Re: X509 data element

>    1. When X509 certificate element is present, is there any need
>       for X509IssuerSerial, X509SubjectName, X509SKI, elements. Is 
>       it possible for all of these to be present. If so, what is 
>       the significance of the later three, as the first one contains 
>       all of them.

Many implementations actually provide more than one of the differnet 
forms in the same signature.  Yes, the certificate includes all the 
other data, but it requires a fairly heavy-duty ASN1/DER parser. 
Breaking out the alternate "lookup keys" is just "friendly," as it were.

>    2. Also, how is a certificate validated. Is it by 

That's a local trust issue, and depends on your implementation and 
business requirements.  A common 80/20 technique is to verify that the 
certificate *or it's issuer* came from a locally-configured trusted list.

	/r$