tailieunhanh - Chapter 6: Lecture Data Encryption Standard (DES)

Objectives of Chapter 6: To review a short history of DES; to define the basic structure of DES; to describe the details of building elements of DES; to describe the round keys generation process; to analyze DES. | Chapter 6 Objectives Lecture Data Encryption Standard DES To review a short history of DES To define the basic structure of DES To describe the details of building elements of DES To describe the round keys generation process To analyze DES 6-1 INTRODUCTION History The Data Encryption Standard DES is a symmetric-key block cipher published by the National Institute of Standards and Technology NIST . In 1973 NIST published a request for proposals for a national symmetric-key cryptosystem. A proposal from IBM a modification of a project called Lucifer was accepted as DES. DES was published in the Federal Register in March 1975 as a draft of the Federal Information Processing Standard FIPS . Topics discussed in this section History Overview DES History in 1973 NIST then NBS issued request for proposals for a national cipher standard IBM already developed Lucifer cipher by team led by Feistel in late 60 s used 64-bit data blocks with 128-bit key 1974 IBM submits Lucifer Lucifer is analyzed and redesigned by NSA and others and becomes DES 1977 the new cryptosystem becomes the federal standard in USA till Nov. 2001 . Some variants of DES we ll discuss them later still very much in use. 1 DES Basic Principles DES is based on the Feistel Structure Feistel structure decrypt ciphertext is very similar to encrypt plaintext Uses the idea of a product cipher - that is a sequence of transformations The smaller transformations are substitutions and permutations 6-2 DES STRUCTURE The encryption process is made of two permutations P-boxes which we call initial and final permutations and sixteen Feistel rounds. Topics discussed in this section Initial and Final Permutations Rounds Cipher and Reverse Cipher Examples 6-2 Continue DES Encryption Overview Figure General structure of DES Continue Table Initial and final permutation tables Initial Permutation Final Permutation 58 50 42 34 26 18 10 02 60 52 44 36 28 20 12 04 62 54