How to digitally sign XML document using Oracle 9i PL/SQL

Question

Let's say we have a simple XML document (doc.xml) like this:

<?xml version="1.0" encoding="UTF-8"?>
<Envelope xmlns="http://www.someexample.com/examples"&gt;
  <Salutation Id="test">
    Welcome!
  </Salutation>
</Envelope>

And a certificate file:test.p12

How to make a solution using Oracle 9i PL/SQL that digitally signs XML document according to http://www.w3.org/2000/09/xmldsig#

Any Digital Signature form (e.g. Enveloped) and method (e.g. RSAwithSHA1) example would be great.