crypto-notes - Lecture Notes APPLIED CRYPTOGRAPHY AND DATA...

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Lecture Notes APPLIED CRYPTOGRAPHY AND DATA SECURITY (version 2.5 — January 2005) Prof. Christof Paar Chair for Communication Security Department of Electrical Engineering and Information Sciences Ruhr-Universit¨ at Bochum Germany www.crypto.rub.de
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Table of Contents 1 Introduction to Cryptography and Data Security 2 1.1 Literature Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2 Overview on the Field of Cryptology . . . . . . . . . . . . . . . . . . . . . . 4 1.3 Symmetric Cryptosystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.3.1 Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.3.2 A Motivating Example: The Substitution Cipher . . . . . . . . . . . 7 1.3.3 How Many Key Bits Are Enough? . . . . . . . . . . . . . . . . . . . . 9 1.4 Cryptanalysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.4.1 Rules of the Game . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.4.2 Attacks against Crypto Algorithms . . . . . . . . . . . . . . . . . . . 11 1.5 Some Number Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 1.6 Simple Blockciphers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 1.6.1 Shift Cipher . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 1.6.2 A±ne Cipher . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 1.7 Lessons Learned — Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 21 2 Stream Ciphers 22 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2.2 Some Remarks on Random Number Generators . . . . . . . . . . . . . . . . 26 2.3 General Thoughts on Security, One-Time Pad and Practical Stream Ciphers 27 2.4 Synchronous Stream Ciphers . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 i
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2.4.1 Linear Feedback Shift Registers (LFSR) . . . . . . . . . . . . . . . . 31 2.4.2 Clock Controlled Shift Registers . . . . . . . . . . . . . . . . . . . . . 34 2.5 Known Plaintext Attack Against Single LFSRs . . . . . . . . . . . . . . . . 35 2.6 Lessons Learned — Stream Ciphers . . . . . . . . . . . . . . . . . . . . . . . 37 3 Data Encryption Standard (DES) 38 3.1 Confusion and Di±usion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 3.2 Introduction to DES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 3.2.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 3.2.2 Permutations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 3.2.3 Core Iteration / f-Function . . . . . . . . . . . . . . . . . . . . . . . . 43 3.2.4 Key Schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 3.3 Decryption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 3.4 Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 3.4.1 Hardware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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crypto-notes - Lecture Notes APPLIED CRYPTOGRAPHY AND DATA...

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