A Vigenère cipher works like this:
- Suppose you want to encode the following message from Bob Dole: "I don't think my campaign is in that much trouble."
- First, you pick your keywordwhich in our case will be STIM.
- Then you write the keyword over the top of the message, letter by letter, repeating the keyword over and over again, until you've covered over the whole message. In our case, it would look like this:
STIM S TIMST IM STIMSTIM ST IM STIMSTIM STIMSTI
I don't think my campaign is in that much trouble.
- Now you go to your "Vigenère tableau," which is as represented below:
- You use this tableau to encode each letter of the mesrage. The vertical alphabet on the far left represents which code you'll use (these are the "rows"); the horizontal alphabet on the top represents the un-encoded letters in the message (these are the "columns").
- Begin by looking at your message. Start with the first letter in the textwhich in this case is the letter I. Look at the keyword letter written on top of this letterin this case, it's an S.
- That means you'll use the S cipher to encrypt the first letter I. So you look to the column on the far left, and go down until you get to the row that begins with the letter S. Then go across until you get to the column that, at the top, is the letter I. The point where the row and the column intersect is your encrypted letterwhich, in this case, is the letter A.
- Continue on to the next letter in your message. This time, you're encrypting the letter D using the T codewhich would result in the encrypted letter W.
- Carry on until the endand marvel at how totally brain-numbing the whole process is. The final product, by the way, results in the following message:
A WWZ'L MPUFD UK UTUBSBOZ AL QZ LAIFENKT LKWGTEM.