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In this grid-shading puzzle, each square is either red or white. Some of the red squares may have already been filled in for you. Each row or column is labelled with a string of numbers. The numbers indicate the length of all consecutive runs of red squares, and are displayed in the order that the runs appear in that line. For example, a label "2 1 6" indicates sets of two, one and six red squares, each of which will have at least one white square separating them.

Click on a square to make it red. Click the square again if you have made a mistake and it will return to white.

If you are certain a square should remain white you can double-click it.





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The puzzle was created as a child-accessible version of the puzzle included in the 2015 Christmas cards sent by the director of GCHQ, Britain’s security and intelligence organisation. The puzzle was the first section of a challenging quiz.

As can be seen from the following article which appeared in The Times newspaper in January 2016, the later sections of the GCHQ quiz are particularly difficult.

Report in The Times

The following article appeared on February 5th 2016.

Report in The Times

Successfully complete level 10 of Cryptographic and you will be directed to the GCHQ quiz.


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