Monday, May 5, 2008

The Vigenere Cipher

As promised, here is some information about the famous, or infamous Vigenere cipher. A Vigenere Square or Tablet is shown here and is used to encode and decipher messages using the Vigenere cipher. The Vigenere cipher is actually a series of another cipher known as a Caesar cipher.

The Vigenere cipher has been around since the 1500s. A book was written about it explaining how the cipher worked in 1553. Even though the cipher was explained in the book, to the novice the Vigenere cipher was thought to be unbreakable. This proved to be a very big mistake for the South during the Civil War. Apparently the people in charge of their codes would be considered novices.

In an effort not to confuse anyone I have taken the liberty of copying the explanation of the Vigenere cipher from the Wikipidia page. This way I don’t screw it up!

“In a Caesar cipher, each letter of the alphabet is shifted along some number of places; for example, in a Caesar cipher of shift 3, A would become D, B would become E and so on. The Vigenère cipher consists of several Caesar ciphers in sequence with different shift values.”
“To encipher, a table of alphabets can be used, termed a tabula recta, Vigenère square, or Vigenère table. It consists of the alphabet written out 26 times in different rows, each alphabet shifted cyclically to the left compared to the previous alphabet, corresponding to the 26 possible Caesar ciphers. At different points in the encryption process, the cipher uses a different alphabet from one of the rows. The alphabet used at each point depends on a repeating keyword.”
“For example, suppose that the plaintext to be encrypted is:” ATTACKATDAWN

“The person sending the message chooses a keyword and repeats it until it matches the length of the plaintext, for example, the keyword "LEMON":” LEMONLEMONLE

“The first letter of the plaintext, A, is enciphered using the alphabet in row L, which is the first letter of the key. This is done by looking at the letter in row L and column A of the Vigenère square, namely L. Similarly, for the second letter of the plaintext, the second letter of the key is used; the letter at row E and column T is X. The rest of the plaintext is enciphered in a similar fashion:”


“Decryption is performed by finding the position of the ciphertext letter in a row of the table, and then taking the label of the column in which it appears as the plaintext. For example, in row L, the ciphertext L appears in column A, which taken as the first plaintext letter. The second letter is decrypted by looking up X in row E of the table; it appears in column T, which is taken as the plaintext letter.”

To symplify things in the field the South was known to use a Cipher Disk. This was a disk with the alphabet in a cirlce around the outside of the disk and a second smaller disk that turned on the inside with it’s own alphabet around the outside of the smaller disk.

To make all of this work you had to have a key word or phrase. The South was known to regularly use three key phrases. The first two, COMPLETE VICTORY and MANCHESTER BLUFF, were used continuosly during the Civil War. As the war got closer to the end and the South saw that they were in trouble they also began using the key phrase of COME RETRIBUTION. There was a fourth key phrase attributed to the South but I have not been able to verify that this phrase was actually used. That fourth key phrase is said to be JEFFERSONS FERRY.

As an added bonus for blog readers I am listing another key that was discovered by a college professor, and I believe it was discovered sometime in the 1990’s while he was looking at some old Civil War documents. This was a key word and not a phrase and was identified as BALTIMORE. This will be a news flash to more than one KGC researcher.

Here’s my thought for the day. The Knights of the Golden Circle was supposed to be a super secret organization with members so smart that they hid billions of dollars in treasure using a coding system that treasure hunters for more than a century haven’t been able to figure out, right? So who in that brain trust decided to use centuries old ciphers that were known to other code breakers to pass secret messages back and forth during the Civil War? If they couldn’t come up with their own ciphers to encode their most important messages, how did they come up with their own elaborate code to hide treasure?

1 comment:

Anonymous said...

What about the use of the KGC Cipher that was found in the Bickley files at the National Archives? This was an original code that by all appearances that would not have been "so easy" for federal agents to figure out. I would not be able to tell you if this code was used often as I have not researched it, but it seems this could possibly be a more original code used by the KGC as opposed to the "ancient ciphers" you have described.