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

134 CHAPTER 7.
VIGENÈRE CIPHERS
ii) Putting a pair with a letter says to use the keyletter corresponding to
the second number of the pair to encipher this letter. The first and last
number of the result tells how many nulls are at the front and rear of the
message. So (1.2)Q says encipher Q with R - gives 04, says no nulls at
start, 4 at rear.
iii) Deliberately misspelling words, by leaving out letters or adding extra
letters, would increase safety.
(a) Dodgson gives as an example
(2.3)(V)10.14.20.00.00.01.33.40.42.40.01.20.23.02.
Decipher it.
(b) Dodgson added that an “improvement on this again is instead of
03 to write D ... and so on.” Explain why this makes his system a
Variant Beaufort system.
27. As Vigenére said, ”the longer the key is, the more difficult it is to solve the
cipher.” Does using words that have some repetition in them, like Banana,
Concoct, Tomorrow or Rococo Change this conclusion
28. As the end of World War II drew near, plans were drawn up for the
future of the SSA. Included in this were studies of the history of U.S.
cryptography prepared under the Direction of the Chief Signal Officer.
The following quote is from the study Codes and Ciphers during the Civil
War dated 20 April 1945.
Careful use of Vigenère requires [the] cipher clerk to first underline
any repetitions in the body of the plaintext. Then copy the text into
columns under the keyword/phrase and make sure that none of these
repetitions appear in the same column, and if any do, insert nulls to
throw the repetition out of phase.
Explain what this quote means. That is, explain what the underlining is
trying to accomplish.
29. In his column in Philadelphia’s Alexander’s Weekly Messenger Edgar
Allen Poe challenged readers that he could break any monoalphabetically
enciphered text. A Mr. G. W. Kulp sent the ciphertext
GEIEI ASGDX VZIJQ LMWLA AMXZY ZMLWD YXRTV JCIML LHJXA MXZYF IFIWA
FEPML BGPXW DLNRW EQWBC KMHJT NWSLB RZLEW MKDTC HUCMK WZZXN TGUIE
LBRJL HTAIV UGMBX LKIUU PAMUM WXKJX EWEQM CZXZL GNSBW LBRNT YOLPI
MLQIH WKXKW IOLXE UFBXV V
that was published February 26th, 1840. Poe showed in a later issue that
the ciphertext was not a monoalphabetic cipher, and called it “A jargon
of random characters having no meaning whatsoever.” Indeed, it is a
Vigenère cipher. Even knowing this does not necessarily make this an
easy text to break. Can you do it