In the following 3-way authentication protocol:
A -> B: $N_a$ || B || Signature_KprivA
B -> A: $N_a+1$ || $N_b$ || A || Signature_KprivB
A -> B: $N_b+1$ || Signature_KprivA
($N_a$ and $N_b$ are nonces, A and B are Alice and Bob, respectively)
How does the presence of the 3rd message remove the requirement to store nonces? In 3-way authentication, if there is no 3rd message, then the nonces must be stored and must have time stamps and the clocks must be synchronized.
I understand that the 3rd message is required for B to be sure that she is communicating with A and not with a MitM. However, in the presentation slides of my class, it's stated that without the 3rd message nonces must be stored-- but with it the nonces don´t need to be stored. Why is that?
