Caesar Cipher (The Beginning)

We are hopeful that this column is the beginning of a long and fruitful relationship with the children (whatever the relationship) of our faithful Krewe who wish to pass this fun hobby along to another generation. We also wish for this column to be useful to all of those Young at Heart aspirants interested in developing or fine tuning their solving techniques.

Let’s begin this first column with a brief explanation of the use of the term NOM by our ACA membership Krewe. NOM is short for Nom de Plume (from the French language meaning, “name of the pen” or “pen name”). ACA Krewe use NOMS to address one another while retaining their anonymity. This informality allows us to interact with each other as equals uncaring of one another’s position in life — doctor, lawyer or Indian Chief. Upon registration we ask you to list the first three choices of your personal NOM. This is because once a NOM has been registered with the ACA it may never be selected again.

Caesar’s Cipher

One way for someone new to cryptography to become acquainted with the substitution of one letter for another (simple substitution) is through the Caesar Cipher.

Julius Caesar (100 BC to 44 BC), Roman General, statesman and historian invented this simple cipher which still bears his name. To disguise his communications, he would shift  letters so many to the right or left for each message, producing a garbled looking mass of words which we call ciphertext, disguised letters or a system of visible secret writing.

Plaintext:  efghijklmnopqrstuvwxyzabcd
CIPHERTEXT: ABCDEFGHIJKLMNOPQRSTUVWXYZ

This alphabet has been shifted four letters. Plaintext is the original message before any encipherment (disguising) has taken place. To eliminate any confusion between plaintext and CIPHERTEXT letters, write plaintext letters in lower case letters and CIPHERTEXT letters in UPPER CASE letters.

Someone using this Caesar Cipher shift of four letters to send the message, “I will be there at four o’clock,” would simply substitute the CIPHERTEXT letters beneath the plaintext alphabet letters of the original message.

"I will be there at four o'clock."
"E SEHH XA PDANA WP BKQN K'YHKYG."

Do you see how this was done?

Unravel the disguised messages below. You will perform your first decipherment (conversion of disguised text to original text). Hint: Each message below has a Caesar Shift of four letters.

Caesar Ciphers (1)

K1. YNULPKCNWLDU   EO   BQJ.

K2. WYW   IAIXANO   WNA   YWHHAZ   GNASA.

K3. JKIO   WNA   WYW   YKZA   JWIAO.

K4. OAJZ   EJ   UKQN   OKHO.

Julius Caesar may have been a great soldier and conqueror, but when it comes to ciphers, he holds no better than the rank of lead-off novice in our Kiddee Korner cryptography lessons.

His ciphers (disguised messages) could be solved with a simple shift of letters between the plaintext (original message) alphabet and the CIPHERTEXT (disguised message) alphabet.

In our introduction to the Caesar Cipher, we looked at cipher messages constructed on the basis of the same shift of four letters between the plaintext and CIPHERTEXT alphabets. To increase the complexity of the disguise of a Caesar Cipher and to complicate its decipherment (changing disguised text to original text), shifts of one to twenty-five letters can be used to construct the disguised message. (Why can’t we shift twenty-six letters?)

Important note: Once the amount of the letter shift has been decided, the same number of shifts must be used for each letter in the cipher. Changing the number of the letter shift from letter to letter will make it unintelligible.

Each cipher below has been constructed with a different amount of letter shifts between the plaintext and the CIPHERTEXT. You must determine the amount of the shift for each cipher problem. Remember that the letter shifts must remain the same for each message.

A Caesar Alphabet Table appears below to help you change CIPHERTEXT to plaintext. To solve a Caesar Cipher “run down the alphabet table” with one of the CIPHERTEXT words until you find an intelligible plaintext word. You will then know the amount of letter shifts used for the rest of the message.

CAESAR Alphabet Table

   A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
 1 b c d e f g h i j k l m n o p q r s t u v w x y z a
 2 c d e f g h i j k l m n o p q r s t u v w x y z a b
 3 d e f g h i j k l m n o p q r s t u v w x y z a b c
 4 e f g h i j k l m n o p q r s t u v w x y z a b c d
 5 f g h i j k l m n o p q r s t u v w x y z a b c d e
 6 g h i j k l m n o p q r s t u v w x y z a b c d e f
 7 h i j k l m n o p q r s t u v w x y z a b c d e f g
 8 i j k l m n o p q r s t u v w x y z a b c d e f g h
 9 j k l m n o p q r s t u v w x y z a b c d e f g h i
10 k l m n o p q r s t u v w x y z a b c d e f g h i j
11 l m n o p q r s t u v w x y z a b c d e f g h i j k
12 m n o p q r s t u v w x y z a b c d e f g h i j k l
13 n o p q r s t u v w x y z a b c d e f g h i j k l m
14 o p q r s t u v w x y z a b c d e f g h i j k l m n
15 p q r s t u v w x y z a b c d e f g h i j k l m n o
16 q r s t u v w x y z a b c d e f g h i j k l m n o p
17 r s t u v w x y z a b c d e f g h i j k l m n o p q
18 s t u v w x y z a b c d e f g h i j k l m n o p q r
19 t u v w x y z a b c d e f g h i j k l m n o p q r s
20 u v w x y z a b c d e f g h i j k l m n o p q r s t
21 v w x y z a b c d e f g h i j k l m n o p q r s t u
22 w x y z a b c d e f g h i j k l m n o p q r s t u v
23 x y z a b c d e f g h i j k l m n o p q r s t u v w
24 y z a b c d e f g h i j k l m n o p q r s t u v w x
25 z a b c d e f g h i j k l m n o p q r s t u v w x y

Ciphertext Letters ZXBPXO
Ciphertext Letter shift – 1 aycqyp
No intelligible word here

Ciphertext Letter shift – 2 bzdrzq
No intelligible word here.

Ciphertext Letter shift – 3 caesar
Looks like a word to start Cipher K1 below.

Caesar Ciphers (2)

K1. ZXBPXO   ZFMEBOP   XOB   BXPV.

K2. UFJBUVYN NUVFY BYFJM MIFPCHA.

K3. HKKG BKN EJPAHHECEXHA SKNZ.

K4. PCEGQRCP GL RFC IGBBCC IPCUC. 

Parade of Cryptologists

It did not take long for Julius Caesar’s adversaries to unravel his Caesar shift foundation of secret messages and with the unraveling, began the 2000 year battle of wits, still alive and well today, between the cryptographers (writers of secret messages) and the cryptanalysts (decipherers of secret messages).

Distinctive list of renowned cryptologists

Simple Substitution Cipher

Caesar’s cryptic messaging with a simple alphabet shift soon became obvious to the least experienced cipher analysts. A fresh approach was needed. The world of the simple substitution cipher was born and letters were randomly chosen to depict other letters of the alphabet. Randomly selecting a cipher letter to represent another letter (plaintext letter) revoked the ease of simply looking for the number of shifts that a letter had been moved.

Simple substitution ciphertext is limited only by the ingenuity of the constructor (cryptographer). Its foundation may lie in an everyday medium found in the home, at work, at play or on the street. A telephone dial, computer keyboard, tic tac toe template, newspaper, book, compass, or simple street address may be the basis of ciphertext.