ObjectReference


<ObjectReference IDREF="#timestamp" ; points to object
  Type="http://www.w3.org/1999/xmldsig-core/SignatureAttributes">
  <Transforms> ; source tree to output octect
     <Transform Algorithm="http://w3.org/1999/XPath"/>
     <Transform Algorithm="http://w3.org/1999/xmldsig-core/c14n"/>
   </Transforms>
  <DigestMethod Algorithm="http://w3.org/1999/xmldsig-core/sha1"/>
  <DigestValue>a53uud43</DigestValue>
</ObjectReference>