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

10.9. TRANSPOSITION DURING THE CIVIL WAR 205
By 1863 the ciphers had become more complicated.
Example: (From [Weber, pages 114-5].) Here is the plaintext message.
Headquarters Department of the Cumberland
Chattanooga, October 16, 1863 - 7 p.m.
Major-General Burnside,
Knoxville, Tenn.;
The enemy are preparing pontoons and increasing on our front. If they
cross between us you will go up, and probably we too. You ought to move
in the direction, at least as far as Kingston, which should be strongly
fortified, and your spare stores go into it without delay. You ought to
be free to oppose a crossing of the river, and with your cavalry to keep
open complete and rapid communications between us, so that we can
move combined on him. Let me hear from you, if possible, at once. No
news from you in ten days. Our cavalry drove the rebel raid across the
Tennessee at Lab’s Ferry, with loss to them of 2,000 killed, wounded,
prisoners, and deserters; also five pieces of artillery.
Yours,
Rosecrans
Answer quick.
To encipher we first choose a key: Enemy. This keyword demands that we
use an array with 10 rows of 6 columns each. So we enter the first 60 words of
the message:
For Burnside The enemy are preparing
Pontoons & increasing numbers on our
front If they cross between us
you will go up and probably
we too . You ought to
move in this direction at least
as far as Kingston which should
be strongly fortified and your spare
stores go into it without delay
You ought to be fee to
Next, some giveaway words are replaced by their code equivalents as the
code indicates: Burnside becomes BURTON and enemy becomes WILEY. The key
also indicates that nulls are to be added at the tops and bottoms of certain
columns. After doing this we have
boy greatly
For BURTON the WILEY are preparing
Pontoons & increasing numbers on our
front If they cross between us
you will go up and probably
we too . You ought to
move in this direction at least
as far as Kingston which should
be strongly fortified and your spare
stores go into it without delay
You ought to be free to
Not surely some
Finally, the key tells how the plaintext is to be taken off: D3, U4, D2, U5, D1