# Have You Tried Turning It Off And On Again? (Vigenere cipher)

So here's a little puzzle for all of the IT crowd out there.

It demonstrates the Vigenere cipher, the unexpectedly strong 'chiffre indéchiffrable'. The Wikipedia description explains how you can use the tabula recta to decode it.

Each row starts with a key letter. The remainder of the row holds the letters A to Z (in shifted order). Although there are 26 key rows shown, you will only use as many keys (different alphabets) as there are unique letters in the key string, here just 5 keys, {L, E, M, O, N}. For successive letters of the message, we are going to take successive letters of the key string, and encipher each message letter using its corresponding key row. Choose the next letter of the key, go along that row to find the column heading that matches the message character; the letter at the intersection of [key-row, msg-col] is the enciphered letter.

If you can't be bothered to do it by hand then there's a handy converter here at cryptii.com, which can handle a bunch of common ciphers.

WEMGO ZJLD EGH XJCD ELW

Let the countdown begin!

• The solution is a short series of English dictionary words.

• The key length is 9 characters.

OK, well evidently one of the things to watch for when setting this type of puzzle is that if you don't specify enough details of the plaintext or the key then the plaintext can be anything which fits the word boundaries. ;) Thank you Sp3000 for pointing this out in such an entertaining way.

• How long is the key? What if the key length was as long as the message? Commented Nov 19, 2014 at 12:24
• In that case I'm going to have fun picking a key :D Commented Nov 19, 2014 at 12:46
• Is the key a "common" word too? Commented Nov 19, 2014 at 14:05
• I think I'll have to stop for today - a key length of 9 is actually quite long, since each letter of the key only affects 2/3 letters in the cipher text (making frequency counting a lot less useful)... Commented Nov 19, 2014 at 14:06
• @AE I wrote one, but the search space is big :( Commented Nov 19, 2014 at 14:11

Well, I AM a giddy goat.

As a fan of

The IT Crowd,

I knew there was some connection but couldn't flipping put it together, until I realized

Let the countdown begin!

is a reference to

The Final Countdown (Season 4 Episode 2), in which (as Wikipedia describes it) "Moss stuns everyone by declaring that the 9 letter string TNETENNBA is in fact a word."

Obviously, that makes the key:

and the deciphered text:

DRINK MILK AND KICK ASS (from a Moss quote from the same episode: "I came here to drink milk and kick ass. And I've just finished my milk.")

I regret not asking if the 9-letter key could be used in a sentence.

• HOORAY! Well done! :)
– A E
Commented Nov 20, 2014 at 17:10
• (I checked that it was also possible to get that by GoogleFu, one didn't have to be a fan).
– A E
Commented Nov 20, 2014 at 17:17

This was posted before A.E. specified the key length, just to highlight what happens if you don't :P

The near-pangram "key" is: