I use a version of this that I made on Turbowarp to send secret messages to my friend. To encrypt: Press the green flag and enter the text you want to encrypt, press enter or the purple ⋱∕ (that's supposed to be a tick mark) and then type in your key. this can be any combination of numbers that the software deems short enough. (You'll get an error message if it's too long) you should remember the key, because you'll need it to decrypt the string of numbers and asterisks that it will give you. Triple-click and Ctrl+C to copy (on PC), and then you can paste it somewhere. If you're on mobile, try long pressing the string. To decrypt: press space (If you're on mobile, tap "see inside" and press on the piece of code with the comment attached to it) and paste the string of numbers and asterisks that the software gave you that you should have stored somewhere safely or that your friend sent you, press enter or the tick mark, and then type in the key. hopefully you'll get the original text more or less as it was at first. Note that this part usually takes the longest.
I copied a variable containing all of the printable ASCII characters from a project by @griffpatch , and I got the idea for this to only be able to support printable ASCII characters from @awesome-llama-test .