You have the message sequence below.

Msg1. AS :{A, N1, Message1, h(A, N1, Message1)}{K1}

Msg2. SB :{A, N1, Message1, h(A, N1, Message1)}{K2}

Msg3. BA : B, N1, Message2, h(B, N1, Message2)

Whereas:

h(m) represents the digest of the message (m).

{m}{K} represents the encryption of message (m) using the key (K)

N1 is a random number.

1) What are the main objectives of the protocol. [ 5 Marks]

a) Define the roles of each participating party in the protocol

[ 2 Marks]

b) Based on your understanding of cryptographic systems, suggest approaches to share the keys K1 and K2.

[3 Marks]

2) Based on your understanding of the protocol above, explain the followings:

a) The reason why N1 is included in Msg3.

[2 Marks]

b) The reason why A is included in the digest calculation.

[3 Marks]

3) The protocol has a serious vulnerability, show the sequence of the message for this vulnerability and then explain the outcome of this vulnerability.

[10 Marks]

Question 1: You have the message sequence below. Msg1.A S:{A, N1, Message1, h(A, N1, Message 1)}{K1} Msg2. S-B:{A, N1, Message1, h(A, N1, Message1)}{K2} Msg3. B-A:B, N1, Message2, h(B, N1, Message2) Whereas: h(m) represents the digest of the message (m). {m}{K} represents the encryption of message (m) using the key (K) N1 is a random number. 1) What are the main objectives of the protocol. [ 5 Marks] a) Define the roles of each participating party in the protocol [2 marks] b) Based on your understanding of cryptographic systems, suggest approaches to share the keys K1 and K2 [3 Marks] 2) Based on your understanding of the protocol above, explain the followings: a) The reason why N1 is included in Msg3. [2 marks] b) The reason why "A" is included in the digest calculation. [3 Marks) 3) The protocol has a serious vulnerability, show the sequence of the message for this vulnerability and then explain the outcome of this vulnerability. [10 Marks)