Substitution ciphers: Ancient - Renaissance

Cryptography is the process by which messages are communicated through secret means. Cipher cryptography converts messages by applying some cipher algorithm with a secret key to a plaintext message, converting it into a ciphertext message that cannot be read by interceptors. Cryptanalysis is the science that attempts to decipher these messages without access to the secret key. This talk focuses on substitution ciphers and demonstrates the processes of encrypting and breaking some examples of these. The focus is on the battle between cryptographers - who create cipher systems - and cryptanalysts - who attempt to break them. As cryptanalysis develops more ingenious ciphers must be created and this constant struggle evolves from Roman generals, through the Golden Age of Islam to political intrigue in Renaissance Europe. This talk provides a gentle introduction and assumes no prior knowledge of cryptography. An article on this topic, "Ciphers through the ages" by Peter Rowlett, appears in issue 10 of iSquared Magazine (Winter 2009/10), on pages 24-27. Find out more about the magazine and how to subscribe, buy the current issue or back copies of previous issues at the iSquared Magazine shop.