X.509 Certificates

ITU-T recommendation X.509 is part of the X.500 series of recommendations that define a directory service. The directory is, in effect, a server or distributed set of servers that maintains a database of information about users. The information ­includes a mapping from user name to network address, as well as other attributes and information about the users.  For this discussion, please provide thorough responses to the following:

1) Describe the X.509 certificate and standard.

2) What is the purpose of the X.509 standard?

3) How is an X.509 certificate revoked?