Support for MQTT with TLS/SSL on ESP32

[djs0109]

Hi everyone,

I am trying to use MQTTs on ESP32. Since I am relatively new to TLS/SSL, I am very appreciative for any experience or suggestion from you!

My ultimate goal is to connect my ESP32 to the MQTT broker of our enterprise mqtt.n5geh.eonerc.rwth-aachen.de, which is set up by someone else and requires Encryption.

As the first try, I have managed to connect to the public encrypted MQTT Broker test.mosquitto.org 8883 with the following code

client_id = "jdu-esp32-test"
client = MQTTClient(client_id, "test.mosquitto.org", 8883, user=None, password=None, keepalive=30, ssl=True, ssl_params={})
client.connect()

However, with the same code (the only difference is that I must provide user and password here), I cannot connect to our MQTT endpoint. Here is the error message:

File "umqtt/simple.py", line 72, in connect
OSError: (-17040, 'MBEDTLS_ERR_RSA_PUBLIC_FAILED+MBEDTLS_ERR_MPI_ALLOC_FAILED')

I have tried several workarounds, but none of them solve my problem.

I also find another discussion #9259. But when I try to use the solution provided by Carglglz https://github.com/orgs/micropython/discussions/9259#discussioncomment-3612105, I find that ussl has no attributes named CERT_REQUIRED.

Version: MicroPython v1.19.1 on 2022-06-18; ESP32 module with ESP32

[djs0109]

I found a same similar here https://stackoverflow.com/questions/68481716/micropython-https-request-blocks-further-requests.

So the problem was, I am running out of RAM. When I only run a simple test script on my board, it works. I post my code below:

user = b"........"  # use binary is import! otherwise wont work
password_mqtt = b"........"
topic = ".../.../.../"

ssl_params = {}

client = MQTTClient(client_id,
                    host,
                    port,
                    user=user, password=password_mqtt,
                    keepalive=30, ssl=True, ssl_params=ssl_params)
client.connect()
while True:
    client.publish(topic,
                   json.dumps({"temp": 10})
                   )
    time.sleep(1)

My experience is, the ssl_params can be just left to default. And it is important to use binary strings for user and password :)