You have the message sequence below.

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

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

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

Msg4: AB : {Data}{Ks}

Whereas:

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

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

PK is public key

N1 is a random number.

1. Explain the main objectives of the protocol.
2. Define the roles of each participating party in the protocol

[4 Marks]