4.State T/F in the concept of kerberos, Emailand X.509for the following Statements:

a) Kerberos is susceptible to man-in-the-middle attacks:

b) In Kerberos all servers share a secret with the authentication server only clients and TGS shares a secret with the AS

c) The purpose of the authenticator in Kerberos is to avoid replay attacks

d) Kerberos requires time synchronization of all clients and servers to use time stamps

e) Reverse certificates are used for revocation of X.509 certificates

f) In Kerberos the ticket granting server shares a secret with the authentication server.

g) During the process of registration every entity who wishes to obtain a certificate from the CA should provide a copy of their private keys to the CA. 3

h) PGP requires an hierarchical certificate authority, No CA needed

i) The Key ID of a PGP key is the last 64 bits of the private key. last 64 bits of the public key

j) In the PGP private key ring of Joe, Joe's RSA private key is stored encrypted using the corresponding public key. encrypted using Joe's password