Answer Happy

Question 22 (5 points) Which of the following are valid solutions to fix the same protocol's vulnerability in the previous question? Include the sender's ID or IP address in the hash of the 2nd and 3rd message. Change both hashes into an AES encryption. Separate the second message into two messages, i.e., Bob send H(K, R1) to Alice first and then sends R2 next. A Adding a different constant number to the nonce in the hash of the 2nd and 3rd message.

Question 21 (5 points) Consider the following simple authentication protocol with three messages: 1. Alice + Bob: I am Alice, R1 2. Bob + Alice: R2, H(K, R1) 3. Alice + Bob: H (K, R2) where R1 and R2 are two randomly picked numbers, H is a cryptographic hashing function, and K is the shared secret between Alice and Bob. Which attack it is subjected to? Choose one (and explain it in your worksheet). Assume that the cryptographic primitives are secure. Secret key K is generated randomly and has sufficient length (e.g., 160 bits).