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10.10. THE BATTLE OF THE CIVIL WAR CIPHERS 207
If [the jumble] were used twice or three times, I could, by comparison &
trial, probably decipher the whole business. But if the jumble were not
repeated, I could never decipher it without getting another message in the
same jumble in order to compare the two. ... I found one pair of words
which certainly belonged together, ‘Lambs’ & ‘ferry’ – for there was a
‘Lamb’s Ferry’ on the Tennessee River. But it only made the demonstration
absolute that the jumble ws not repeated [and so I could not make
sense of it.] I afterward found that the Federals made their jumbles by
means of diagrams of row & columns, writing up & down in different orders
& then taking the words across ... They also used some blind words
to further confuse the cipher. This made, indeed, a most excellent cipher,
quick & easy, both to write & to decipher, which is a very great advantage.
But there is one objection to it, in that it required a book, & that
book might get into the wrong hands.
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10.10 The Battle of the Civil War Ciphers
The ciphers used during the Civil War give an interesting comparison. The
North used relatively simple word transposition ciphers, which sends the plaintext,
only jumbled. The South used what was thought to be the unbreakable
Vigenére cipher. Why, then, did the North enjoy more success, cryptographically
There are several reasons. The North’s use of meaningful word in their
reduced the number of garbles, errors, while Vigenére ciphertexts, which have
no context, had many more errors [Weber]. The extensive use of code words
in Stager’s system generally prevented the South from getting any easy entries
into a message. Conversely, the clumsy use of Vigenére (the failure to encipher
the entire message, keeping word lengths) by the South gave the codebreakers
of the North many clues about the message. Having a very few number of keys
also contributed to the weakness of the South’s cryptography. “Judged by the
standards of its own day, [Stager’s] cipher was adequate: it was not too complex
to be practicable, and yet it delayed solution for a sufficient time.” [SSA2, page
20].
10.11 Summary
Transposition Ciphers receive their security by the manner in which they mix
the letters of the plaintext. There are many methods for providing this mixing;
route ciphers, grilles and columnar transposition being the most famous, with
the latter being by far the most popular.
To perform a columnar transposition first select a keyword. Write the plaintext
underneath the keyword, in as many columns as the keyword has letters.