The first puzzle is a super-fun 25×25 nonogram puzzle

Before Christmas, the benign megasurveillance bods at GCHQ released a set of festive puzzles, in the form of a Christmas card and associated website. An initial nonogram puzzle led to a sequence of increasingly fiendish teasers, and solvers of the final set of puzzles were invited to email in their answers, with the correctest winning a fancy paperweight, signed book and, GCHQ were at pains to stress, not an Imitation-Game-style secret job offer.

GCHQ have now given provided the full solution and vague biographical details of the three people closest to a complete set of correct answers. The Guardian have broken the spies’ code of silence, naming and indeed interviewing one of the winners, mathematician and former Fifteen To One winner David McBryan.

The puzzles are still available for anyone who want to have a go. Aperiodical readers may be particularly interested in Part 4 which consists of three integer sequences (reviews forthcoming), but all parts of the competition include a fair smattering of maths.

More information

A Christmas card with a cryptographic twist for charity – the starting point for the puzzles

Director GCHQ’s Christmas card puzzle – how did you do? – post announcing the results, including a link to the solutions PDF