Symmetric Ciphering

Shift and substitution ciphers have been used for written text transmission and dominated the art of secret writing for at least two millenniums (and maybe more). The most known historical ciphers in this category, include Caesar's, Vigenere's, affine, one‐time pad, and Enigma ciphers. With the advent of computers, shift and substitution ciphering were abandoned, because it has become easy to break them. However, it is important to learn them since they had inspired the modern cryptography. One of the most known shift ciphers is Caesar's cipher used in the Roman Empire to encrypt messages exchanged between Roma (i.e. the emperor and his attorneys) and roman armies around the world. At ancient Rome, the romans had an intelligence system comparable to the one in today's USA. To make attacks based on frequency analysis harder, polyalphabetic ciphers have been invented in the 16th century.