Alan Woodward is a visiting professor at the University of Surreys department of computing. In this article he shows how to crack the code-cracking puzzle set by GCHQ, in its hunt for new recruits. We decided at the time not to reveal the answers to the puzzle, but enough time has now passed so we can explain (to those who werent able to crack it) how to do it. The first puzzle is on the page you see in your browser. It contains a series of characters: 143 characters, which just happens to be the product of two prime numbers: 11 and 13.”]
Source: https://grahamcluley.com/gchq-hacker-recruitment-puzzle/