Question: Security infrastructure and protocols

a. PKI and PGP are two methods for generating and managing public keys for use in protocols such as secure email. Compare and contrast the trust models for public keys used in PKI and PGP, and assess the statement that a PKI is a "topdown" approach to trust and PGP is a "bottom-up" approach to trust.

b. The SSL protocol uses (X.509) certificates to create a secure session between a server and a client in a web session. Discuss the browser-based trust model assumed in SSL, and compare it with the trust model used in Kerberos. Kerberos is designed to operate is a
relatively small domain, such as a single company. Discuss the practical issues around extending the Kerberos trust model to a global scale; say to provide secure services between Amazon and its customer base.
 
c.  Both IPsec and SSL provide encrypted network communication, but at different layers in the Internet protocol stack, and for different purposes. Compare and contrast these two protocols, and describe the secure communication scenarios they are best suited to address.
 
Tasks: 

a. Compare and contrast the trust models.

b. Compare and contrast the trust models; discuss details on implementing Kerberos on a large scale.

c. Compare and contrast the protocols; provide examples of best suited scenarios.