How it works:
1. Craft a key

2. Rename it in the anvil to your password

3. Shift + right click on the block to lock it!

Shift + right-clicking with any key will unlock the block (only if you are the owner of it)

Locked blocks are unbreakable by any means (explosions, fire, others)
only the owner of the block can destroy it or someone who holds a key in their main hand (or you can unlock it with the key and then break it)

There is also a ender key that works the same way just it allows you to randomize the passowrd (bt right-clicking in the air) upon linking to a block (a link is created when you lock the block with the key)
Otherwise it works the same as a normal key

Maybe I will add a config option for this

A full list of lockable blocks:
Beacon
Brewing Stand
Chest
Dispenser
Hopper
Furnace
Dropper

Disclaimer:
This is not my project and I am not claiming it as mine, credits to the original mod and the creator are https://www.curseforge.com/minecraft/mc-mods/simple-chest-locker.

I only re-posted this because there is an issue on the original one that doesn't let you launch the game and prevents you from using the mod which is now fixed in the one I am posting. I will not be making any updates or anything for this mod as it is not mine, I am simply providing a fixed version for the mod as it did not work.

Simple Chest Locker *Fixed*

Simple Chest Locker Fixed