The Local Certificate Authority (Local CA) integrates a basic certificate authority functionality on the security appliance, deploys certificates, and provides secure revocation checking of issued certificates. The Local CA provides trusted digital certificates to users, without the need to rely on external certificate authorization.
In order to configure PIX as a CA(LOCAL CA) you need to have the software version 8.x.Following link will help you in configuring the PIX as CA:
http://www.cisco.com/en/US/docs/security/asa/asa81/config/guide/cert_cfg.html#wp1067484
If you want to configure certificate in PIX check thw following url which contains more details about the same:
http://www.cisco.com/en/US/docs/security/asa/asa81/config/guide/cert_cfg.html#wp1002608
