Using examples where appropriate, explain the following $($TLS$-$related$)$ terms:

$$ Forward secrecy

$$ OCSP Stapling

$$ Authenticated Encryption with Additional Data $($AEAD$)$

$[3$ marks$]$

b$)$ What is meant by port scanning? In your answer, use diagrams to explain $2$ scans

of your choice. Further on$,$ show how systems can be hardened against such scans.

$[4$ marks$]$

c$)$ Using an example explain how a simple substitution cipher can be broken via a

letter frequency distribution analysis.