title: X509Data element appearing twice in signature
body: <p>I am trying to decrypt (and later encrypt) an email message (ebXML). The message contains a Signature element that contains child elements to specify the SignedInfo, SignatureValue and KeyInfo. Also, the message contains an encrypted attachment.</p>
  
  <p>The KeyInfo element contains two X509Data elements. Each of these specify a X509Certificate. Why are there two certificates? Is it one certificate for the message itself and one certificate for the attachment?</p>