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104 CHAPTER 6. DECRYPTING MONOALPHABETIC CIPHERS
Stephen D. Lee, it was suggested that “WILHELMINUSVOLKSVEST”
be used in this manner. The numbering is
W I L H E L M I N U S V O L K S V E S T
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
As H appears only once, there is only one replacement for it. On the other
hand, L appears three times so it has three possible replacements. The
letters that don’t appear in the keyword are numbered at the end, so A is
21, B is 22, and so on.
When used with a long keyphrase the number of replacements for each
letter will mimic how frequently they appear in normal language. If the
substitute for a letter is always randomly chosen from the set of replacements,
then this leads to a very flat frequency count. Hence this method
can produce quite secure ciphertexts. Unfortunately, people tend to get
lazy and generally reuse the same couple of replacements, destroying the
strength of the system.
(a) Routh’s word was later taken up by General Robert E. Lee. He
used it to encipher a message he sent on 23 Nov 1863 [Gaddy]. The
following contains Lee’s location and the name and location of the
intended recipient. Decipher the message.
25 30 13 7 4 29 23 21 12 21 3 30 32 2 9 7 8
11 16 2 19 11 8 28 28 2 26 30 21 9 21 24 21 20
13 23 13 6 22 5 9 27 21 7 8 9 16 1 18 1 14
3 21 21 26 7 5 30 2 24 8 21 9
(b) In June 1864 a Confederate major of Gen. E. Kirby Smith’s trans-
Mississippi command deserted and disclosed a cipher similar to the
one above, based on the word “impersonificationaly” [Gaddy].
Decipher the following silly phrase (designed to take advantage of the
homophones). 1 5 18 17 18 31 18 20 13 8 22 1 2 24 15 22 11 8 23 9
17 2 7 17 14 18 8 13.
8. The most famous cipher story in history is Edgar Allen Poe’s “The Gold
Bug”. First published in 1843, it caused a sensation. By far Poe’s most
popular story, it gave Poe an international reputation as a great cryptography.
In the story, William Legrand is living on an island near South Carolina.
By legend, this island was once the home of the pirate Captain Kidd.
Legrand has found a new species of beetle, a gold-colored one. He draws a
picture of this bug to show to a friend. It happens that the paper he uses
contains a secret message written in invisible ink that just so happens to
become visible when the friend just so happens to hold the paper close,
but not too close, to a fire. Here is the message.