Read the selection and answer the question.

Caesar Cipher

The field of cryptography can be traced back to Julius Caesar in the first century BC$.$ Now referred to as "Caesar Cipher," this early method of message encryption simply substituted one letter of the alphabet for another. These substitutions were made according to a chosen "shift." For example, using a shift of one, the letter A becomes B$,$ B becomes C$,$ C becomes D$,$ etc. The first documented use of Caesar Cipher displayed a shift of three. Of course, with only twenty$-$six potential shifts, Caesar Cipher was a very easy code to break, and over time, the technique became more associated with child's play than serious security. A good example of this demotion can be seen in the film A Christmas Story, where the young character of Ralphie eagerly uses his decoder ring to break a secret message from Little Orphan Annie. To his dismay, the secret message$$Drink More Ovaltine$$turns out to be entirely commercially motivated.

On the other hand, there is one form of Caesar Cipher that continues to live on$.$ Known as "rot$13,"$ this formula uses a shift of thirteen to convert plaintext $($readable text$)$ to ciphertext. Because the English language has twenty$-$six letters, a shift of thirteen is symmetrical, and in the computer world, the same command can be used to encrypt and decrypt information. Thus, for early computer users in the $1980$s$,$ rot$13$ became an easy way to communicate in code$$a practice that was often used in online forums to bypass language censorship. Frequent users even learned to read and write in rot$13$ as if it was a second language.

Using rot$13,$ the letter A would become $$

A

B$.$

B

M$.$

C

N$.$

D

Z$.$