I
hate maths, but making your own little cypher is cool. You can use a free ASCII to binary converter to change your text into numbers. Now you can use simple calculations to change the number and give your friend the cypher.
Try to work this out...
59376640
I'll give you a clue - It uses 2 calculations, 1 is multiply and the other's divide.
You can make your own as complex as you want, just reverse the order, and use the inverse tool to which you encoded it with (+ becomes minus, / becomes *, etc.)
If you can take that number and turn it into 1s and 0s in 2 steps, then you can change it to its ASCII equivalent and discover the message.
This has "Fiasco" written all over it.