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Unformatted text preview: CS 161 Computer Security Spring 2010 Paxson/Wagner Notes 3/1 1 Brief History of Cryptography The word cryptography comes from the latin root crypt meaning secret, and graphia, meaning writing. So cryptography is literally the study of how to send secret messages. In the next few lectures we shall study encryption schemes as well as some other fundamental goals of cryptography: authentication and digital signatures. In a nutshell, cryptography is about communicating securely over an insecure communications medium. Schemes for sending secret messages go back to antiquity. The Romans used the Caesar cypher which consists of permuting the alphabet by simply shifting each letter forward by a fixed amount. For example, Caesar used a shift by 3 so the message cryptography would be encoded as fubswrjudskb. With the developement of the telegraph (wireless communication) at the end of the nineteenth century, the need for encryption in military and diplomatic communications became particularly important. The codes that were used during this pen and ink period were relatively simple since messages had to be decoded by hand. The codes were not very secure, especially given modern mathematical and statistical techniques. The second phase of cryptography, the mechanical era was the result of a German project to create a mechanical device for encrypting messages in an unbreakable code. The resulting Enigma machine was a remarkable engineering feat. Even more remarkable was the massive British effort to break the code. The breaking of the Enigma code was an important event that determined the course of World War II, and according to most experts shortened the war by about a year. There were three important factors in the breaking of the Enigma code. First, the British managed to obtain a replica of a working Enigma machine from Poland, which had cracked a simpler version of the code. The second factor was the sophistication of the Allied codebreakers, first the Poles, who employed a large contingent of mathematicians to crack the structure, and then the British, whose massive effort included Alan Turing, one of the founding fathers of computer science. The third factor was the scale of the code-breaking effort. The Germans figured that the Enigma was well-nigh uncrackable, but what they didnt figure on was the unprecedented level of commitment the British poured into breaking the Enigma, once the codebreakers made initial progress: at its peak, the British codebreaking organization employed over 10,000 people breaking these codes, a level of effort that vastly exceeded anything the Germans had anticipated. Modern cryptography is distinguished by its reliance on mathematics and electronic computers. It has its early roots in the work of Claude Shannon following World War II. The analysis of the one-time pad later in this lecture is due to Shannon. The early seventies saw the the introduction of the cryptosystem DES by NIST (the National Institute for Standards in Technology). DES answered the growing need for digital encryption(the National Institute for Standards in Technology)....
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This note was uploaded on 04/14/2010 for the course CS 161 taught by Professor Staff during the Spring '08 term at University of California, Berkeley.
- Spring '08
- Computer Security