Thanks for the reply, I'm really pleased with an external opinion, I'm really wasting a lot of energy behind it! You're right, you can recover some bytes by "intuition" in fact now I'm applying some changes and will publish a new version. In particular, the xor function you proposed will be added to the bytes encrypted with my original method, so the xor function will not be "alone" but will be accompanied by the original method of 256 bytes. Furthermore, as you rightly said, even if by merging the two functions are still very secure, it would be much safer if the key has the same length as the input and in fact in the next version the key will be generated especially for the file, or it will be possible to encrypt only a message or a file of maximum length 256 bytes so that the keys do not have to be modified or lengthened. Now I'll see what's best. Once some changes are applied I think it can come in very handy and it's also super lightweight. I'll get to work, I'll put another submit here when it's ready and WELL DONE.