在linux上验证X.509证书

I have just started working with X.509 certificates. Can any one tell me how to go about validating a certificate on linux? The use case is that my app had downloaded a certificate in a previous session and I have to check if it is still valid (i.e., not expired or revoked since it was stored) before starting a new session. I understand a full sample will not be possible here, but any pointers will be useful.I have just started working with X.509 certific