(a) Which PKI (Public Key Infrastructure) model is typically favored by business organization?

(b) Give one possible use of the "extensions" field of an X.509 certificate.

(c) Users in a PKI can obtain digital certificates of users they want to communicate with. Which protocol is typically used to interact with the directory server to obtain certificate(s)?

(d) Calculate the RSA public and private keys given the values of p and q as follows: p = 17; q = 11. Show details of workings.

Choose e = 7

(e) What is meant by Certificate Revocation? When would a certificate have to be revoked?

(f) Alice and Bob are communicating.

i. Explain how Alice and Bob can communicate such that all their communication can be authenticated and can be verified for integrity.

Confidentiality is not required.

ii. Modify your answer such that now it also provides replay attack detection.