X509 certificate is one of many possible keys data object that can be
        associated with a key. Application may read and write X509 data
	from/to XML file. The X509 certificates management policies significantly
        vary from one crypto library to another. The examples in this chapter
        were tested with OpenSSL and they might be broken if anither crypto
	engine is used. Check API reference documentation for more specific 
        information about your crypto engine.