Diffie$-$Hellman key exchange:

Start with the prime $p=17$ and the primitive root $g=3.$

$($a$)$ Alice chooses the secret key $a=4.$ Compute the public key

$A-=g^a,(modp)$

Alice sends $A$ to Bob.

$($b$)$ Bob chooses the secret key $b=5.$ Compute the public key

$B-=g^b,(modp)$

Bob sends $B$ to Alice.

$($c$)$ Use Diffie$-$Hellman key exchange to compute the secret key that Alice and Bob share.