Key exchange

$($a$)(1$pt$.)$ We saw that plain DH key exchange $($DHKE$)$ protocol is vul$-$

nerable 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.