SignedXml.CheckSignature Method (X509Certificate2, Boolean)

Determines whether the Signature property verifies for the specified X509Certificate2 object and, optionally, whether the certificate is valid.

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

[ComVisibleAttribute(false)]
public bool CheckSignature(
	X509Certificate2 certificate,
	bool verifySignatureOnly
)

Parameters

certificate
Type: System.Security.Cryptography.X509Certificates.X509Certificate2

The X509Certificate2 object to use to verify the Signature property.

verifySignatureOnly
Type: System.Boolean

true to verify the signature only; false to verify both the signature and certificate.

Return Value

Type: System.Boolean
true if the signature is valid; otherwise, false.
-or-
true if the signature and certificate are valid; otherwise, false.

ExceptionCondition
ArgumentNullException

The certificate parameter is null.

CryptographicException

A signature description could not be created for the certificate parameter.

In version 1.1 of the .NET Framework, the X.509 certificate is not verified. In version 2.0 and later, the X.509 certificate is verified.

In version 2.0 and later of the .NET Framework, the CheckSignature method will search the "AddressBook" store for certificates suitable for the verification. For example, if the certificate is referenced by a Subject Key Identifier (SKI), the CheckSignature method will select certificates with this SKI and try them one after another until it can verify the certificate.

The following code example uses an X.509 certificate from a certificate store to sign and verify an XML document.

// 
// This example signs an XML file using an 
// envelope signature. It then verifies the  
// signed XML. 
// 
// You must have a certificate with a subject name 
// of "CN=XMLDSIG_Test" in the "My" certificate store. 
// 
// Run the following command to create a certificate 
// and place it in the store. 
// makecert -r -pe -n "CN=XMLDSIG_Test" -b 01/01/2005 -e 01/01/2010 -sky signing -ss my

using System;
using System.Security.Cryptography;
using System.Security.Cryptography.Xml;
using System.Security.Cryptography.X509Certificates;
using System.Text;
using System.Xml;

public class SignVerifyEnvelope
{

    public static void Main(String[] args)
    {

        string Certificate = "CN=XMLDSIG_Test";

        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", Certificate);
            Console.WriteLine("XML file signed.");

            if (VerifyXmlFile("SignedExample.xml", Certificate))
            {
                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, string SubjectName)
    {
        if (null == FileName)
            throw new ArgumentNullException("FileName");
        if (null == SignedFileName)
            throw new ArgumentNullException("SignedFileName");
        if (null == SubjectName)
            throw new ArgumentNullException("SubjectName");

        // Load the certificate from the certificate store.
        X509Certificate2 cert = GetCertificateBySubject(SubjectName);

        // 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 = cert.PrivateKey;

        // 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);

        // Create a new KeyInfo object.
        KeyInfo 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.
        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. 
        using (XmlTextWriter xmltw = new XmlTextWriter(SignedFileName, new UTF8Encoding(false)))
        {
            doc.WriteTo(xmltw);
            xmltw.Close();
        }

    }

    // Verify the signature of an XML file against an asymetric  
    // algorithm and return the result. 
    public static Boolean VerifyXmlFile(String FileName, String CertificateSubject)
    {
        // Check the args. 
        if (null == FileName)
            throw new ArgumentNullException("FileName");
        if (null == CertificateSubject)
            throw new ArgumentNullException("CertificateSubject");

        // Load the certificate from the store.
        X509Certificate2 cert = GetCertificateBySubject(CertificateSubject);

        // Create a new XML document.
        XmlDocument xmlDocument = new XmlDocument();

        // Load the passed XML file into the document. 
        xmlDocument.Load(FileName);

        // 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(cert, true);

    }


    public static X509Certificate2 GetCertificateBySubject(string CertificateSubject)
    {
        // Check the args. 
        if (null == CertificateSubject)
            throw new ArgumentNullException("CertificateSubject");


        // Load the certificate from the certificate store.
        X509Certificate2 cert = null;

        X509Store store = new X509Store("My", StoreLocation.CurrentUser);

        try
        {
            // Open the store.
            store.Open(OpenFlags.ReadOnly | OpenFlags.OpenExistingOnly);

            // Get the certs from the store.
            X509Certificate2Collection CertCol = store.Certificates;

            // Find the certificate with the specified subject. 
            foreach (X509Certificate2 c in CertCol)
            {
                if (c.Subject == CertificateSubject)
                {
                    cert = c;
                    break;
                }
            }

            // Throw an exception of the certificate was not found. 
            if (cert == null)
            {
                throw new CryptographicException("The certificate could not be found.");
            }
        }
        finally
        {
            // Close the store even if an exception was thrown.
            store.Close();
        }

        return cert;
    }

    // Create example data to sign. 
    public static void CreateSomeXml(string FileName)
    {
        // Check the args. 
        if (null == FileName)
            throw new ArgumentNullException("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 file name specified. 
        using (XmlTextWriter xmltw = new XmlTextWriter(FileName, new UTF8Encoding(false)))
        {
            document.WriteTo(xmltw);

            xmltw.Close();
        }
    }
}
// This code example displays the following to the console: 
// 
// New XML file created. 
// XML file signed. 
// The XML signature is valid.

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

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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