Bosch Smart Home API C# RestRequest Error "The request was aborted: Could not create SSL/TLS secure channel."

Question

I'm trying to use RestSharp to call the local Bosch Smart Home API. The Documentation by Bosch shows how to use Postman to HTTP-Request the local API, which all functions properly. I can even request a Device-List, after creating a self-signed Certificate and setting Postman up accordingly. So I tried to develop a simple C# Code to request the same list via RestSharp.

static void RestGet()
        {
            System.Net.ServicePointManager.ServerCertificateValidationCallback = delegate { return true; };
            const String WEBSERVICE_URL = "https://10.20.1.41:8444/smarthome/devices";
            const string certificate_path = @"C:\Users\niko\Documents\certificates\certificate.pfx";
            const string certificate_pass = "....";
            const string systemPassword = "...."; //encrypted in BASE64
            string ua = "User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:8.0) Gecko/20100101 Firefox/8.0";

            ServicePointManager.Expect100Continue = true;
            ServicePointManager.DefaultConnectionLimit = 9999;
            ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12 | SecurityProtocolType.Ssl3;


            var client = new RestClient("https://10.20.1.41:8444/smarthome/devices");
            client.Timeout = 100000;
            X509Certificate2 cer = new X509Certificate2(certificate_path, certificate_pass);
            client.ClientCertificates = new X509CertificateCollection() { cer };
            var request = new RestRequest(Method.GET);
            request.AddHeader("Content-Type", "application/json");
            request.AddHeader("api-version", "1.0");
            request.AddHeader("Systempassword", systemPassword);
            IRestResponse response = client.Execute(request);
            Console.WriteLine(response.ErrorMessage);
            Console.WriteLine(response.Content);
            Console.ReadKey();
        }

For some reason the Server just sends the ErrorMessage:

The request was aborted: Could not create SSL/TLS secure channel.

I've been trying to figure it out for the whole day, but since the API is pretty new, there isn't any info up about it yet.

Answer 1

So. Once I noticed that the request would actually succeed while Fiddler was open in the Background, I knew my error had to be how I load the certificate into my program (Because Fiddler uses a seperate certificate, that you have to provide). The first thing I did after noticing that, was copying the certificate I provided Fiddler into my project and loading that into the program. AND IT FINALLY WORKS! I can't tell you how that certificate was different from the other ones.