a$)$

An RSA cryptosystem uses $85$

as its modulus. What is the smallest composite number k

for which x$$xk

is a valid encryption function in this cryptosystem?

Score: $0/1$Unanswered

b$)$

Alf and Betty are setting up a Diffie$-$Hellman cryptosystem with prime modulus $97$

and primitive element $5$

$.$

Alf announces his encrypted number is $28$

$,$ and Betty announces her encrypted number is $91$

$.$

What is their shared secret key?