Edinburgh man cracks GCHQ's cryptography challenge

David McBryan, from Holyrood, battled through five rounds and beat 600,000 people to come the closest to fully solving the series of challenges set by director of GCHQ Robert Hannigan in his Christmas card.

David, one of three people to have reached that stage, said the possibility of winning was “driving him along” as he attempted to outsmart the GCHQ cryptographers.

The 41-year-old, originally from Dublin, said: “I thought I had solved it, but a report came out a few days ago saying nobody had . . . so I went back and had another look and figured out what I missed, but I was too late at that point.

“But it seems that everyone else missed it as well and I was joint closest.

“It was challenging – a very well-constructed set of puzzles, I’d recommend it to anyone actually. It’s enjoyable, but it’s tough.”

Mr McBryan, a former Fifteen to One game show winner who now writes questions for the show and pub quizzes, studied maths and artificial intelligence at university.

He said “logical rigorous thinking” was needed to be a good puzzle-solver but that “most of all it’s got to be just the experience of doing puzzles – the more you do the better you’ll get at it”.

The compendium of word and number puzzles took a team of eight GCHQ cryptographers two months to compile, and included a mix of past and fresh challenges – with plenty of hidden material.

The first stage was a grid-shading exercise which, when completed, revealed a scannable QR bar code to direct people to the next part.

Puzzlers then had to work out URLs and IP addresses by solving a series of clues until they reached the final stage.

Mr McBryan said: “Once you got through there’s no confirmation whether you’re on the right track or whether you got the right set of answers and that’s one of the most frustrating aspects of it. So you need to be fairly obsessive to keep plugging away at it and trying different things.

“For a long time after I got all the solutions I was still looking for more, because you’ve got no idea if you’ve got it all.”

Thirty thousand people made it through to the final stage and 550 of those submitted answers.

Of the answers, six were considered “complete” by the team of cryptographers, who chose the final three winners based on the quality of their reasoning.

GCHQ denied that the puzzle was an elaborate ploy to recruit fresh talent to its ranks, but said the winners, like anyone else, were “welcome to apply” for jobs.

Each winner will receive a GCHQ paperweight, pen and signed copy of the book Alan Turing Decoded, written by Turing’s nephew Dermot Turing.

The two other winners are Wim Hulpia, 40, from Belgium, and American-born Kelley Kirklin, 54, who lives in London.