Mathematical Background of Public Key Cryptography

Cryptography is, in the true sense of the word, a classic discipline: we find it in Mesopotamia and Caesar used it. Typically, the historical examples involve secret services and military. Information is exchanged amongst a limited community in which each member is to be trusted. Like Caesar’s chiffre these systems were entirely symmetric. Thus, the communicating parties needed to have a common key which is used to deand encrypt. The key exchange posed a problem (and gives a marvellous plot for spy-novels) but the number of people involved was rather bounded. This has changed dramatically because of electronic communication in public networks. Since