US encryption standard [NIST 1993] 56-bit symmetric key, 64-bit plaintext input. Modern Block Ciphers. E.g. AES currently widely deployed in banking, commerce and Web Data Encryption Standard (DES).ppt from CPIS 603 at University of Jeddah. Block Cipher Design. History of DES •1970s: Horst Feistel designs Lucifer at IBM key = 128 bits, block = 128 bits •1973: NBS asks for block cipher proposals. If input is larger than b bits it can be divided further. Block Cipher Design Principles. ICS 454: Principles of Cryptography Block Ciphers & DES Sultan Almuhammadi Outline Stream cipher vs. Block cipher Motivation Reversible vs. Irreversible mapping Ideal Block Cipher DES Stream Cipher & Block Cipher stream cipher: encrypts data stream one bit or one byte at a time. It uses 16 round Feistel structure. in a block cipher the message is broken into blocks, each of which is then encrypted (ie like a substitution on very big characters - 64-bits or more) most modern ciphers we will study are of this form Shannons Theory of Secrecy Systems. •1976: NBS adopts DES as federal standard key = 56 bits, block = 64 bits •1997: DES broken by exhaustive search •2000: NIST adopts Rijndael as AES to replace DES. CPIS 603 Cryptography Block Cipher and Data Encryption Standard 1 Block cipher and stream cipher • block ciphers. Typical block sizes are 64 or 128 bits Most of the ciphers are block ciphers. DoE(m) = m () Block vs Stream Ciphers Block Cipher Principles • many symmetric block ciphers are based on a Feistel Cipher Structure (more below) • Feistel makes it possible decrypt ciphertext efficiently to recover messages • block ciphers look like an extremely large substitution • for a 64 -bit block … DES is an implementation of a Feistel Cipher. Study Resources. Although much progress has been made in designing block ciphers that are cryptographically strong, the basic principles have not changed all that much since the work of Feistel and the DES design team in the early 1970s. no known good analytic attack. Block Ciphers. block cipher with cipher block chaining. Introduction to Block Ciphers A Block Cipher Algorithm: E and D are a pair of encryption and decryption operators that satisfy: ( ) , 2 (2) 2 ( ) E F 2 F F GF n → n = where m is an n-bit message, i.e., E maps a n-bit message to a n-bit cipher text. INTRODUCTION Block ciphers: Encrypts a block of plaintext as a whole to produce same sized ciphertext. IBM submits variant of Lucifer. DES Challenge: 56-bit-key-encrypted phrase decrypted (brute force) in less than a day. Symmetric key crypto: DES. The block size is 64-bit. Security: 8- DES: Data Encryption Standard. how secure is DES? Stream ciphers: Stream ciphers process messages a bit or byte at a time when en/decrypting Block cipher is an encryption algorithm which takes fixed size of input say b bits and produces a ciphertext of b bits again. A. DES 1. now look at modern block ciphers ; one of the most widely used types of cryptographic algorithms ; provide secrecy /authentication services ; focus on DES (Data Encryption Standard) to illustrate block cipher design principles; 4 Block vs Stream Ciphers. The Data Encryption Standard (DES) is a symmetric-key block cipher published by the National Institute of Standards and Technology (NIST). Encryption algorithms are divided into two categories based on input type, as block cipher and stream cipher. Principles Unit 2. Data Encryption Standard - DESDES was developed as a standard for communications and data protection by an IBM research team, in response to a public request for proposals by the NBS - the National Bureau of Standards (which is now known as NIST). 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