Best known and one of the simplest polyalphabetic substitution ciphers
In this scheme the set of related monoalphabetic substitution rules consists of the 26 Caesar ciphers with shifts of 0 through 25
Each cipher is denoted by a key letter which is the ciphertext letter that substitutes for the plaintext letter a
To Encrypt: Ci = (pi + ki mod 26 ) mod 26
To Decrypt: pi = (ci - ki mod 26 ) mod 26
