The British Information Service GCHQ today released an application called Cryptoy and aims to teach cryptography to children of the secondary educations (and their teachers).
The tool is available for free for any Android tablets. Android phones and iOS devices are not currently supported – but will be next year.
The application is the evolution of one that is designed for it Cheltenham Science Festival, and allows to users of learning basic encryption techniques and their history. It also allows them to write their own coded messages.
Of course, the idea is that these messages will then circulate (via the normal channels) and the recipients will be able to use the application to decrypt them.
Regardless of whether you are a student or not, if you are interested in cryptography, you can try the application.