Key exchange$($a$)(1$pt$.)$ We saw that plain DH key exchange $($DHKE$)$ protocol is vulnerable$$against man$-$in$-$the$-$middle $($MITM$)$ attacks. Give a variant of$$the DHKE protocol that uses digital signatures and prevents MITM$$attacks$.($b$)(1$pt$.)$ Provide an alternative of the previous protocol to establish a$$new session key using KEMs and digital signatures.