How do I manually validate a self-signed certificate in C#?

Question

I’ve been working a lot in Docker containers in the past couple of weeks and I came across the obstacle where a self signed cert was causing issues because the Docker container did not recognize the Certificate Authority.

The issue was that I was unable to put my own certs on the server configuration because the way we use Docker at my company.

Answer 1

After a good bit of research, I came up with a solution that manually validates the cert based off building the chain and verification of the thumbprint.

Note: You have to be using a library that supports a Certificate Validation Callback so that you can code your own delegate method. Below is my implementation.

public static bool ManualSslVerification(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors)
{
    try
    {
        //Testing to see if the Certificate and Chain build properly, aka no forgery.
        chain.ChainPolicy.VerificationFlags = X509VerificationFlags.NoFlag;
        chain.ChainPolicy.RevocationMode = X509RevocationMode.NoCheck;
        chain.Build(new X509Certificate2(certificate));

        //Looking to see if there are no errors in the build that we don’t like
        foreach (X509ChainStatus status in chain.ChainStatus)
        {
            if (status.Status == X509ChainStatusFlags.NoError || status.Status == X509ChainStatusFlags.UntrustedRoot)
            {
                //Acceptable Status, We want to know if it builds properly.
            }
            else
            {
                return false;
            }
        }

        X509Certificate2 trustedRootCertificateAuthority = new X509Certificate2(ViewController.Properties.Resources.My_Infrastructure_Root_CA);

        //Now that we have tested to see if the cert builds properly, we now will check if the thumbprint of the root ca matches our trusted one
        if(chain.ChainElements[chain.ChainElements.Count – 1].Certificate.Thumbprint != trustedRootCertificateAuthority.Thumbprint)
        {
            return false;
        }

        //Once we have verified the thumbprint the last fun check we can do is to build the chain and then see if the remote cert builds properly with it
        //Testing to see if the Certificate and Chain build properly, aka no forgery.
        X509Chain trustedChain = new X509Chain();
        trustedChain.ChainPolicy.ExtraStore.Add(trustedRootCertificateAuthority);
        trustedChain.ChainPolicy.VerificationFlags = X509VerificationFlags.NoFlag;
        trustedChain.ChainPolicy.RevocationMode = X509RevocationMode.NoCheck;
        trustedChain.Build(new X509Certificate2(certificate));

        //Looking to see if there are no errors in the build that we don’t like
        foreach (X509ChainStatus status in trustedChain.ChainStatus)
        {
            if(status.Status == X509ChainStatusFlags.NoError || status.Status == X509ChainStatusFlags.UntrustedRoot)
            {
                //Acceptable Status, We want to know if it builds properly.
            }
            else
            {
                return false;
            }
        }
    }
    catch (Exception ex)
    {
        Console.WriteLine(ex);
        return false;
    }

    return true;
}