Cryptology is the science of coding and decoding secret messages. (Crypto is the Greek root for secret or hidden). It is usually divided into Cryptography, which concerns designing cryptosystems for coding and decoding messages, and the more glamorous Cryptanalysis, which is concerned with ``breaking'' cryptosystems, or deciphering messages without prior detailed knowledge of the cryptosystem.
You might think the world would be a lot better if we all got along and communicated openly with one another, but it has been an unfortunate fact since time began that there have been lots of reasons for desiring secure communication. The twentieth century has seen a dramatic increase in the need for secure communications in matters of politics, commerce, and even in social communication, as more and more of us depend on electronic mail and other computer-based forms of communication.
It is very simple for any organization that provides access to electronic mail to monitor the messages that are sent. Already, this has generated many contentious situations based on companies and schools monitoring the computer activities and messages of their employees and students, respectively.
Modern cryptology is based on ideas from theoretical computer science and increasingly Number Theory (the mathematics of integers). Startlingly simple ideas in number theory have formed the basis of unbelievably secure and flexible cryptosystems. The logo on the lecture announcement is that of RSA Data Security, Inc. a monstrous company founded by one computer scientist (Adi Shamir) and two number theorists (Rivest and Adleman) who basically were in the right place at the right time. There is now a ``gold rush'' of number theorists trying to exploit modern number theory to design and break cryptosystems. For that reason, the National Security Agency (the nation's largest employer of mathematicians) supports research across the nation in any form of number theory. More than half a dozen of the faculty in the math department at O.S.U. are currently or have been supported by the NSA.