Enable two-way SSL/TLS for EMQ X

As a security protocol based on modern cryptographic public key algorithms, TLS/SSL can ensure the security of transmission in the computer communication network. EMQ X has built-in support for TLS/SSL including one-way/two-ways authentication, the X.509 certificate, load balance SSL and many other security certifications. You can enable SSL/TLS for all protocols supported by EMQ X, and can also configure HTTP API provided by EMQ X to use TLS.

In the previous article, we've introduced how to enable SSL/TLS one-way security connection for the EMQ X. This article will introduce how to enable SSL/TLS two-way security connection for MQTT in EMQ X.

The security advantages brought by SSL/TLS

  • Strong certification. When using TLS to establish connections, both communicating parties can check each other's identity. One of the common methods to check identity is that check another party's digital certificate X.509. This kind of digital certificates normally issued by a trusted institution, can not be forged.
  • Ensure the confidentiality. Every session of TLS communicating will be encrypted by the session key which is negotiated by both parties. Any third party will not know the communication content. Although one of the session keys is leaked, it does not affect the security of other sessions.
  • Completeness. It is difficult that tamper the data in encrypted communication and without being discovered.

SSL/TLS protocol

The process of communication in the TLS/SSL protocol consists of two parts. The first part is the handshake protocol. The purpose of this handshake protocol is to identify the identity of another party and establish a safe communication channel. After a handshake, both parties will negotiate the next password suite and session key. The second part is the record protocol. Record is highly similar to other data transmission protocols. It carries content type, version, length, load, etc, and the difference is that the information carried by this protocol is encrypted.

The following picture describes the process of the TLS/SSL handshake protocol. From "hello" of the client until "finished" of the broker. If you are interested in this, you can view more detailed material. Even if you do not know this process, you can also enable this function in EMQ X.


Why do we need SSL/TLS two-way certification

The two-way certification is that a certificate is required for service and client during the connection authentication. Both parties need to perform authentication for ensuring that both sides involved in communication are trusted. Both parties share their public certificates, and then perform verification and confirmation based on the certificate. For some application scenarios that required high security, we need to enable the two-way SSL/TLS authentication.

Preparate of the SSL/TLS certificate

In the two-way certification, we generally use the way self-signed to generate the certificate of the server and client, so this article will take the self-signed certificate as an example.

Generally speaking, we need a digital certificate to ensure the strong certification of TLS communication. The use of digital certificates is a three-party protocol. In addition to the communicating parties, there is a trusted third party to issue the certificate. Sometimes, this trusted third party is a CA. The communicating with CA is usually done by issuing certificates in advance. So, we need a CA’s certificate and an EMQ X’s certificate these two certificates at least, and the EMQ X’s certificate is issued by CA and uses the CA’s certificate to verification.

We assume that your system has installed OpenSSL. Using the toolkit included with OpenSSL can generate the certificate we needed.

Generate the self-signed CA certificate

First, we need a self-signed CA certificate. If you want to generate this certificate, you need a private key to sign it. You can execute the following command to generate this private key:

openssl genrsa -out my_root_ca.key 2048

This command will generate a key with length 2048 and will be stored in my_root_ca.key. If you have this key, you can use it to generate the root certificate of EMQ X:

openssl req -x509 -new -nodes -key my_root_ca.key -sha256 -days 3650 -out my_root_ca.pem

The root certificate is the starting point of an entire chain of trust. If the issuer of each level of a certificate and issuer of the root certificate is trusted, this certificate is trusted. We can use it to issue the certificate for EMQ X.

Generate server certificate

EMQ X also needs its private key to ensure its control for its certificates. The process of generating this private key is similar to the above:

openssl genrsa -out emqx.key 2048

Create file openssl.cnf

  • req_distinguished_name :according to the situation to modify
  • alt_names: modify BROKER_ADDRESS to the real IP or DNS address of EMQ X broker such as IP.1 = or DNS.1 = broker.xxx.com
default_bits  = 2048
distinguished_name = req_distinguished_name
req_extensions = req_ext
x509_extensions = v3_req
prompt = no
countryName = CN
stateOrProvinceName = Zhejiang
localityName = Hangzhou
organizationName = EMQX
commonName = CA
subjectAltName = @alt_names
subjectAltName = @alt_names

Then, use this key and configuration to issue a certificate request:

openssl req -new -key ./emqx.key -config openssl.cnf -out emqx.csr

Then use the root certificate to issue the certificate of EMQ X:

openssl x509 -req -in ./emqx.csr -CA my_root_ca.pem -CAkey my_root_ca.key -CAcreateserial -out emqx.pem -days 3650 -sha256 -extensions v3_req -extfile openssl.cnf

Generate client certificate

Two-way connection authentication also needs to create the certificate of client. First, we need to create client key:

openssl genrsa -out client.key 2048

Using the generated client key to create a client request file:

openssl req -new -key client.key -out client.csr -subj "/C=CN/ST=Zhejiang/L=Hangzhou/O=EMQX/CN=client"

Finally, we use the previously generated CA certificate to sign the client and generate a client certificate:

openssl x509 -req -days 3650 -in client.csr -CA my_root_ca.pem -CAkey my_root_ca.key -CAcreateserial -out client.pem

After preparing the server and client certificate, we can enable TLS/SSL two-way authentication in the EMQ X.

Enable and verify SSL/TLS two-way connection

In the EMQ X, the default listening port of mqtt:ssl is 8883.

EMQ X configuration

Copy the file emqx.pem, emqx.key and my_root_ca.pem generated by OpenSSL tool into the directory etc/certs/ of EMQ X, and refer the following configuration to modify emqx.conf:

## listener.ssl.$name is the IP address and port that the MQTT/SSL
## Value: IP:Port | Port
listener.ssl.external = 8883

## Path to the file containing the user's private PEM-encoded key.
## Value: File
listener.ssl.external.keyfile = etc/certs/emqx.key

## Path to a file containing the user certificate.
## Value: File
listener.ssl.external.certfile = etc/certs/emqx.pem

## Path to the file containing PEM-encoded CA certificates. The CA certificates
## Value: File
listener.ssl.external.cacertfile = etc/certs/my_root_ca.pem

## A server only does x509-path validation in mode verify_peer,
## as it then sends a certificate request to the client (this
## message is not sent if the verify option is verify_none).
## Value: verify_peer | verify_none
listener.ssl.external.verify = verify_peer

MQTT connection test

After finished configuring and restarted EMQ X, we use MQTT client tool - MQTT X (this tool is cross-platform and supports MQTT 5.0) to verify that whether TLS service is normally running.

The requirement of MQTT X version: v1.3.2 or higher version

  • Refer the following picture to create MQTT client in the MQTT X ( in the Host input box need to be replaced by the real IP of EMQ X broker)


At this time, you need to select Self signed in the column Certificate and carry the file my_root_ca.pem generated in the self-signed certificate and the client certificate client.pem and the client key client.key file.

  • Click the button Connect, after connection succeeds, if you can normally perform MQTT publish/subscribe operation, the configuration of SSL two-way connection authentication succeeds.


EMQ X Dashboard verification

Finally, open the Dashboard of EMQ X. On the Listeners page, you can see that there is an mqtt:ssl connection on the port 8883.

So far, we successfully finished the SSL/TLS configuration of the EMQ X Broker and the test of two-way authentication connection.