Answer Happy

Question 21 (5 points) Consider the following simple authentication protocol with three messages: 1. 2. 3. Alice + Bob: I am Alice, R1 Bob → Alice: R2, H(K.R1) 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 Kis generated randomly and has sufficient length (e.g., 160 bits). Replay attack Message modification attack. Eavesdropping/password guessing attack Reflection attack (or parallel session attack)