Verify signature in a Web browser

To verify a signature in a Web browser, follow these steps:

Server must obtain signed document

you can create file upload web page (look at this example code),
or you can perform verification after server completes the signature and saves the document on his hard disk.
We used this approach in our samples (Sign CreaDoc and Create simple signature).

Load xml document from file to MSXML XmlDOMDocument.
Create XmlSignature object.
Find signature node and attach it to XmlSignature object.
Verify the signature.
Validate the document.

<%
  ' load the document that was signed in browser
  Set doc = CreateObject("Msxml2.FreeThreadedDOMDocument.4.0")
  doc.preserveWhiteSpace=true ' Important!
  if not doc.load(Server.MapPath("uploaded.xml")) then Err.Raise 8, "" , doc.parseError.reason
    
  ' Create a signature object
  set cs = CreateObject("CreaSignClientIE.XmlSignature")

  ' Find the first signature in the document
  Set SignatureNode=doc.SelectSingleNode("//*[local-name(.)='Signature' and namespace-uri(.)='http://www.w3.org/2000/09/xmldsig#']")
  Set cs.XmlNode=SignatureNode


  set vr=cs.Verify(1)  ' 1 = do not check for revocation in demo version
  
%>

When the signature is invalid, the document should be rejected. The application should also implement additional checks to make sure that the document is valid. In this demo, we just print out the verification result and the document.

<table width="500px" border="0px" class="text">
  <tr>
    <td valign="top" align="left"> 
      <img src="<%if vr.OK then Response.Write("../images/signature_1.gif") else Response.Write("../images/signature_0.gif")%>">
    </td>
  </tr>
  <tr>
    <td>Signature OK:</td>
    <td class="value"><%= vr.OK %></font><td>
  </tr>
  <tr>
    <td width="120px">Signed by:</td>
    <td class="value"><%= vr.Signer.DisplayName %></td>
  </tr>
  <tr>
    <td width="120px">Issued by:</td>
    <td class="value"><%= vr.Signer.IssuerName %></td>
  </tr>
  <tr>
    <td valign="top">Error message:</td>
    <td class="value"><%= vr.ErrorMessage %></td>
  </tr>
</table>

See the demo in "Verify a Signature of a CreaDoc Document" for a detailed example of signature verification.

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