A locksmith villager

The locksmith can trade with you giving you keys for different things. Keys to lock and open an iron door and iron chess. Keys to a special temple in the swamp that has iron related loot and secret doors to top tier loot, secret underground iron ruins that have a chance of giving you an enchanted key that gives you access to a secret ruin in the End that have unbreaking 3 and 1or 2 mending books by chance and 5 golden enchanted apples with 1 ancient debris by chance.

The key of security can be crafted with iron ingots or gold ingots with cobblestone

4 cobblestone with 1 iron ingot or 1 gold ingot

key with iron ingots can open one iron chest or iron door at a time, key with gold can open and close up to 5 different chest and iron doors at a time

The key of swamp temple can be crafted with amethyst shard and iron ingots 

4 amethyst shard and 1 iron ingot

The key of the secret undergrounds can be crafted with obsidian blocks and diamond ingots 

4 obsidian and 1 diamond

The key of the enchanted cannot be crafted you must find it in unground ruins which is quite rare to find.

The key of enchanted has a 60% of being found in an unground ruin

1. Key of security- allows you to lock and open iron doors and iron chest.
2. Key of swamp temple- allows you to open and close secret doors in the swamp temple.
3. Key of the secret undergrounds- open and close secret underground iron ruins.
4. Key of the enchanted- allows you to open and close secret end ruins.