15-CaesarCipher

Caesar Cipher

Introduction

Julius Caesar protected his confidential information by encrypting it using a cipher. Caesar's cipher shifts each letter by a number of letters. If the shift takes you past the end of the alphabet, just rotate back to the front of the alphabet. In the case of a rotation by 3, w, x, y and z would map to z, a, b and c.

Original alphabet:      abcdefghijklmnopqrstuvwxyz
Alphabet rotated +3:    defghijklmnopqrstuvwxyzabc

Example

$s =$ There's-a-starman-waiting-in-the-sky

$k = n$

The alphabet is rotated by $3$, matching the mapping above. The encrypted string is Wkhuh'v-d-vwdupqdq-zdlwlqj-lq-vkh-vnb

Note: The cipher only encrypts letters; symbols, such as -, remain unencrypted.

Function Description

caesar_cipher has the following paramter(s):

• string s: cleartext
• int k: the alphabet rotation factor

Returns

string: the encrypted string

Sample Input

middle-Outz
2

Sample Output

okffng-Qwvb

Explanation

Original alphabet:      abcdefghijklmnopqrstuvwxyz
Alphabet rotated +2:    cdefghijklmnopqrstuvwxyzab

m -> o
i -> k
d -> f
d -> f
l -> n
e -> g
-    -
O -> Q
u -> w
t -> v
z -> b