mosquitto-tls - Configure SSL/TLS support for Mosquitto

Roger Light <roger@atchoo.org> Mosquitto Project 08/11/2025 MOSQUITTO-TLS(7)

Generate a certificate authority certificate and key. • openssl req -new -x509 -days <duration> -extensions v3_ca -keyout ca.key -out ca.crt

Generate a client key. • openssl genrsa -aes256 -out client.key 2048 Generate a certificate signing request to send to the CA. • openssl req -out client.csr -key client.key -new Send the CSR to the CA, or sign it with your CA key: • openssl x509 -req -in client.csr -CA ca.crt -CAkey ca.key -CAcreateserial -out client.crt -days <duration>

mosquitto provides SSL support for encrypted network connections and authentication. This manual describes how to create the files needed. Note It is important to use different certificate subject parameters for your CA, server and clients. If the certificates appear identical, even though generated separately, the broker/client will not be able to distinguish between them and you will experience difficult to diagnose errors.

The sections below give the openssl commands that can be used to generate certificates, but without any context. The asciicast at https://asciinema.org/a/201826 gives a full run through of how to use those commands.

mosquitto-tls - Configure SSL/TLS support for Mosquitto

mosquitto(8), mosquitto.conf(5)

Generate a server key. • openssl genrsa -aes256 -out server.key 2048 Generate a server key without encryption. • openssl genrsa -out server.key 2048 Generate a certificate signing request to send to the CA. • openssl req -out server.csr -key server.key -new Note When prompted for the CN (Common Name), please enter either your server (or broker) hostname or domain name. Send the CSR to the CA, or sign it with your CA key: • openssl x509 -req -in server.csr -CA ca.crt -CAkey ca.key -CAcreateserial -out server.crt -days <duration>