.Net Programming: What to validate on an SSL self-signed certificate

.net, ssl-certificate

Solution

If you're using self signed certs then the only errors you should expect is a chain error on the root (Cert. Issuer). I would suggest something like this that traps for that chain error specifically and lets all other errors fall through.

ServicePointManager.ServerCertificateValidationCallback += new RemoteCertificateValidationCallback(
    ValidateRemoteCertificate
);

private static bool ValidateRemoteCertificate(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors policyErrors )
{
    string trustedIssuer = "CN=www.domain.com";
    string trustedDomain = "CN=www.domain.com";
    bool policyErr = false;

    switch (policyErrors)
    {
        case SslPolicyErrors.None:
            policyErr |= false;
            break;
        case SslPolicyErrors.RemoteCertificateChainErrors:
            bool chainErr = false;
            foreach (X509ChainStatus status in chain.ChainStatus)
            {
                switch (status.Status)
                {
                    case X509ChainStatusFlags.NoError:
                        chainErr |= false;
                        break;
                    case X509ChainStatusFlags.UntrustedRoot:
                        if (certificate.Subject != trustedDomain || certificate.Issuer != trustedIssuer)
                            chainErr |= true;
                        else
                            chainErr |= false;
                        break;
                    default:
                        chainErr |= true;
                        break;
                }                    
            }
            policyErr |= chainErr;
            break;
        default:
            policyErr |= true;
            break;
    }

    return !policyErr;
}

Problem

I cannot get the users to create real certs for their servers but I'd like to do some security checks. So the following is too light because, as I read it, there is no checking on the certs. ``` ServicePointManager.ServerCertificateValidationCallback = delegate { return true; }; ``` What do you recommend that I have the clients check on the x509 cert? Given that I'm using a .NET language (c#/f#).

Original source