# Caesar Cipher

Sep 19, 2022#dsa#algorithms

In cryptography, a Caesar cipher, also known as Caesarâ€™s cipher, the shift cipher, Caesarâ€™s code or Caesar shift, is one of the simplest and most widely known encryption techniques. It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet. For example, with a left shift of 3, D would be replaced by A, E would become B, and so on. The method is named after Julius Caesar, who used it in his private correspondence.

The transformation can be represented by aligning two alphabets; the cipher alphabet is the plain alphabet rotated left or right by some number of positions. For instance, here is a Caesar cipher using a left rotation of three places, equivalent to a right shift of 23 (the shift parameter is used as the key):

``````Plain:    ABCDEFGHIJKLMNOPQRSTUVWXYZ
Cipher:   XYZABCDEFGHIJKLMNOPQRSTUVW``````

When encrypting, a person looks up each letter of the message in the â€śplainâ€ť line and writes down the corresponding letter in the â€ścipherâ€ť line.

``````Plaintext:  THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG
Ciphertext: QEB NRFZH YOLTK CLU GRJMP LSBO QEB IXWV ALD``````

Complexity:

• Time: O(|n|)
• Space: O(|n|)

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