Some hints which may help you:
- Try to find out how long a character will be encrypted
- What will happen if you encrypt multipe times the same character (aaaaa)?
- What will happen if you encrypt some characters which follows on each other (abcde)
- The '0' often will help you to get an idea.
- Will you get always the same result if you encrypte the same text again? (hard level)
Dont despair :)
And have fun!