From Basic Principles of Java and Internet Security CPS616 Web Technologies -- Spring 98. byGeoffrey C. Fox
A Digital ID typically contains the:
Owner's public key
Owner's name
Expiration date of the public key
Name of the issuer (the CA that issued the Digital ID)
Serial number of the Digital ID
Digital signature of the issuer
The most widely accepted format for Digital IDs is defined by the CCITT X.509 international standard; thus certificates can be read or written by any application complying with X.509.
Further refinements are found in the PKCS standards and the PEM standard.