Documentation > Administration > Going to Production > Secure WebSocket and HTTPS

Secure WebSocket and HTTPS

For production use, it is strongly recommended to always run WebSocket over TLS ("secure WebSocket"). This is mainly for two reasons:

  • keeping your and your user's data confidential and untampered
  • avoiding issues with WebSocket on networks that employ so-called intermediaries (proxies, caches, firewalls)

The latter is especially important in locked down enterprise environments and on mobile operator networks. By using secure WebSocket ("wss"), WebSocket will work in almost all circumstances (exceptions potentially being TLS interception / MITM proxies).

Crossbar.io has full support for running secure WebSocket and HTTPS. We discuss configuration:

To actually use TLS, you will need a certificate for your server. This guide describes the three main options:

  1. Using self-signed certificates
  2. Using certificates from commercial CAs
  3. Creating and using your own CA

We also strongly recommend to test your server using the SSL Server Test provided by Qualys SSL Labs. This will point out weaknesses in your configuration or issues with your certificate.

WebSocket Transport Configuration

To configure a WebSocket transport for TLS, include a tls dictionary with (mandatory) attributes key and certificate in your transport configuration. Here is an example:

{
   "type": "websocket",
   "endpoint": {
      "type": "tcp",
      "port": 443,
      "tls": {
         "key": "server_key.pem",
         "certificate": "server_cert.pem"
      }
   },
   "url": "wss://example.com"
}

The key must point to the server's private key file (PEM format, no passphrase), and the certificate must point to the server's certificate file (PEM format). The paths can be relative to the node directory, or absolute.

To configure a Web transport for TLS, here is an example:

{
   "type": "web",
   "endpoint": {
      "type": "tcp",
      "port": 443,
      "tls": {
         "key": "server_key.pem",
         "certificate": "server_cert.pem"
      }
   },
   "paths": {
      "/": {
         "type": "static",
         "directory": ".."
      },
      "ws": {
         "type": "websocket",
         "url": "wss://example.com/ws"
      }
   }
}
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Endpoint TLS Configuration

The TLS configuration has a couple of options:

{
   "type": "websocket",
   "endpoint": {
      "type": "tcp",
      "port": 443,
      "tls": {
         "key": "server_key.pem",
         "certificate": "server_cert.pem",
         "ca_certificates": [
            "ca.cert.pem",
            "intermediate.cert.pem"
        ],
         "dhparam": "dhparam.pem",
         "ciphers": "ECDH+AESGCM:DH+AESGCM:ECDH+AES256:DH+AES256:ECDH+AES128:DH+AES:ECDH+3DES:DH+3DES:RSA+AES:RSA+3DES:!ADH:!AECDH:!MD5:!DSS"
      }
   },
   "url": "wss://example.com"
}

where

  • key is the filesystem path to the server private key file (PEM format, no passphrase) (mandatory)
  • certificate is the filesystem path to the server certificate file (PEM format) (mandatory)
  • ca_certificates when set requires that a connecting client's certificate be issued by one of the listed CAs, otherwise the connection establishment will be denied (optional)
  • dhparam is the filesystem path to a Diffie-Hellman parameter file - see explanation below (optional)
  • ciphers is a list of ciphers the server is willing to use with a client - see explanation below (optional)

Diffie-Hellman

To use Diffie-Hellman based key exchange, you need to generate a parameter file:

openssl dhparam -2 4096 -out .crossbar/dhparam.pem

The use of Diffie-Hellman key exchange is desirable, since this provides Perfect Forward Secrecy (PFS). Without a DH parameter file, no Diffie-Hellman based ciphers will be used, even if configured to do so.

Elliptic Curve Ciphers

Using elliptic curve based ciphers ("ECDH/ECDHE") is generally considered desirable, since shorter keys than RSA support strong encryption already consuming less CPU cycles.

Prerequisites for EC Support

EC crypto is fully supported by Crossbar.io, if the underlying OpenSSL library supports EC and you have pyOpenSSL >= 0.15 running.

You can check like this:

openssl ecparam -list_curves

To install pyOpenSSL trunk (since 0.15 isn't released yet - 2014/07/09):

cd ~
git clone git@github.com:pyca/pyopenssl.git
cd pyopenssl
python setup.py install

Crossbar.io uses the prime256v1 curve by default.

prime256v1(X9.62/SECG) is an elliptic curve over a 256 bit prime field. This is elliptic curve "NIST P-256" from here.

This seems to be the most widely used curve and researchers think it is "ok" (other than wrt timing attacks etc that might lurk inside OpenSSL itself).

Ciphers

Crossbar.io will by default run a very strong and conservative set of ciphers:

ECDHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA256:ECDHE-RSA-AES128-SHA:DHE-RSA-AES128-SHA

Above configuration activates exactly 6 ciphers to be used, all of which provide Forward Secrecy.

Note that the default configuration does not support Windows XP!. If you must support XP, you will need to modify the ciphers configuration.

In general, you should only change the ciphers if you know what you are doing.

The ciphers parameter must be in the format as used by OpenSSL, and the OpenSSL library version installed on the system must support the ciphers configured to make same actually available. If your OpenSSL version installed does not support a configured cipher (e.g. ECDH elliptic curve based), the ciphers not available will simply be skipped.

TLS Certificates

We provide help for creation and handling of TLS certificates on the TLS Certificates page.

Examples

Resources