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XmlDsigXPathTransform.XmlDsigXPathTransform Constructor

Initializes a new instance of the XmlDsigXPathTransform class.

Namespace: System.Security.Cryptography.Xml
Assembly: System.Security (in

public XmlDsigXPathTransform ()
public XmlDsigXPathTransform ()
public function XmlDsigXPathTransform ()
Not applicable.

The following code example shows how to sign and verify an XML document using the XmlDsigXPathTransform class. This example creates an envelope signature.

// This example signs an XML file using an
// envelope signature. It then verifies the 
// signed XML.
using System;
using System.Security.Cryptography;
using System.Security.Cryptography.X509Certificates;
using System.Security.Cryptography.Xml;
using System.Text;
using System.Xml;

public class SignVerifyEnvelope

    public static void Main(String[] args)
        // Generate a signing key.
        RSACryptoServiceProvider Key = new RSACryptoServiceProvider();

            // Create an XML file to sign.
            Console.WriteLine("New XML file created.");

            // Sign the XML that was just created and save it in a 
            // new file.
            SignXmlFile("Example.xml", "SignedExample.xml", Key, "ancestor-or-self::TempElement");
            Console.WriteLine("XML file signed.");

            // Verify the signature of the signed XML.
            Console.WriteLine("Verifying signature...");
            bool result = VerifyXmlFile("SignedExample.xml");

            // Display the results of the signature verification to \
            // the console.
            if (result)
                Console.WriteLine("The XML signature is valid.");
                Console.WriteLine("The XML signature is not valid.");
        catch (CryptographicException e)

    // Sign an XML file and save the signature in a new file.
    public static void SignXmlFile(string FileName, string SignedFileName, RSA Key, string XPathString)
        // Create a new XML document.
        XmlDocument doc = new XmlDocument();

        // Format the document to ignore white spaces.
        doc.PreserveWhitespace = false;

        // Load the passed XML file using it's name.
        doc.Load(new XmlTextReader(FileName));

        // Create a SignedXml object.
        SignedXml signedXml = new SignedXml(doc);

        // Add the key to the SignedXml document. 
        signedXml.SigningKey = Key;

        // Create a reference to be signed.
        Reference reference = new Reference();
        reference.Uri = "";

        // Create an XmlDsigXPathTransform object using 
        // the helper method 'CreateXPathTransform' defined
        // later in this sample.

        XmlDsigXPathTransform XPathTransform = CreateXPathTransform(XPathString);
        // Add the transform to the reference.

        // Add the reference to the SignedXml object.

        // Add an RSAKeyValue KeyInfo (optional; helps recipient find key to validate).
        KeyInfo keyInfo = new KeyInfo();
        keyInfo.AddClause(new RSAKeyValue((RSA)Key));
        signedXml.KeyInfo = keyInfo;

        // Compute the signature.

        // Get the XML representation of the signature and save
        // it to an XmlElement object.
        XmlElement xmlDigitalSignature = signedXml.GetXml();

        // Append the element to the XML document.
        doc.DocumentElement.AppendChild(doc.ImportNode(xmlDigitalSignature, true));

        // Save the signed XML document to a file specified
        // using the passed string.
        XmlTextWriter xmltw = new XmlTextWriter(SignedFileName, new UTF8Encoding(false));
    // Verify the signature of an XML file and return the result.
    public static Boolean VerifyXmlFile(String Name)
        // Create a new XML document.
        XmlDocument xmlDocument = new XmlDocument();

        // Format using white spaces.
        xmlDocument.PreserveWhitespace = true;

        // Load the passed XML file into the document. 

        // Create a new SignedXml object and pass it
        // the XML document class.
        SignedXml signedXml = new SignedXml(xmlDocument);

        // Find the "Signature" node and create a new
        // XmlNodeList object.
        XmlNodeList nodeList = xmlDocument.GetElementsByTagName("Signature");

        // Load the signature node.

        // Check the signature and return the result.
        return signedXml.CheckSignature();


    // Create the XML that represents the transform.
    private static XmlDsigXPathTransform CreateXPathTransform(string XPathString)
        // Create a new XMLDocument object.
        XmlDocument doc = new XmlDocument();

        // Create a new XmlElement.
        XmlElement xPathElem = doc.CreateElement("XPath");

        // Set the element text to the value
        // of the XPath string.
        xPathElem.InnerText = XPathString;

        // Create a new XmlDsigXPathTransform object.
        XmlDsigXPathTransform xForm = new XmlDsigXPathTransform();

        // Load the XPath XML from the element. 

        // Return the XML that represents the transform.
        return xForm;

    // Create example data to sign.
    public static void CreateSomeXml(string FileName)
        // Create a new XmlDocument object.
        XmlDocument document = new XmlDocument();

        // Create a new XmlNode object.
        XmlNode node = document.CreateNode(XmlNodeType.Element, "", "MyXML", "Don't_Sign");

        // Append the node to the document.

        // Create a new XmlNode object.
        XmlNode subnode = document.CreateNode(XmlNodeType.Element, "", "TempElement", "Sign");

        // Add some text to the node.
        subnode.InnerText = "Here is some data to sign.";

        // Append the node to the document.

        // Save the XML document to the file name specified.
        XmlTextWriter xmltw = new XmlTextWriter(FileName, new UTF8Encoding(false));

Windows 98, Windows Server 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0