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XmlDsigXPathTransform Class

Represents the XPath transform for a digital signature as defined by the W3C.

Namespace: System.Security.Cryptography.Xml
Assembly: System.Security (in system.security.dll)

public class XmlDsigXPathTransform : Transform
public class XmlDsigXPathTransform extends Transform
public class XmlDsigXPathTransform extends Transform

The XmlDsigXPathTransform class allows you to address an XML document using the XPath language. This class uses an XPath expression to select the XML nodes you want to sign or encrypt while removing all others from either cryptographic operation.

Use the XmlDsigXPathTransform class to sign or encrypt specific parts of an XML document using an XPath expression. For information on initializing the XmlDsigXPathTransform class to the value of an XPath transform string, see the LoadInnerXml method.

The Uniform Resource Identifier (URI) that describes the XmlDsigXPathTransform class is defined by the XmlDsigXPathTransformUrl field.

For more information about the XPath transform, see Section 6.6.3 of the XMLDSIG specification, which is available from the W3C at www.w3.org/TR/xmldsig-core/.

This section contains two code examples. The first code example shows how to sign and verify an XML document using the XmlDsigXPathTransform class with an envelope signature. This example signs an XML document and saves the signature in a new XML document. The second code example demonstrates how to call members of the XmlDsigXPathTransform class.

Example #1

//
// 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();

        try
        {
            // Create an XML file to sign.
            CreateSomeXml("Example.xml");
            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.");
            }
            else
            {
                Console.WriteLine("The XML signature is not valid.");
            }
        }
        catch (CryptographicException e)
        {
            Console.WriteLine(e.Message);
        }
        finally
        {
            Key.Clear();
        }
    }

    // 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.
        reference.AddTransform(XPathTransform);

        // Add the reference to the SignedXml object.
        signedXml.AddReference(reference);

        // 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.
        signedXml.ComputeSignature();

        // 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));
        doc.WriteTo(xmltw);
        xmltw.Close();
    }
    // 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. 
        xmlDocument.Load(Name);

        // 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.
        signedXml.LoadXml((XmlElement)nodeList[0]);

        // 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. 
        xForm.LoadInnerXml(xPathElem.SelectNodes("."));

        // 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.
        document.AppendChild(node);

        // 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.
        document.DocumentElement.AppendChild(subnode);

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

Example #2

using System;
using System.IO;
using System.Xml;
using System.Security.Cryptography;
using System.Security.Cryptography.Xml;

class Class1
{
    [STAThread]
    static void Main(string[] args)
    {
        // Encrypt a sample XML string.
        XmlDocument productsXml = LoadProducts();
        ShowTransformProperties(productsXml);

        // Encrypt an XPath Xml string.
        XmlDocument transformXml = LoadTransformByXml();
        ShowTransformProperties(transformXml);

        // Use XmlDsigXPathTransform to resolve a Uri.
        Uri baseUri = new Uri("http://www.contoso.com");
        string relativeUri = "xml";
        Uri absoluteUri = ResolveUris(baseUri, relativeUri);

        Console.WriteLine("This sample completed successfully; " +
            "press Enter to exit.");
        Console.ReadLine();
    }

    // Encrypt the text in the specified XmlDocument.
    private static void ShowTransformProperties(XmlDocument xmlDoc)
    {

        // 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 = "ancestor-or-self::PRODUCTS";

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

        // Load the XPath XML from the element. 
        xmlTransform.LoadInnerXml(xPathElem.SelectNodes("."));

        // Ensure the transform is using the proper algorithm.
        xmlTransform.Algorithm =
            SignedXml.XmlDsigXPathTransformUrl;

        // Retrieve the XML representation of the current transform.
        XmlElement xmlInTransform = xmlTransform.GetXml();

        Console.WriteLine("\nXml representation of the current transform: ");
        Console.WriteLine(xmlInTransform.OuterXml);

        // Retrieve the valid input types for the current transform.
        Type[] validInTypes = xmlTransform.InputTypes;

        // Verify the xmlTransform can accept the XMLDocument as an
        // input type.
        for (int i = 0; i < validInTypes.Length; i++)
        {
            if (validInTypes[i] == xmlDoc.GetType())
            {
                // Load the document into the transfrom.
                xmlTransform.LoadInput(xmlDoc);

                try
                {
                    // This transform is created for demonstration purposes.
                    XmlDsigXPathTransform secondTransform =
                        new XmlDsigXPathTransform();

                    string classDescription = secondTransform.ToString();

                    xmlTransform.LoadInnerXml(xPathElem.SelectNodes(".")); ;
                }
                catch (CryptographicException)
                {
                    Console.WriteLine("Caught exception while trying to " +
                        "load the specified Xml document. The document " +
                        "requires an XPath element to be valid.");
                }
                break;
            }
        }

