ABSTRACT

In this chapter, the authors present a type of polyalphabetic cipher that was developed in the late 1500s by a Frenchman named Blaise de Vigenere. They describe Vigenere ciphers can be broken through a little perseverance and ingenuity. With a Vigenere cipher, for each plaintext character, the corresponding ciphertext character is the character in the Vigenere square where the column labeled with the plaintext character intersects the row labeled with the keyword character. The authors show how Maple can be used to encrypt and decrypt messages using Vigenere ciphers. They demonstrate how MATLAB can be used to encrypt and decrypt messages using Vigenere ciphers. The authors provide an example of successful cryptanalysis on a ciphertext formed using a Vigenere cipher. Shift and affine ciphers are examples of monoalphabetic ciphers, meaning that each occurrence of every possible plaintext character is replaced with the same ciphertext character.