Criptografia

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Chapter Overview of Cryptography
Contents in Brief

1.1 Introduction
Cryptography has a long and fascinating history. The most complete non-technical account of the subject is Kahn’s The Codebreakers. This book traces cryptography from its initial and limited use by the Egyptians some 4000 years ago, to the twentieth century where it played a crucial role in the outcome of both world wars.Completed in 1963, Kahn’s book covers those aspects of the history which were most significant (up to that time) to the development of the subject. The predominant practitioners of the art were those associated with the military, the diplomatic service and government in general. Cryptography was used as a tool to protect national secrets and strategies. The proliferation of computers and communicationssystems in the 1960s brought with it a demand from the private sector for means to protect information in digital form and to provide security services. Beginning with the work of Feistel at IBM in the early 1970s and culminating in 1977 with the adoption as a U.S. Federal Information Processing Standard for encrypting unclassified information, DES, the Data Encryption Standard, is the mostwell-known cryptographic mechanism in history. It remains the standard means for securing electronic commerce for many financial institutions around the world. The most striking development in the history of cryptography came in 1976 when Diffie and Hellman published New Directions in Cryptography. This paper introduced the revolutionary concept of public-key cryptography and also provided a new andingenious method 1

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1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 1.10 1.11 1.12 1.13 1.14

Introduction Information security and cryptography Background on functions Basic terminology and concepts Symmetric-key encryption Digital signatures Authentication and identification Public-key cryptography Hash functions Protocols and mechanisms Key establishment, management, and certification Pseudorandom numbers andsequences Classes of attacks and security models Notes and further references

1 2 6 11 15 22 24 25 33 33 35 39 41 45

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Ch. 1 Overview of Cryptography

for key exchange, the security of which is based on the intractability of the discrete logarithm problem. Although the authors had no practical realization of a public-key encryption scheme at the time, the idea was clear and it generatedextensive interest and activity in the cryptographic community. In 1978 Rivest, Shamir, and Adleman discovered the first practical public-key encryption and signature scheme, now referred to as RSA. The RSA scheme is based on another hard mathematical problem, the intractability of factoring large integers. This application of a hard mathematical problem to cryptography revitalized efforts to find moreefficient methods to factor. The 1980s saw major advances in this area but none which rendered the RSA system insecure. Another class of powerful and practical public-key schemes was found by ElGamal in 1985. These are also based on the discrete logarithm problem. One of the most significant contributions provided by public-key cryptography is the digital signature. In 1991 the first international...
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