A still from the TV series Intelligence, showing the life of GCHQ staff inside the office.

On 13 December, the UK's intelligence, cybersecurity and security (GCHQ) special agency released an annual Christmas card. There are seven puzzles of different difficulty levels for children from 11 to 18 years old.

CNN explained that this is how agency employees are looking for smart and talented children who can then go to work at the agency and write themselves in history along with Alan Turing and other cryptographic professionals who collaborated with GCHQ and its predecessors.

Notably, in past years, GCHQ has issued Christmas cards with riddles so complex that even GCHQ staff members could not solve them. In 2016, only three people out of 600,000 applicants who submitted answers were able to correctly solve the most difficult riddle.

Riddles from GCHQ.

bbabo.Net