Question:

(a) What is the use of digital certificate?

(b) What is meant by a hierarchical trust model in a Public Key Infrastructure? How does the Pretty Good Privacy (PGP) model of trust differ from this? Illustrate your answer with diagrams. Why is it important that PGP certificates allow multiple signers?

(c) What do you understand by certificate revocation? Give two instances when a certificate needs to be revoked. How does the public key infrastructure handle revocation?

(d) As a web user, how can you tell if the site you are communicating with is using SSL security?

(e) Explain how the dual signature used in the Secure Electronic Transaction (SET) protocol allows privacy, that is, the merchant can see only the order information and the bank can access only the payment information.

(f) Why is the 3-D secure protocol more secure than SET?