Visual Basic Source: verify.frm

Dim xmldoc As New DOMDocument50
Dim xmldsig As New MXDigitalSignature50
Dim dsigKey As IXMLDSigKey
Dim dataObj As IXMLDOMNode

Const DSIGNS = "xmlns:ds='http://www.w3.org/2000/09/xmldsig#'"
Const INFILE = "signature.verify.dsa.xml"

Private Function WriteLine(ByVal str As String)
    Text1.Text = Text1.Text + str + vbNewLine
End Function
Private Function writeClear()
    Text1.Text = ""
End Function

Private Function LoadXML(ByVal file As String)
    ' Read input xml file and display the content in the text1.
    Path = App.Path + "\" + file
    xmldoc.async = False
    xmldoc.preserveWhiteSpace = True
    xmldoc.validateOnParse = False
    xmldoc.resolveExternals = False
    If xmldoc.Load(Path) = False Then
        WriteLine "Can't load " + Path
        WriteLine "Reason: " + xmldoc.parseError.reason
        LoadXML = False
        Exit Function
    End If
    xmldoc.setProperty "SelectionNamespaces", DSIGNS
    Set xmldsig.signature = xmldoc.selectSingleNode(".//ds:Signature")
    LoadXML = True
End Function


Private Function VerifyXML()
    If xmldsig.signature Is Nothing Then
        WriteLine "Invalid signature."
        VerifyXML = False
        Exit Function
    End If
    
    Set oKeyInfo = xmldoc.selectSingleNode(".//ds:KeyInfo/ds:KeyValue")
    If oKeyInfo Is Nothing Then
        WriteLine "Invalid <KeyInfo> element."
        VerifyXML = False
        Exit Function
    End If
    
    Set oPubKey = xmldsig.createKeyFromNode(oKeyInfo)
    If oPubKey Is Nothing Then
        WriteLine "Can't generate public key for verification."
        VerifyXML = False
        Exit Function
    End If
    
    Set oVerifiedKey = xmldsig.verify(oPubKey)
    If oVerifiedKey Is Nothing Then
        WriteLine "Signature not verified."
    End If
       
    WriteLine "Signature verified."
    VerifyXML = True
End Function

Private Sub Form_Load()
    
    writeClear
    WriteLine "Verifyin signature."
    If LoadXML(INFILE) = True Then
        VerifyXML
    End If
End Sub

Try It!

1. Ensure that you have completed all the procedures in Getting Started with XML Digital Signatures.
2. Copy the XML signature resource file, and paste it into a text file. Save the file as signature.verify.dsa.xml.
3. Create a Standard EXE project in Visual Basic. Save the empty project as verify.vbp to the same directory where you saved signature.verify.dsa.xml. Name the form file verify.frm.
4. Create a reference to MSXML 5.0. To do this, select References... from the Project menu, then check the box for Microsoft XML, v5.0.
5. Copy the Visual Basic code listing above, and paste it into the code editor to replace whatever is already there.
6. Place a TextBox control onto the form. It should be named as Text1 (the default name). Click it to select it in the Properties window, and then modify the following properties for Text1: set the ScrollBars property to "2 – Vertical" and the MultiLine Property to True.
7. Execute the code by selecting Start from the Run menu.
8. Verify that the output is the same as that listed in the Output topic.