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SignedXml.CheckSignature Method (KeyedHashAlgorithm)

Determines whether the Signature property verifies for the specified message authentication code (MAC) algorithm.

Namespace:  System.Security.Cryptography.Xml
Assembly:  System.Security (in System.Security.dll)
public bool CheckSignature(
	KeyedHashAlgorithm macAlg
)

Parameters

macAlg
Type: System.Security.Cryptography.KeyedHashAlgorithm

The implementation of KeyedHashAlgorithm that holds the MAC to be used to verify the Signature property.

Return Value

Type: System.Boolean
true if the Signature property verifies for the specified MAC; otherwise, false.
ExceptionCondition
ArgumentNullException

The macAlg parameter is null.

CryptographicException

The HashSize property of the specified KeyedHashAlgorithm object is not valid.

-or-

The Signature property is null.

-or-

The cryptographic transform used to check the signature could not be created.

The following code example shows how to sign and verify a Uniform Resource Identifier (URI) addressable object using a detached signature.

// 
// This example signs a file specified by a URI  
// using a detached signature. It then verifies   
// the signed XML. 
// 

using System;
using System.Security.Cryptography;
using System.Security.Cryptography.Xml;
using System.Text;
using System.Xml;



class XMLDSIGDetached
{
	
    [STAThread]
    static void Main(string[] args)
    {
        try
        {
            // The URI to sign. 
            string resourceToSign = "http://www.microsoft.com";
		
            // The name of the file to which to save the XML signature. 
            string XmlFileName = "xmlsig.xml";

            // Generate a signing key.
            HMACSHA1 Key = new HMACSHA1();

            Console.WriteLine("Signing: {0}", resourceToSign);

            // Sign the detached resourceand save the signature in an XML file.
            SignDetachedResource(resourceToSign, XmlFileName, Key);

            Console.WriteLine("XML signature was succesfully computed and saved to {0}.", XmlFileName);

            // Verify the signature of the signed XML.
            Console.WriteLine("Verifying signature...");

            //Verify the XML signature in the XML file. 
            bool result = VerifyDetachedSignature(XmlFileName, Key);

            // 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);
        }
		
			
    }

    // Sign an XML file and save the signature in a new file. 
    public static void SignDetachedResource(string URIString, string XmlSigFileName, KeyedHashAlgorithm Key)
    {
        // Create a SignedXml object.
        SignedXml signedXml = new SignedXml();

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

        // Add the passed URI to the reference object.
        reference.Uri = URIString;
		
        // Add the reference to the SignedXml object.
        signedXml.AddReference(reference);

        // Compute the signature.
        signedXml.ComputeSignature(Key);

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

        // Save the signed XML document to a file specified 
        // using the passed string.
        XmlTextWriter xmltw = new XmlTextWriter(XmlSigFileName, new UTF8Encoding(false));
        xmlDigitalSignature.WriteTo(xmltw);
        xmltw.Close();

    }

    // Verify the signature of an XML file and return the result. 
    public static Boolean VerifyDetachedSignature(string XmlSigFileName, KeyedHashAlgorithm Key)
    {	
        // Create a new XML document.
        XmlDocument xmlDocument = new XmlDocument();

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

        // 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(Key);
    }

}

The following code example shows how to sign and verify an entire XML document using an enveloping 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)
    {
        try
        {

            // Generate a signing key.
            HMACSHA1 Key = new HMACSHA1();

            // 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);
            Console.WriteLine("XML file signed."); 

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

            // 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);
        }
    }


    // Sign an XML file and save the signature in a new file. 
    public static void SignXmlFile(string FileName, string SignedFileName, KeyedHashAlgorithm Key)
    {
        // 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);

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

        // Add an enveloped transformation to the reference.
        XmlDsigEnvelopedSignatureTransform env = new XmlDsigEnvelopedSignatureTransform();
        reference.AddTransform(env);

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

        // Compute the signature.
        signedXml.ComputeSignature(Key);

        // 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));
		
		
        if (doc.FirstChild is XmlDeclaration)  
        {
            doc.RemoveChild(doc.FirstChild);
        }

        // 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, KeyedHashAlgorithm Key)
    {
        // Create a new XML document.
        XmlDocument xmlDocument = new XmlDocument();

        // Format using whitespaces.
        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(Key);
    }


    // 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, "", "MyElement", "samples");
		
        // Add some text to the node.
        node.InnerText = "Example text to be signed.";

        // Append the node to the document.
        document.AppendChild(node);

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

}

.NET Framework

Supported in: 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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