The next time you need a new Android app to keep the little ones entertained, you should consider turning to the UK's GCHQ intelligence agency. No, really. Infamous for its surveillance capabilities exposed by whistleblower Edward Snowden, the (once) super-secret organisation has now released a kid-friendly tablet app focused on cryptography. Originally developed by GCHQ placement students, the Cryptoy app teaches children about traditional encryption methods such as shift, substitution, Vigenère and Enigma. Youngsters can then apply these techniques to create their own encoded messages and send them on to friends for decryption. Cryptography has come a long way since these classic ciphers were invented, but GCHQ says the basic principles are still relevant for modern code breakers. It's also planning an iOS version for next year, so if your kids are using an iPad they shouldn't be left out for too long. Passing notes around in class will never be the same again.