SignedXml.CheckSignature方法（X509Certificate2，false）不检查证书有效性

Question

I am trying to validate the signature as well as the certificate by passing false in the method as the second parameter - SignedXml.CheckSignature(Cert,false) However, even If the certificate used (created by makecert as given in the example below) is not expired, the CheckSignature() always returns false.

If you pass false (validate signature only) as the second parameter, It returns true though. So, now the question is - the verifySignatureOnly parameter - If assigned false - what does It actually check in the certificate? Does It consider the expire date of the certificate as a criteria to ascertain the validity of the certificate?

Below code was taken from MSDN page

// 
// 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 01/01/2015 -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.");
            }
            Console.ReadLine();
        }
        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, false);

    }


    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.

Answer 1

When verifying the cert, it's not only the validity time that is checked but also the key usage flags and the chain of trust.

Make sure your cert is approved for signing and add it as a trusted certificate to your certificate store. That should make it work.