        Type[] validOutTypes = xmlTransform.OutputTypes;

        for (int i = validOutTypes.Length - 1; i >= 0; i--)
        {
            if (validOutTypes[i] == typeof(System.Xml.XmlDocument))
            {
                try
                {
                    Type xmlDocumentType = typeof(System.Xml.XmlDocument);
                    XmlDocument xmlDocumentOutput = (XmlDocument)
                        xmlTransform.GetOutput(xmlDocumentType);

                    // Display to the console the Xml before and after
                    // encryption.
                    Console.WriteLine("Result of the GetOutput method call" +
                        " from the current transform: " +
                        xmlDocumentOutput.OuterXml);
                }
                catch (Exception ex)
                {
                    Console.WriteLine("Unexpected exception caught: " +
                        ex.ToString());
                }

                break;
            }
            else if (validOutTypes[i] == typeof(System.Xml.XmlNodeList))
            {
                try
                {
                    Type xmlNodeListType = typeof(System.Xml.XmlNodeList);
                    XmlNodeList xmlNodes = (XmlNodeList)
                        xmlTransform.GetOutput(xmlNodeListType);

                    // Display to the console the Xml before and after
                    // encryption.
                    Console.WriteLine("Encoding the following message: " +
                        xmlDoc.InnerText);

                    Console.WriteLine("Nodes of the XmlNodeList retrieved " +
                        "from GetOutput:");
                    for (int j = 0; j < xmlNodes.Count; j++)
                    {
                        Console.WriteLine("Node " + j +
                            " has the following name: " +
                            xmlNodes.Item(j).Name +
                            " and the following InnerXml: " +
                            xmlNodes.Item(j).InnerXml);
                    }
                }
                catch (Exception ex)
                {
                    Console.WriteLine("Unexpected exception caught: " +
                        ex.ToString());
                }

                break;
            }
            else
            {
                object outputObject = xmlTransform.GetOutput();
            }
        }
    }

    // Create an XML document for the dsig namespace.
    private static XmlDocument LoadTransformByXml()
    {
        XmlDocument xmlDoc = new XmlDocument();

        string transformXml = "<Signature><Reference URI=''><Transforms>";
        transformXml += "<Transform><XPath ";
        transformXml += "xmlns:dsig='http://www.w3.org/2000/09/xmldsig#'>";
        transformXml += "not(ancestor-or-self::dsig:Signature)";
        transformXml += "</XPath></Transform>";
        transformXml += "</Transforms></Reference></Signature>";

        xmlDoc.LoadXml(transformXml);
        return xmlDoc;
    }

    // Create an XML document describing various products.
    private static XmlDocument LoadProducts()
    {
        XmlDocument xmlDoc = new XmlDocument();

        string contosoProducts = "<PRODUCTS>";
        contosoProducts += "<PRODUCT><ID>123</ID>";
        contosoProducts += "<DESCRIPTION>Router</DESCRIPTION></PRODUCT>";
        contosoProducts += "<PRODUCT><ID>456</ID>";
        contosoProducts += "<DESCRIPTION>Keyboard</DESCRIPTION></PRODUCT>";
        contosoProducts += "<PRODUCT><ID>789</ID>";
        contosoProducts += "<DESCRIPTION>Monitor</DESCRIPTION></PRODUCT>";
        contosoProducts += "</PRODUCTS>";

        xmlDoc.LoadXml(contosoProducts);
        return xmlDoc;
    }

    // Resolve the specified base and relative Uri's .
    private static Uri ResolveUris(Uri baseUri, string relativeUri)
    {
        XmlUrlResolver xmlResolver = new XmlUrlResolver();
        xmlResolver.Credentials =
            System.Net.CredentialCache.DefaultCredentials;

        XmlDsigXPathTransform xmlTransform =
            new XmlDsigXPathTransform();
        xmlTransform.Resolver = xmlResolver;

        Uri absoluteUri = xmlResolver.ResolveUri(baseUri, relativeUri);

        if (absoluteUri != null)
        {
            Console.WriteLine(
                "\nResolved the base Uri and relative Uri to the following:");
            Console.WriteLine(absoluteUri.ToString());
        }
        else
        {
            Console.WriteLine(
                "Unable to resolve the base Uri and relative Uri");
        }
        return absoluteUri;
    }
}

System.Object
   System.Security.Cryptography.Xml.Transform
    System.Security.Cryptography.Xml.XmlDsigXPathTransform
Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 98, Windows 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 .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0, 1.1, 1.0
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