I made a cipher!
This cipher is pretty basic, but pretty much uncrackable. It uses a key to shift each individual character by some amount, so you can only decode it if you have the key. It would take years to brute-force it. If you have both the input and output, you could probably derive the key, but someone with both of those theoretically should have both and wouldn't need to in the first place.
Check it out right here under my projects! https://nerdcraftdev.benjaminrose.com/projects/cipher