Alice and Bob want to exchange a secret key $k_{AB}$ using the following protocol.
Alice
$N_1$: random number
$c_1 = E_{k_{pub, B}}(ID_A||N_1)$
Bob
$c_1$
$ID_A, N_1 \leftarrow D_{k_{pr, B}}(c_1)$
$f(N_1) = N_1 + 1$
$N_2$: random number
$c_2 = E_{k_{pub, A}}(f(N_1)||N_2)$
$c_2$
$f(N_1), N_2 \leftarrow D_{k_{pr, A}}(c_2)$
$f(N_2) = N_2 + 1$
$c_3 = E_{k_{pub, B}}(f(N_2))$
Choose $k_{AB}$
$c_4 = E_{k_{pr, A}}(k_{AB})$
$c_5 = E_{k_{pub, B}}(c_4)$
$c_3$
$c_5$
The above protocol is not secure. Do you agree? Justify your answer. It is enough to sketch your attack against
this protocol, but not enough to give just the name of it.