Just for interest, here's another way you can shuffle the alphabet to create a range of codes. Start with the complete alphabet spaced equally round one large circle and also on another circle which will fit into the first circle.
You then place the smaller circle in the centre of the larger circle and line the letters up in different ways. Here's an example:
You have to make absolutely sure that your two circles of alphabet letters line up properly. If you create them on your computer, use a monospaced font. It might take a few tries to get it right. (I created my circles of letters by using the 'Align text to path' tool in CorelDRAW.) On the other hand, you could print this page or save the top graphic to your computer and print it with your word processor or graphics program. You could then cut out the circles and paste them onto pieces of card with some sort of pin in the centre.
If my Maths is correct, this will enable you to produce 676 different codes. You will then be presented with a wonderful new challenge: How do you tell the receiver of your message, in code, which code you are using?