the numbers work themselves out. Free to start.