Versions Compared

Key

  • This line was added.
  • This line was removed.
  • Formatting was changed.

...

  1. TLS with Server Certificate Authentication

  2. TLS with Server and Client Certificate Authentication

Steps for Creating Certificates for

...

For this step, the server (the broker) authenticates to the client with a certificate before the TLS connection is established. The client does not authenticate to the broker with a certificate, but may do so through other means (password, etc.).

The outputs for this process are:

  • ca.key file - to be kept private to (this) system that generated it.

  • ca.pem file - public certificate authority (self signed) certificate, to be distributed.

  • server.key file - to be kept private to where the MQTT broker (the TLS server) resides.

  • server.pem file - public server certificate, to be distributed to the MQTT broker.

One or more server certificates can be created, one for each MQTT broker. The server certificate contains the IP or hostname of that server. During TLS session establishment, the TLS client (eACM-MQTT, Bridge, Edge Manager, etc.) will compare the IP or hostname that it is connecting to with the CN (Common Name) presented by the server certificate. If there is a match, the TLS client will attempt to connect to the server. If not, the TLS client will drop the connection and regard it as unverified and untrusted. You may choose to break this rule by unchecking the “Verify Certificate” box (not recommended).

Info

Leaving the “Verify Certificate” box unchecked may expose your TLS client to Man-in-the-Middle attacks. You have an encrypted connection, but have not proven to whom you are connected.

The inputs for this process are:

  • Hostname or IP of your MQTT broker’s server, to be used in the CN of the server certificate

  • Password for ca.key (optional)

  • Password for server.key (optional)

The exact steps in this process can be varied according to your needs. What follows is an example.

Create the key pair (ca.key) used by your certificate authority. To protect it with a password (you will be prompted):

Code Block
openssl genrsa -aes256 -out ca.key 2048

To create ca.key without a password:

Code Block
openssl genrsa -out ca.key 2048

Create the self signed certificate authority certificate (ca.pem). If you used a password when creating ca.key, you will be prompted for it.

Code Block
openssl req -new -x509 -days 3650 -extensions v3_ca -key ca.key -out ca.pem -subj "/C=US/ST=Texas/O=THIS_COMPANY INC/CN=John Smith/emailAddress=johnsmith@gmail.com" --outform PEM

Create the key pair (server.key) used by your broker.

It is important to note that this step can (and probably should) take place where broker is installed and kept private there.

To protect it with a password (you will be prompted):

Code Block
openssl genrsa -aes256 -out server.key 2048

To create server.key without a password:

Code Block
openssl genrsa -out server.key 2048

Create the certificate signing request for the server (the broker), server.csr. If you created ca.key on a different machine, you will need to copy server.csr to that machine.

If you protected server.key with a password, you will be prompted.

In this example, you will need to substitute 10.3.0.11 with the IP or hostname of your broker’s server for TLS verification to work correctly.

Code Block
openssl req -out server.csr -key server.key -new -subj "/C=US/ST=Texas/O=THIS_COMPANY INC/CN=10.3.0.11/emailAddress=johnsmith@gmail.com" --outform PEM
Info

The server certificate’s CN field should match the hostname or IP of the MQTT broker.

Create the server certificate (server.pem). The step must take place where you have your ca.key. The server.csr and ca.pem files are also required. If you used a password when creating your ca.key, you will be prompted for it.

Code Block
openssl x509 -req -in server.csr -CA ca.pem -CAkey ca.key -CAcreateserial -out server.pem -days 3650 --outform PEM

Configuration

You now have all the files required to configure your client and server (broker) for TLS authentication.

  1. You will need to provide ca.pem to both your client and server.

  2. You will need to provide server.key and server.pem to your server.

Client

In older versions of eACM, you must copy (scp) your ca.pem to the host where eACM is installed and reference the path to it in your TLS Settings object (MQTT app) or the Broker 1/2 tab of your Node object (Edge Manager). Assign ca.pem to the CA File property of the object.

In newer versions of eACM, you can upload your ca.pem using the TLS Settings object form or Node object form. Assign ca.pem to the CA File property of the object.

Server (Broker)

The broker configuration will be different for each broker. Example for mosquitto:

Code Block
per_listener_settings true

listener 8883
allow_anonymous false
require_certificate false
certfile C:\Users\myuser\Documents\certs\server.pem
keyfile C:\Users\myuser\Documents\certs\server.key
cafile C:\Users\myuser\Documents\certs\ca.pem
password_file C:\Users\myuser\Documents\mosquitto\user-passwd.txt

...

Client Authentication

For this step, the client (the eACM MQTT app, Bridge, Edge Manager, etc.) authenticates to the server with a certificate before the TLS connection is fully established. This takes place after the server has authenticated to to the client with its own (server) certificate.

Info

All of the steps above under “Steps for Creating Certificates for Server Authentication” must be completed first before proceeding.

...

Code Block
openssl x509 -req -in client.csr -CA ca.pem -CAkey ca.key -CAcreateserial -out client.pem -days 3650 --outform PEM

Configuration

You now have all the files required to configure your client and server (broker) for TLS authentication with both server authentication and client authentication.

  1. You will need to provide ca.pem to both your client and server.

  2. You will need to provide server.key and server.pem to your server.

  3. You will need to provide client.key and client.pem to each client. The client will also need to be provided with the password used to encrypt its client.key.

Client

In older versions of eACM, you must copy (scp) your ca.pem, client.key and client.pem to the host where eACM is installed and reference the path to it in your TLS Settings object (MQTT app) or the Broker 1/2 tab of your Node object (Edge Manager).

...

Assign the password used to encrypt client.key to Private Key Password.

Server (Broker)

The broker configuration will be different for each broker. Example for mosquitto:

...

Code Block
user MyEACM
topic read STATE/+
topic readwrite spBv1.0/#

user SparkplugViewer
topic read STATE/+
topic read spBv1.0/#

user HMI
topic readwrite STATE/+
topic readwrite spBv1.0/#

What to do when authentication fails

When the MQTT client (eACM, Edge Manager or Bridge) fail to connect to the broker the first thing to do is to enable logging on your MQTT broker. Then compare the broker logging in the context of logging from eACM.

...