Cse 565 Computer Security Solution Key For Midterm 2

This study source was downloaded by 100000802832151 from CourseHero.com on 11-14-2022 03:06:49 GMT -06:00https://www.coursehero.com/file/21125136/Midterm2-solution-key/ 1 CSE 565 Computer Security Solution Key for Midterm 2 Question 1: 20 (3 + 7 + 6 + 4) points a) What are three broad categories of applications of public-key cryptosystem? Ans: Encryption/decryption: The sender encrypts a message with the recipient's public key. Digital signature: The sender "signs" a message with its private key. Signing is achieved by a cryptographic algorithm applied to the message or to a small block of data that is a function of the message. Key exchange: Two sides cooperate to exchange a session key. Several different approaches are possible, involving the private key(s) of one or both parties. b) In a public-key system using RSA, you intercept the ciphertext C = 10 sent to a user whose public key is e = 5, n = 35. What is the plaintext M? (This is a hacking exercise.) Ans: P = Cd mod 35. We need to first determine d. Eulers totient (35) = (p-1) x (q-1) = (7-1) x (5-1) = 24. e=5. Decryption key d is the inverse of e modulo 24. Therefore, d=5. 105 mod 35 = 102 x