C# is not trusting installed certificate

Question

I set up a FTP server in IIS with an SSL certificate which I created my self (using Makecert.exe and Pvk2Pfx). I attributed the PFX file to my FTP server.

I have a C# script which connects to the FTP server and always gets the following error message:

System.Security.Authentication.AuthenticationException: The remote certificate is invalid according to the validation procedure.

I installed the certificate in the "Trusted Root Certification Authorities" in the local computer and user.

As it does not authenticate, I took a look via C# on the store:

X509Store store = new X509Store(StoreName.AuthRoot, StoreLocation.LocalMachine);
store.Open(OpenFlags.ReadOnly | OpenFlags.OpenExistingOnly);

foreach (X509Certificate2 mCert in store.Certificates)
{
     var friendlyName = mCert.Issuer;
     Console.WriteLine(friendlyName);
}
store.Close();

But my certificate is not listed. When I open the MMC console I see my certificate.

Answer 1

Usually, C# doesn't trust certificates without a trusted root certificate - like in the case of a self-signed certificate. The ServicePointManagerallows to add a function where you can handle trusts yourself.

// Callback used to validate the certificate in an SSL conversation
private static bool ValidateRemoteCertificate(
    object sender,
    X509Certificate certificate,
    X509Chain chain,
    SslPolicyErrors policyErrors)
{
    if (Convert.ToBoolean(ConfigurationManager.AppSettings["IgnoreSslErrors"]))
    {
        // Allow any old dodgy certificate...
        return true;
    }
    else
    {
        return policyErrors == SslPolicyErrors.None;
    }
}

private static string MakeRequest(string uri, string method, WebProxy proxy)
{
    HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create(uri);
    webRequest.AllowAutoRedirect = true;
    webRequest.Method = method;

    // Allows for validation of SSL conversations
ServicePointManager.ServerCertificateValidationCallback += new RemoteCertificateValidationCallback(
    ValidateRemoteCertificate);

    if (proxy != null)
    {
        webRequest.Proxy = proxy;
    }

    HttpWebResponse response = null;
    try
    {
        response = (HttpWebResponse)webRequest.GetResponse();
        using (Stream s = response.GetResponseStream())
        {
            using (StreamReader sr = new StreamReader(s))
            {
                return sr.ReadToEnd();
            }
        }
    }
    finally
    {
        if (response != null)
            response.Close();
    }
}

From blog post How to accept an invalid SSL certificate programmatically.