Verify Digital Certificate

Hi,
I would like to verify the authenticity of a X509 digital certificate. I'm using Crypt::X509 to create a certificate object and can extract the data fields. But, I can't find a way to verify that the data has not been tampered with.
Is there a module I can use for this?
I have a copy of the public certificate used to sign the certificate I want to verify, but can't find the right code to call.

Thanks,
Clay