Cryptology - Unofficial St. Mary's College of California Web Site

132 CHAPTER 7.
VIGENÈRE CIPHERS
24. (Continuation of 23.) In I, Claudius by Robert Graves, the character
Claudius writes
The key of the ... cipher ... was provided by the first hundred lines
of the first book of the Iliad, which had to be read concurrently with
the writing of the cipher, each letter in the writing being represented
by the number of letters of the alphabet intervening between it and
the corresponding letter in Homer. Thus the first letter of the first
word of the first line of the first book of the Iliad is Mu. Suppose the
first letter of the first word of an entry in the dossier to be Upsilon.
There are seven letters in the Greek alphabet intervening between
Mu and Upsilon so Upsilon would be written as 7. In this plan the
alphabet wouild be thought of as circular, Omega, the last letter,
following Alpha, the first, so that the distance between Upsilon and
Alpha would be 4, but the distance between Alpha and Upsilon sould
be 18. It was Augustus’s invention and must have taken rather a long
time to write and decode.
Although Graves describes a cipher using Greek, it should not be Greek
to you. (Sorry – couldn’t resist.) This is clearly a polyalphabetic cipher.
What kind – Vigenére, Beaufort or Variant
If it helps, the Greek alphabet is
αβγδɛζηθικλµνξoπρστυφχψω
25. Admiral Beaufort was neither the first nor the last person to invent the
cipher named for him. In his diary on April 22, 1868 Charles Dodgson
wrote that while “Sitting up at night I invented a new cipher, which I think
of calling the Telegraph Cipher.” He told George Ward Hunt, First Lord
of the Admiralty about his invention. No response is known [Abeles2].
His method involves two alphabets:
Key Alphabet: ABCDEFGHIJKLMNOPQRSTUVWXYZ
Message Alphabet: abcdefghijklmnopqrstuvwxyza
“To translate a message into cipher, write the key-word, letter for
letter, over the message, repeating it as often as may be necessary:
slide the message-alphabet along under the other, so as to bring the
first letter of the message under the first letter of the key-word, and
copy the letter that stands over ’a’: then do the same with the second
letter of the message and the second letter of the key-word, and so
on.
Translate back into English by the same process.
For example, if the key-word be WAR, and the message meet me at
six, we write it thus:–
warw ar wa rwa
meet me at six
kwnd on wh zod