Computer Security and Cryptography

WHY STUDY CRYPTOGRAPHY?

There is a symbiotic relationship between cryptography and the development of highperformance computing systems. Modern-day computers were created at the behest of twentieth-century cryptanalysts. As the complexity of cryptographic systems progressed from mechanical to electronic systems, so did the need to develop more efficient methods to cryptanalyze them.

Every cryptosystem, which has a finite number of keys, can usually be analyzed by key trial, deciphering the ciphertext with all possible keys until some recognizable text appears. In many “classical” cryptographic systems, the testing of keys could be performed by hand. The stimulus for the development of computers was the need to be able to test large sets of possible keys to decipher coded traffic. Modern cryptosystems are such that the number of possible keys is generally so large as to make exhaustive key trial infeasible. Even computers are limited, and some analysis must precede key testing for the process to be successful.

The marriage of computing and cryptography provides a marvelous real-life application of mathematics, and develops the inference skills that are fundamental to engineering and science. When a student first views the ciphertext

     To-drijohrunurmanpmlgchd-ehapuotp,te-nmabsno-nitioippmbo-a-a
     sTasm-h-op-ms-vye-m.ikndu-n-atscegnetoin-l-rs-v-e-u-ta-olati
     s-t-sccw—eorrgdhgngP.r-stenvercenhnerhchoie-nun-sr-tois-rma
     eaeeadadrssou-o-etat-iefeotifc-m-a—ergua-eiuo-oixeordalmyes

there ...