Caesar cipher, the most widely known encryption technique
Caesar cipher replaces each letter in a text is by a letter a fixed number of places down the alphabet.
Overview
Caesar cipher is a simple substitution cipher. It rotates the plaintext alphabet by a fixed number of places. The latter is called the “shift” and forms the key of this cipher.
Plaintext: abcdefghijklmnopqrstuvwxyz Ciphertext: defghijklmnopqrstuvwxyzabc
Example
Assuming the Latin alphabet and a shift of 3 we would replace A with D, B with E, …, Y with B, and Z with C. Try it with the plaintext ciphereditor. You should get the ciphertext jpwolylkpavy.
How to break the cipher?
The Caesar cipher can be easily broken in a ciphertext-only scenario.
The shift is the key to this cipher and may take up to 25 possible values (assuming the Latin alphabet A-Z with 26 characters). Any other shift value is equivalent to the shift value you get by dividing by the number of characters in the alphabet and taking the remainder (the “modulo operation”). Thus, 260.003 is equivalent to shift 3.
You may break the cipher in a brute-force attack by deciphering the ciphertext at hand using all possible shift values and choosing the original text among them. The latter can be done intuitively or automatically using a dictionary or statistical manners (e.g. frequency analysis).