The Vigenère Cipher

A more secure way to encode your secret messages.

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The Vigenère Cipher is a more complicated version of the Caeser Cipher than is significantly more difficult to decode. I personally recommend this cipher in an instance that a friend (or perhaps enemy) will try to solve it, but doesn’t have a significant amount of resources. Experienced Government codebreakers and computer tools can break these, so if your goal is to keep classified information from the government, a different cipher may be recommended.

However, if you have a few normal people you don’t want to be reading your message, this cipher is the way to go. It works by choosing a “code word” and using it to encrypt your message.

EXAMPLE:

Secret Message:     ATTACKATDAWN

Code Word:        LEMONLEMONLE

New Message:             LXFOPVEFRNHR 

 

You encrypt the message by using the “Vigenère Square”, shown as an image at the top of the page. To successfully encrypt a message, you would take the “A” from “Attack at Dawn”, and look at the chart. If you’re encoding it with the “L” from “Lemon”, then check the spot where row A and column L intersect. You’ll find another “L”, so that’s what you put in the new message.

Secret Message:     A

Code Word:        L

New Message:             L

 

This technique causes the letters to be much more scrambled than in a normal Caesar Cipher. Because the code word or even the length of the codeword is unknown, it takes much more time and effort to decrypt a Vigenère Cipher.

To use this technique by hand, you can change all the letters into numbers. A = 0, B = 1, etc. Then, add the numbers of the code word and the message. For example, if we were trying to encode the message “Bacon” with our typical code word, “Lemon”, then B would equal 1 and L would equal 11. Add the two numbers. 11 + 1 = 12. The letter assigned to 12 is M, meaning the new encrypted letter would be M. Be warned, however, that many who use this technique label A as 1 instead of 0, so that might cause confusion.

Also note that if the number adds up to “26”  or “27”, or a number too high, then simply go back to A and keep counting.

Now that you’ve learned about that, it’s time to do some decrypting. If you have some time on your hands, give it a try!

Caeser Cipher Message:  Sgd bncdvnqc hr “Etm”.

Vigenère Cipher Message: Bbny’m ltoe kuitlvyy fhbbtf fzvwjwg? Fhfbye nh ptizihgx!

 

The Caeser Cipher Message has a clue inside it to decrypt the Vigenère Cipher Message. Good luck, everyone!

 

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