I made a functioning program where you can put in a message (paragraphs worth even) and get a string of numbers in return. This string can be different even if you put in the same sentence twice, so it's extra hard to crack. You can put coded messages in the decoder and get the sentence back.

Fun feature, you can put a already coded message in the coder again to get a double coded message! You will have to decode it twice though.

Message Coder/Decoder