Chapter Summary

This chapter provides an overview of the problems that cryptology deals with. The first and oldest cryptographic primitive is encryption for secure transmission of messages. Some other primitives are key exchange, digital signature, authentication, secret sharing, hashing, and digital certificates. We then highlight the difference between symmetric (secret-key) and asymmetric (public-key) cryptography. The relevance of some computationally intractable mathematical problems in public-key cryptography is discussed next, and the working of a prototype public-key cryptosystem (RSA) is explained. We finally discuss different models of attacks on cryptosystems.

Not uncommonly, some people think that cryptology also deals with intrusion, viruses, and Trojan horses. We emphasize that this is never the case. Data and network security is the branch that deals with these topics. Cryptography is also a part of this branch, but not conversely. Imagine that your house is to be secured against theft. First, you need a good lock—that is, cryptography. However, a lock has nothing to prevent a thief from entering the house after breaking the window panes. A bad butler who leaks secret information of the house to the outside world also does not come under the jurisdiction of the lock. Securing your house requires adopting sufficient guards against all these possibilities of theft. In this book, we will study only the technology of manufacturing and breaking locks.