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

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Examples: Encipher or decipher the following names.
(1) Encipher Gaius.
To encipher we move from plaintext alphabet to ciphertext alphabet, that
is, replace each of the plaintext letters gaius by the corresponding ciphertext
letters (underneath them):
So JDLXV is the answer.
(2) Encipher Cleopatra.
(3) Decipher SRPSHB.
g a i u s
J D L X V
To decipher we move from the ciphertext alphabet back to the plaintext
alphabet.
So pompey is the answer.
(4) Decipher FUDVVXV. 5
S R P S H B
p o m p e y
⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄
In Caesar’s time his cipher was likely a good one. After all, it was the first
one ever invented! 6 But once it is known that shifting three forwards and three
back is the key, the secrecy is lost. To try to regain it we might instead agree
ahead of time on a secret number that tells the amount we will shift each letter.
Examples: Encipher or decipher using the given shift amount.
(1) Encipher Augustus using a shift amount of 1. The counting here is simple
– replace each letter by the next one, so a by b, u by V, etc. 7
(2) Encipher Quintillis using a shift amount of 10.
Quintillis, meaning “five” in Latin, was the name of the 5th month used
Julius Caesar named it after himself.
5 (2) FOHRSDWUD, (3) Pompey, (4) Crassus
6 There is no reason, however, to believe that Caesar used these ciphers for long, or for
important messages. Cicero, with whom Caesar would have used the system, changed political
sides, making the system no longer secret. [ATTRIBUTION]
7 Seutonius: “When Augustus wrote in cipher he simply substituted the next letter of the
alphabet for the one required, except that he wrote AA for x” (the last letter of the Roman
alphabet). [Kahn, pg 84]