During the Second World War, the British government famously recruited winners of a newspaper cryptic crossword competition to work as code-breakers at Bletchley Park. Now it hopes to use an app for Android tablets to encourage similar skills, needed to tackle emerging cybersecurity threats.

As a result, the usually very-low-profile government surveillance agency GCHQ has found itself in the unexpected situation of publishing an app which it hopes will encourage the next generation of code-breakers.

GCHQ said the Cryptoy app will help users to understand basic encryption techniques, learn about their history, and create their own encoded messages, which can then be shared with friends via social media or email. Recipients can then use the app to try to decipher the messages.

It's mainly aimed at students between the ages of 14 and 16 but can be used by anyone with an interest in learning about or teaching cryptography.

The codes that the app can generate might have been state-of-the-art in the time of Julius Ceasar but most can be broken with a pen and paper. However, as it can also encrypt using Enigma codes as well, users might find having a Colossus handy too.

GCHQ also says the app only asks for very limited permissions and isn't snooping - although thanks to the Edward Snowden revelations, the scale of GCHQ's surveillance is well-documented. For example, according to The Guardian, GCHQ intercepted millions of Yahoo webcam images over a four-year period, whether the users were intelligence targets or not, and has previously attempted to collect data from smartphone apps.

There's more than a little irony in GCHQ using apps and social media to spread knowledge about encryption as its newly appointed director Robert Hannigan recently claimed that social media sites "have become the command-and-control networks of choice for terrorists and criminals" and warned how techniques for encrypting messages or making them anonymous "which were once the preserve of the most sophisticated criminals or nation states now come as standard".

The Cryptoy app was designed by students on an industrial year placement at GCHQ and is part of its attempt to increase the uptake of science, technology, engineering, and maths subjects at schools through its outreach programme. The agency is also involved in other attempts to encourage cybersecurity skills in the UK such as the Cyber Security Challenge.

Even though the examples of cryptography demonstrated by Cryptoy are from an earlier era, the design principles that their inventors used are the same as those of modern cryptographic designers. GCHQ argues it is this similarity in mindset that all cryptographic designers need, whether they were working two thousand years ago or today.

Hannigan said: "Building maths and cyber skills in the younger generation is essential for maintaining the cyber security of the UK and growing a vibrant digital economy."

The Cryptoy app is currently available for download free-of-charge to Android tablets, and GCHQ said it aims to have an iPad version available in 2015.

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