Q$3.$ In order to design a strong non$-$repudiation protocol a Trusted Third Party $($TTP$)$ is

generally required to provide:

Fairness

Proof Of Origin $($POO$)$

Proof Of Receipt $($POR$)$

Fig $3\mathrm{.}1$

a$)$

In the figure $3\mathrm{.}1,$ describe what is happening at each step, $1$ to $6?$

b$)$

Using the notation from the lectures describe step $1$ where the P$\_$POO is

provided.

Note: Data confidentiality is to be provided and the data sent is to be signed.

c$)$

Given the following message in a non$-$repudiation protocol:

i$)$ Explain what each part of this message is and what its primary function is$?$

ii$)$ Which step in the above diagram provides this message?