$13\mathrm{.}4.$ This exercise considers the security of key establishments with the aid of a KDC$.$ Assume that a hacker performs a successful attack against the KDC at the point of time tx$,$ where all keys are compromised. The attack is detected.$1.$ Which $($practical$)$ measures have to be taken in order to prevent decryption of future communication between the network nodes? $35413$ Key Establishment$2.$ Which steps did the attacker have to take in order to decipher data transmissions which occurred at an earlier time $($t $<$ tx$)?$ Does such a KDC system provide Perfect Forward Secrecy $($PFS$)$ or not?