Consider a one$-$way authentication technique based on asymmetric encryption $($PUa is A$$s public key$)$:

A $->$ B:IDA

B $->$ A:E$($PUa$,$R$2)$ A $->$ B:R$2$

$($a$)$ Explain the protocol.

$($b$)$ What type of attack is this protocol susceptible to$?$