803402 VO Kryptologie (2004W)

Cryptology is concerned with encoding of messages; it is in particular important for the security of worlwide computer networks. It serves the concealment of messages and signing documents as well. We distinguish
between symmetric and asymmetric cryptosystems. A typical examples of a
symmetric encryption which was used worldwide until 1997 was the DES
encryption system. As it was broken in 1997 it has meanwhile been replaced by the AES encryption system. From a mathematical point of view the asymmetric encryption systems are more interesting; in order to understand
how they work we need some knowledge from Number Theory. Secrecy of these systems is based on the fact that it is impossible to find the prime factorisation of large numbers in a reasonable timespan. For that reason we
will also be concerned with the question how large prime numbers can be found.