CYSE476/ECE476 CRYPTOGRAPHY FUNDAMENTALS Project la: Analyze Historical Ciphers Reading Assignment: ● C. Paar and J. Pelzl, Understanding Cryptography, Chapter 1 • W. Stallings, Cryptography and Network Security 8th edition, Chapter

3 SPRING 2024 ● A. Menezes, P. van Oorschot, and S. Vanstone, Handbook of Applied Cryptography, Chapter 7.3 • CrypTool - Online Help Help → Starting page → Functionality of CrypTool → Document encryption → Sym- metric (classic) Help → Starting page → Functionality of CrypTool → Analyzing Documents → Tools for Analysis and Symmetric Encryption (classic) 1 Installation In order to complete this lab you might want to install CrypTool on your personal computer/laptop. You can download CrypTool from https://www.cryptool.org. The recommended version of software is CrypTool 1 (CT1) ver. 1.4.42 - English. 2 Frequency Analysis Task 1 (10 points) Prepare three relatively long English texts (each of the size of 10,000 or more letters) taken from: • novel, • newspaper, • reference manual. Find on the Internet a similar single text (≥ 10,000 letters) written in an arbitrary foreign language. • Determine and provide a histogram showing in the graphical form the relative frequency of letters in all four prepared long texts, as well, as the textual listings 26 most frequent diagrams and trigrams. • Do the frequency distributions depend significantly on the type of text in English? • Do these distributions depend significantly on the language in which the message was written? 1 CYSE476/ECE476 CRYPTOGRAPHY FUNDAMENTALS SPRING 2024 Task 2 (10 points) Take a small subset of all four texts prepared in Task 1, e.g., their first 200 letters, and recompute all frequency distributions. • Determine how good is the match between frequency distributions for short texts and long texts of the same type, written in the same language. • Summarize your observations. Task 3 (25 points) Encrypt a single long and a single short English text taken from a novel, prepared in Tasks 1 and 2, using the following 6 classical ciphers available in CrypTool: Caesar, Vigenere, Hill, Substitution, Playfair, and Permutation. Compute the frequency distribution of single letters, diagrams, and trigrams for all 12 obtained ciphertexts. . What are the characteristic features of the obtained distributions? • How you could use them to determine which cipher was used to obtain the given ciphertext? 2