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1. Conceptual questions (only one-line answer) a. What is the main application of cryptography? b. DES has a small key, what is another major problem? C. What are the final nodes in an attack tree represent? d. All reachable and exploitable vulnerabilities in a system are commonly referred as: e. Which cipher is more difficult to break using frequency analysis: monoalphabetic, playfair, vigenere? f. A small change in either the plaintext or the key should produce a significant change in the ciphertext. What is this property called? 8. Give an example of: (1) computationally secure cipher; (2) unconditionally secure cpher. h. DES has 16 rounds. i. What is the problem if it has more rounds? ii. What is the problem if it has fewer rounds? 1. How many round keys are needed for AES with 256-bit key