1. Security and Applications (25 marks) a) [5 marks] Discuss the problems caused for firewalls by the use of VPNs and IPSec. b) [10 marks] Security services may be placed within each of the layers of the OSI reference model. List, describe, and discuss the advantages and layers. c) [10 marks] Both Alice and Bob have public-key capability. They wish to carry out mutual authentication. Let us assume that Alice and Bob already know each other's public keys. They want to establish a session, and then use symmetric session keys on that session, since it is typically 100 to 1000 times faster than public key cryptography. Write a protocol that enables Alice and Bob to mutually authenticate each other and agree on a shared secret key