DES - CSE 425, Introduction to Computer Security Chapter 5....

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CSE 425, Introduction to Computer Security Chapter 5. Cryptography. Data Encryption Standard (DES) © 2007 by Wayne R. Dyksen. All Rights Reserved. 5-1 Michigan State University Department of Computer Science and Engineering Cryptography and Network Security Chapter 3. Block Ciphers and the Data Encryption Standard by William Stallings Modern Cryptography Chapter 7.6. The Data Encryption Standard by Wenbo Mao Professor Wayne Dyksen Department of Computer Science and Engineering Michigan State University Spring 2007 CSE 425, Introduction to Computer Security 5-2 Cryptographic Systems Three Characteristics • Types of (E/D) Operations • Number of Keys • Number of Elements Per (E/D) Operation (E/D = Encryption/Decryption) (Element = Letter, Bit, Byte, Etc…) 5-3 Types of (E/D) Operations • Two Fundamental Operations – Substitution • Map One Element Into Another • E.g., a → B, b → C, c → D, etc… • Cryptoquote – Permutation (Transposition) • Rearrange Elements • E.g., 0 → 7, 1 → 3, 2 → 5, 3 → 0, 4 → 2, 5 → 6, 6 → 1, 7 → 4 • Word Scramble • Product Systems – Combination of Substitutions and Transpositions – Really “Composition” Systems 5-4 Substitution • Map One Element Into Another – E.g., a → B, b → C, c → D, etc… – Cryptoquote • Often… – Implemented as Table Lookup – Table Called “S-Box” (“Substitution-Box”) 1 0 14 4 13 1 2 15 11 8 3 10 6 12 5 9 0 7 0 1 1 0 0 0 1 0 15 7 4 14 2 13 1 10 6 12 11 9 5 3 8 0 0 0 Row 2 4 1 14 8 13 6 2 11 15 12 9 7 3 10 5 0 1 1 0 0 12 Column 3 15 12 8 2 4 9 1 7 5 11 3 14 10 0 6 13 5 S Box 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0101 Bits 1 to 6 S Box 5-5 Number of Keys • One Key – Same Key for Encryption and Decryption – AKA • Symmetric • Single-Key • Secret-Key • Two Keys – Separate Keys for Encryption and Decryption – AKA • Asymmetric • Two-Key • Public-Key 5-6 # of Elements Per (E/D) Operation • Stream Cipher – One Element • Letter • Bit • Byte • Etc… – Processed As a “Stream” • Block Cipher – N Elements At A Time • Letter • Bit • Byte • Etc… – Processed In “Blocks”
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CSE 425, Introduction to Computer Security Chapter 5. Cryptography. Data Encryption Standard (DES) © 2007 by Wayne R. Dyksen. All Rights Reserved. 5-2 Michigan State University Department of Computer Science and Engineering 5-7 Modern Encryption Scheme Substitution(s) and/or Transpositions(s) plaintext Substitution(s) and/or Permutation(s) : : Substitution(s) and/or Permutation(s) CIPHERTEXT Key(s)? Key(s)?
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This note was uploaded on 07/25/2008 for the course CSE 331 taught by Professor M.mccullen during the Spring '08 term at Michigan State University.

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DES - CSE 425, Introduction to Computer Security Chapter 5....

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