Secret Messages 101

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Note: The terms "code" and "cipher" have specific meanings to the cryptologist... but we're not going to worry about that right now. This is a very basic tutorial and if you are interested in the subject enough to progress, you will eventually learn the various meanings of similar terms.

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Who knows when people first tried to send secret messages? Was it some caveboy looking at his neighbor cavegirl and saying ugh, ugh, with a big sloppy smile, whereupon the alpha male quickly broke the code and whacked the caveboy? Who knows. We do know that the attempt to send hidden messages has been going on for thousands of years, and it still hasn't reached what you can call "perfection".
Still, you can put messages to code that is effective for the purpose involved. Each message has a period of time where it is valuable, beyond which the message is useless to the "enemy" even if they decode it. For instance, a message in a warzone may have a life span of only a few hours, or it may be valuable for a long time. The longer the lifespan, the more complicated and secure the code must be to protect the message.

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Types of

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"Poly" [Gr. polys] a combining form meaning "much".
"Alphabetic"[Gr. alpha +beta] the letters used in writing a language, arranged in a traditional order.

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The Vigenere Square is a basic PolyAlphabetic table, and is one way to encipher and decipher a message. Suppose you want to send this message to your friend:
HELLO BUBBA   Make up a password (another name for it is "keyword") that has no duplicate letters. It does not need to be a "real" word. For this example let's use the password/keyword of CIPHER.   write the keyword below the message as many times as needed so that every letter in the message has a corresponding keyword letter.
Message: H E L L O B U B B A
Keyword: C I P H E R C I P H
  Now look at the table. Find the first letter of the message (H) on the top row alphabet. Next find the first letter of the keyword (C) on the column running down the left side of the square. Trace the two paths until you find the square where the H row meets the C column (J). Keep going until you encode the entire message. Your coded message will read:
??????????????
  To DEcipher the message, write the keyword above the coded message:
Keyword: C I P H E R C I P H
Message: J ? ? ? ? ? ? ? ? ?
  Find the first letter of the keyword (C) in the alphabet running down the left side of the square. Move your finger along this row until you meet the first letter of the coded message (J). Now run up from the J until you reach the top reference alphabet row. This gives you the letter (?). Now, use the Vigenere Square to practice enciphering and deciphering two coded messages of your own choice:
Your keyword is: _ _ _ _ _ _ _ _ (make up your own)
Your message is: _ _ _ _ _ _ _ _ (make up your own)
Your Encoded message is: _ _ _ _ _ _ _ _ ...
Your Decoded message is: _ _ _ _ _ _ _ _ ...
  Let whoever gave you this exercise know if you made it work, and have them practice with you for an occasional message. Remember, each party to the message will need to have a copy of the table, as well as the keyword and the encrypted message in order to decrypt the message. Of course, if your enemy gets a copy of the table, or even just gets your "keyword", without your table, they will be able to break your code eventually.
Good luck in using the PolyAlphabetic code table! Maybe you have a future in security and counter-espionage!
If you have InterNet access, you may want to visit some of these websites for further security information:

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References used or quoted in this tutorial:
(1)Webster's New World Dictionary ©1979 Simon & Shuster.
(2)
(3)
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