A while ago I made this encryption code for encoding plain text using a key, then using the same key it decrypts the text. It uses an algorithm similar to a vernier square, however for ASCII character codes instead of just the latin alphabet. It works quite dependably, however unfortunately I was unable to modify it to encrypt zip files as I had hoped (partially due to me not wanting to spend the time to look into the filesystem that zip files use). Anyways, there is a download link below if you want to try it out.