The standard for certificates used on internet is
X.509 is a widely used standard for defining digital certificates
An X.509 certificate is a digital certificate that uses the widely accepted international X.509 public key infrastructure (PKI) standard to verify that a public key belongs to the user, computer or service identity contained within the certificate.
An X.509 certificate contains information about the identity to which a certificate is issued and the identity that issued it.
see this http://searchsecurity.techtarget.com/definition/X509-certificate