Mono c# Websocket library throws errors on incoming wss-connection requests under linux

Question

I developed a websocket-server in C# with Mono under linux and the Websocket library called Fleck Websockets

Javascript clients in Browsers are connecting and running smoothly with the websocket protocoll ws.

Now I want to use wss as the secure websocket connection.

The library claims to be able to handle this by just pointing to the .pfx X509 certificate.

I also incorporated the solution from Mono Documentation which might be outdated though.

WebSocketServer server = new WebSocketServer("wss://" + Tools.LocalIPAddress()  + ":" + MainClass.websocketport);
server.Certificate = new 

// Mono Hack for Handling potential Certificate problems
ServicePointManager.ServerCertificateValidationCallback = Validator;

System.Security.Cryptography.X509Certificates.X509Certificate2(new System.Security.Cryptography.X509Certificates.X509Certificate(zertifikatsfile,"<password>"));
server.EnabledSslProtocols = System.Security.Authentication.SslProtocols.Tls;

public static bool Validator(System.Object sender,
            X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors)
        {
            return true;
         }

However, once a wss-client (Browser) tries to connect, the programm throws the folling error/warning

[Warn] Failed to Authenticate System.AggregateException: One or more errors occured ---> System.IO.IOException: The authentication or decryption has failed. ---> System.NotSupportedException: Unsupported security protocol type
  at Mono.Security.Protocol.Tls.Context.DecodeProtocolCode (Int16 code) [0x00000] in <filename unknown>:0 
  at Mono.Security.Protocol.Tls.Handshake.Server.TlsClientHello.processProtocol (Int16 protocol) [0x00000] in <filename unknown>:0 
  at Mono.Security.Protocol.Tls.Handshake.Server.TlsClientHello.ProcessAsTls1 () [0x00000] in <filename unknown>:0 
  at Mono.Security.Protocol.Tls.Handshake.HandshakeMessage.Process () [0x00000] in <filename unknown>:0 
  at (wrapper remoting-invoke-with-check) Mono.Security.Protocol.Tls.Handshake.HandshakeMessage:Process ()
  at Mono.Security.Protocol.Tls.ServerRecordProtocol.ProcessHandshakeMessage (Mono.Security.Protocol.Tls.TlsStream handMsg) [0x00000] in <filename unknown>:0 
  at Mono.Security.Protocol.Tls.RecordProtocol.InternalReceiveRecordCallback (IAsyncResult asyncResult) [0x00000] in <filename unknown>:0 
  --- End of inner exception stack trace ---
  at Mono.Security.Protocol.Tls.SslStreamBase.AsyncHandshakeCallback (IAsyncResult asyncResult) [0x00000] in <filename unknown>:0 
  --- End of inner exception stack trace ---
 --> (Inner exception 0) System.IO.IOException: The authentication or decryption has failed. ---> System.NotSupportedException: Unsupported security protocol type
  at Mono.Security.Protocol.Tls.Context.DecodeProtocolCode (Int16 code) [0x00000] in <filename unknown>:0 
  at Mono.Security.Protocol.Tls.Handshake.Server.TlsClientHello.processProtocol (Int16 protocol) [0x00000] in <filename unknown>:0 
  at Mono.Security.Protocol.Tls.Handshake.Server.TlsClientHello.ProcessAsTls1 () [0x00000] in <filename unknown>:0 
  at Mono.Security.Protocol.Tls.Handshake.HandshakeMessage.Process () [0x00000] in <filename unknown>:0 
  at (wrapper remoting-invoke-with-check) Mono.Security.Protocol.Tls.Handshake.HandshakeMessage:Process ()
  at Mono.Security.Protocol.Tls.ServerRecordProtocol.ProcessHandshakeMessage (Mono.Security.Protocol.Tls.TlsStream handMsg) [0x00000] in <filename unknown>:0 
  at Mono.Security.Protocol.Tls.RecordProtocol.InternalReceiveRecordCallback (IAsyncResult asyncResult) [0x00000] in <filename unknown>:0 
  --- End of inner exception stack trace ---
  at Mono.Security.Protocol.Tls.SslStreamBase.AsyncHandshakeCallback (IAsyncResult asyncResult) [0x00000] in <filename unknown>:0 

I am now not sure how to proceed to overcome the problem. As a further background information, the Certificate is from letsencrypt and I converted it with openssl to .pfx.

Answer 1

System.IO.IOException: The authentication or decryption has failed. ---> System.NotSupportedException: Unsupported security protocol type

This error above hints me that you're using a version of Debian (8.10) which includes a version of Mono (4.6.2) which is a bit old. Mono 4.8.x and newer includes better TLS/cryptography support, upgrade to this version and test again.