$.$ Mutual Authentication using Symmetric Key $[16$ Points$]$

$($a$)$ Consider the following mutual authentication protocol, where KAB is a shared

symmetric key.

Give two different attacks that Trudy can use to convince Bob that she is Alice.

$($b$)$ Consider the following protocol, where KAB is a shared symmetric key, CLNT and

SRVR are constants, and K $=$ h$($S$,$RA$,$RB$)$ is the session key.

$($i$)$ Does Alice authenticate Bob? Justify your answer.

$($ii$)$ Does Bob authenticate Alice? Justify your answer. Mutual Authentication using Symmetric Key $[16$ Points$]$

$($a$)$ Consider the following mutual authentication protocol, where $K_{AB}$ is a shared

symmetric key.

Give two different attacks that Trudy can use to convince Bob that she is Alice.

$($b$)$ Consider the following protocol, where KAB is a shared symmetric key, CLNT and

SRVR are constants, and $K=h(S,RA,RB)$ is the session key.

$($i$)$ Does Alice authenticate Bob? Justify your answer.

$($ii$)$ Does Bob authenticate Alice? Justify your answer.