Definition:Caesar Cipher

Definition

A Caesar cipher is a substitution cipher in which each letter is replaced by another such letter a constant number of places along in the alphabet.

The alphabet is considered to be written in a circle, so that (for example, in the English alphabet) after $\texttt Z$ comes $\texttt A$.

Caesar Shift

Let $n$ be the constant number of places along in the alphabet by which a Caesar cipher encodes a plaintext message.

The constant $n$ is referred to as the Caesar shift.

Examples

Caesar Shift of $5$

A Caesar cipher on the English alphabet with a Caesar shift of $5$ can be depicted in two-row notation as:

$\texttt {A B C D E F G H I J K L M N O P Q R S T U V W X Y Z}$

$\texttt {F G H I J K L M N O P Q R S T U V W X Y Z A B C D E}$

Hence, for example:

$\texttt {A B Y}$

is encoded as:

$\texttt {F G D}$

Also see

• Definition:Substitution Cipher

• Results about Caesar ciphers can be found here.

Source of Name

This entry was named for Julius Caesar.

Historical Note

The Caesar cipher is one of the substitution ciphers described by Julius Caesar.

Sources

• 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): Caesar cipher