The Government Communications Headquarters (GCHQ) houses some of the U.K.'s top cryptographers, spies, and intelligence agents. It’s perhaps not a surprise, then, that their Christmas card features a fiendish cryptic puzzle.
The card was sent by GCHQ director Robert Hannigan to everybody on the organization's Christmas card list. However, if you happen not to be a high-ranking intelligence agent, they also released the puzzle to the public. The GCHQ invites people who enjoyed the puzzle to get into the Christmas spirit and donate to the National Society for the Prevention of Cruelty to Children (NSPCC).
Here's how it works:
The puzzle is all about shading certain squares black and leaving others white.
The numbers on the side of the grid indicate how many consecutive black squares there will be in each row or column. There has to be at least one white square between each run of black squares.
In their press release, GCHQ explained: “For example, a label "2 1 6" indicates sets of two, one and six black squares, each of which will have at least one white square separating them.”
To start, color in the squares where there’s only one possible pattern where the black squares fit (there’s a few of them).
If you're sharp enough to pick up on the clues, the completion of this puzzle should lead you to the next level of brain-teasers.
Click here for a higher resolution version of the puzzle, and check out the GCHQ website for more details.
Image credit: GCHQ