Hi all,

Today I'm posting a sample which signs an XML with or without a certificate (PFX file) and verifies the signature, all that with .NET and its SignedXml class. I won't include in the sample the code that VS designer includes when I add the textboxes and buttons used in the code. I don't think that's needed to understand the code.

<SAMPLE>

Imports System.Xml

Imports System.Security

Imports System.Security.Cryptography

Imports System.Security.Cryptography.Xml

Imports System.Security.Cryptography.X509Certificates

Public Class Form1

    Inherits System.Windows.Forms.Form
#Region " Windows Form Designer generated code "
...
#End Region
    Private Sub SignButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles SignButton.Click
        ' Generate a signing key.

        '

        Dim Key As New RSACryptoServiceProvider
        ' Create a new XML document.

        '

        Dim doc As New XmlDocument
        ' Format using white spaces.

        '

        doc.PreserveWhitespace = True
        ' Load the passed XML.

        '

        doc.Load(TextBox2.Text)
        ' Create a SignedXml object.

        '

        Dim signedXml As New SignedXml(doc)
        ' Add the key to the SignedXml document.

        '

        signedXml.SigningKey = Key
        ' Create a reference to be signed.

        '

        Dim reference As New Reference

        reference.Uri = ""
        ' Add a transformation to the reference.

        '

        Dim trns As XmlDsigC14NTransform = New XmlDsigC14NTransform

        reference.AddTransform(trns)
        ' Add an enveloped transformation to the reference.

        '

        Dim env As New XmlDsigEnvelopedSignatureTransform

        reference.AddTransform(env)
        ' Add the reference to the SignedXml object.

        '

        signedXml.AddReference(reference)
        ' Add an RSAKeyValue KeyInfo (optional; helps recipient find key to validate).

        '

        Dim keyInfo As New KeyInfo

        keyInfo.AddClause(New RSAKeyValue(CType(Key, RSA)))

        signedXml.KeyInfo = keyInfo
        ' Compute the signature.

        '

        signedXml.ComputeSignature()
        ' Get the XML representation of the signature and save

        ' it to an XmlElement object.

        '

        Dim xmlDigitalSignature As XmlElement = signedXml.GetXml()
        ' Append the element to the XML document.

        '

        doc.DocumentElement.AppendChild(doc.ImportNode(xmlDigitalSignature, True))
        If TypeOf doc.FirstChild Is XmlDeclaration Then

            doc.RemoveChild(doc.FirstChild)

        End If
        ' Show the signature

        '

        ToVerifyTextBox.Text = doc.OuterXml

    End Sub
    Private Sub SignWithCerButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles SignWithCerButton.Click
        ' Variables

        '

        Dim bResult As Boolean = False

        Dim pCertContext As IntPtr = IntPtr.Zero

        Dim key As RSA = Nothing

        Dim doc As XmlDocument = Nothing

        Dim signedXml As SignedXml = Nothing

        Dim reference As Reference = Nothing

        Dim trns As XmlDsigC14NTransform = Nothing

        Dim env As XmlDsigEnvelopedSignatureTransform = Nothing

        Dim keyInfo As KeyInfo = Nothing

        Dim xmlDigitalSignature As XmlElement = Nothing

        Dim cert As X509Certificate2 = Nothing

        Dim pass As SecureString = Nothing
        ' Generate a signing key from the subject certificate.

        '

        pass = New SecureString()

        pass.AppendChar("p")

        pass.AppendChar("a")

        pass.AppendChar("s")

        pass.AppendChar("s")

        pass.AppendChar("w")

        pass.AppendChar("o")

        pass.AppendChar("r")

        pass.AppendChar("d")

        cert = New X509Certificate2(TextBox1.Text, pass)

        key = cert.PrivateKey
        ' Create a new XML document.

        '

        doc = New XmlDocument
        ' Format using white spaces.

        '

        doc.PreserveWhitespace = True
        ' Load the passed XML.

        '

        doc.Load(TextBox2.Text)
        ' Create a SignedXml object.

        '

        signedXml = New SignedXml(doc)
        ' Add the key to the SignedXml document.

        '

        signedXml.SigningKey = key
        ' Create a reference to be signed.

        '

        reference = New Reference

        reference.Uri = ""
        ' Add a transformation to the reference.

        '

        trns = New XmlDsigC14NTransform

        reference.AddTransform(trns)
        ' Add an enveloped transformation to the reference.

        '

        env = New XmlDsigEnvelopedSignatureTransform

        reference.AddTransform(env)
        ' Add the reference to the SignedXml object.

        '

        signedXml.AddReference(reference)
        ' Add an RSAKeyValue KeyInfo (optional; helps recipient find key to validate).

        '

        'keyInfo = New KeyInfo

        'keyInfo.AddClause(New RSAKeyValue(CType(Key, RSA)))

        'signedXml.KeyInfo = keyInfo
        ' Create a new KeyInfo object.

        '

        keyInfo = New KeyInfo()
        ' Load the certificate into a KeyInfoX509Data object

        ' and add it to the KeyInfo object.

        keyInfo.AddClause(New KeyInfoX509Data(cert))
        ' Add the KeyInfo object to the SignedXml object.

        signedXml.KeyInfo = keyInfo
        ' Compute the signature.

        '

        signedXml.ComputeSignature()
        ' Get the XML representation of the signature and save

        ' it to an XmlElement object.

        '

        xmlDigitalSignature = signedXml.GetXml()
        ' Append the element to the XML document.

        '

        doc.DocumentElement.AppendChild(doc.ImportNode(xmlDigitalSignature, True))
        If TypeOf doc.FirstChild Is XmlDeclaration Then

            doc.RemoveChild(doc.FirstChild)

        End If
        ' Show the signature

        '

        ToVerifyTextBox.Text = doc.OuterXml
    End Sub
    Private Sub VerifyButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles VerifyButton.Click
        ' Create a new XML document.

        '

        Dim xmlDocument As New XmlDocument
        ' Format using white spaces.

        '

        xmlDocument.PreserveWhitespace = True
        ' Load the passed XML file into the document.

        '

        xmlDocument.LoadXml(ToVerifyTextBox.Text)
        ' Create a new SignedXml object and pass it the XML document class.

        '

        Dim signedXml As New SignedXml(xmlDocument)
        ' Find the "Signature" node and create a new XmlNodeList object.

        '

        Dim nodeList As XmlNodeList = xmlDocument.GetElementsByTagName("Signature", "http://www.w3.org/2000/09/xmldsig#")
        ' Load the signature node.

        '

        signedXml.LoadXml(CType(nodeList(0), XmlElement))
        ' Check the signature and show the result.

        '

        If signedXml.CheckSignature() Then

            MessageBox.Show("Signature verified!")

        Else

            MessageBox.Show("Invalid signature!!!")

        End If
    End Sub
End Class

</SAMPLE>

I hope this helps.

Cheers,

Alex (Alejandro Campos Magencio)