Block Cipher and the Data Encryption Standards
Outline 1. Block Cipher vs Stream Cipher 2. Block Cipher Designing Principles 3. Feistel Cipher 4. DES 1. Block Cipher and Stream Cipher 1.1 Block Cipher : In which a block of plaintext is treated as a whole and used to produce a ciphertext block of equal length. Typically a block size of 64 bit or 128 bits is used. Fig. 1. Block Cipher 1.2 Stream Cipher : In which data is encrypted one bit at a time. Fig. 2. Stream Cipher 2. Block Cipher Design Principles The main principles are defined below. This will be more cleared once you will study DES and Feistel Cipher. 2.1 No. of Rounds : Greater the Number of rounds greater will be the difficulty to break. Generally, 16 rounds are considered. Note 1. Schneier observes that for 16 rounds DES, a differential cryptanalysis attach require 2^(55.1) operations whereas, Brute force requires 2^(55) operations. so if DES has 15 or less than 15 rounds differential cryptanalysis requires less effort that brute force. Different...