X.509 certificate syntax

The current version of X.509 is 3, this are the fields:


1. version
2. serial number
3. signature algorithm ID
4. issuer name
5. validity period
6. subject (user) name
7. subject public key information
8. issuer unique identifier (version 2 and 3 only)
9. subject unique identifier (version 2 and 3 only)
10. extensions (version 3 only)
11. signature on the above fields

CISSP Exam can ask you about valid/invalid fields.

X.509 is supported by PEM, PKCS, S-HTTP, SSL, and other protocols

More info:
http://www.x5.net/faqs/crypto/q165.html