We’ve discussed ciphers and codecracking numerous times in the past, and rightly so. It’s a style of puzzling that has literally affected the outcomes of battles, helped shape key historical moments, and changed the face of spycraft.

And it’s a puzzle form that continues to evolve to this day. We’ve moved far beyond the simple one-to-one replacement encryptions of your standard newspaper cryptogram, and intrepid solvers are always looking for newer and more devious ways to conceal their messages.

Tumblr user Cipherface has cooked up a pretty ingenious system that actually uses another style of puzzling in its execution: crosswords.

Here’s how it works. You write your message out in the open spaces of the crossword, ignoring the black squares.

Then, map out this diagonal path as the first step to encrypting your message.

Do the same with the puzzle’s answer key, and you’ve got your running key, the text used to substitute letters for the letters in your actual message.

Then you run your message through the tabula recta, a table where you use the letter you want revealed and the letter in your running key to pick the letter in your encryption.

Here, we can see Cipherface mapping out the encrypted message using this method.

From the Tumblr writeup:

The idea is to use a crossword puzzle for the transposition and the answers to the previous weeks puzzle as a running key. And the blank spaces are used to insert nulls into the final ciphertext. You then mail it to a friend who uses the date it was mailed to decide which puzzle to use for decryption.

It’s a pretty clever way to leave your encryption key in plain sight, and yet keep your messages secret. The running key keeps changing, so it’s more effective than traditional running keys, which stayed the same for longer periods of time.

Not to mention, using the puzzle’s publishing date? What a quick and easy way to keep your friend informed in an innocuous way. You’d just need to decide ahead of time which newspaper to use.

And it figures. The best way to make a puzzle better? Add another puzzle.

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