Lecture5 - LECTURE V Eastern Mediterranean University School of Computing and Technology ITEC 443 Cryptography and Network Security Modern Ciphers

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Unformatted text preview: LECTURE - V Eastern Mediterranean University School of Computing and Technology ITEC 443 Cryptography and Network Security Modern Ciphers • Block Ciphers – The message is broken into blocks, • Each of which is then encrypted • (Like a substitution on very big characters - 64-bits or more) Dr. E. Iscioglu Cryptography and Network Security 2 Block Ciphers • Modern block ciphers are widely used to provide encryption of quantities of information, – And/or a cryptographic checksum to ensure the contents have not been altered • We continue to use block ciphers because they are comparatively fast, – and because we know a fair amount about how to design them • DES (Data Encryption Standard) is one of the best example. Dr. E. Iscioglu Cryptography and Network Security 3 Data Encryption Standard (DES) • The most widely used private key (symmetric) private key (symmetric) block cipher, is the Data Encryption Standard (DES). • It was adopted in 1977 by the National Bureau of Standards as Federal Information Processing Standard 46 (FIPS PUB 46) (-for all data communications). • DES encrypts data in 64-bit blocks using a 56-bit key. • The DES enjoys widespread use. • It has also been the subject of much controversy Dr. E. Iscioglu Cryptography and Network Security 4 Data Encryption Standard (DES) • Key: 64 bit quantity=8-bit parity+56-bit key – Every 8 th bit is a parity bit (or Remaining 8 bits). – What is the key length of original DES? • Ans: 64 bit key • The same algorithm is used for decryption • 64 bit input, 64 bit output. Dr. E. Iscioglu Cryptography and Network Security 5 DES Encryption 64 bit M 64 bit C Key 56 bits DES History • In the late 1960s, IBM set up a research project in computer cryptography led by Horst Feistel. • The project concluded in 1971 with the development of the LUCIFER algorithm. • LUCIFER is a Feistel block cipher that operates on blocks of 64 bits, using a key size of 128 bits. • Because of the promising results produced by the LUCIFER project, IBM embarked on an effort, headed by Walter Tuchman and Carl Meyer, to develop a marketable commercial encryption product that ideally could be implemented on a single chip. Dr. E. Iscioglu Cryptography and Network Security 6 DES History • It involved not only IBM researchers but also outside consultants and technical advice from NSA. • The outcome of this effort was a refined version of LUCIFER that was more resistant to cryptanalysis but that had a reduced key size of 56 bits, to fit on a single chip. • In 1973, the National Bureau of Standards (NBS) issued a request for proposals for a national cipher standard. • IBM submitted the modified LUCIFER. It was by far the best algorithm proposed and was adopted in 1977 as the Data Encryption Standard....
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This note was uploaded on 08/01/2011 for the course ITEC 443 taught by Professor Wqe during the Spring '11 term at Eastern Mediterranean University.

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Lecture5 - LECTURE V Eastern Mediterranean University School of Computing and Technology ITEC 443 Cryptography and Network Security Modern Ciphers

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