We call a communication channel secure if it ensures the authenticity and the integrity of the

messages it transmits. Note that a secure communication channel does not ensure confidentiality. We call a communication channel private if it is secure and protect confidentiality.

We would like to establish a private channel based on a secure one.

1. How to do this by using standard cryptographic primitives?

2. We consider the Diffie-Hellman protocol. We assume that p and g are some standard numbers, where p is a prime number, agreed and safely stored by Alice and Bob. Recall how the Diffie-Hellman protocol works between Alice and Bob over a secure channel.

3. What can happen if the channel is no longer secure, i.e., if an adversary can tamper with the communication between Alice and Bob? Describe an attack.