SSL Load Cert Chain "Invalid Key"

[AngeloFatica]

Hello, I have been using micropython to connect to MQTT for a couple of years now using the mqtt.simple library file. Upon a fresh build, it seems the SSL parameters have changed and I cannot use the same certs I have been using to connect. I keep getting an invalid key error when using my certs now. Is there a change to the SSL library that happened recently?

Before, I was using a pico for most of the time with the same libraries, but have also used an stm32 to connect previously as well. Any help is appreciated here, thank you.

I have been using DER format CERTS for a while now, so not sure why it is behaving differently now. My ssl is version 0.2.1.

Traceback (most recent call last):
File "main.py", line 344, in
File "/flash/lib/umqtt/simple.py", line 61, in connect
File "ssl.py", line 1, in wrap_socket
File "ssl.py", line 1, in load_cert_chain
ValueError: invalid key
MicroPython v1.24.0-preview.17.gd8039ee1d.dirty on 2025-10-24; NUCLEO_H743ZI with STM32H743

[AngeloFatica]

My error was trying to use client and key certs as well as the ca cert files. This worked previously for me but my latest build I deleted the client and key certs and kept only the ca.der file in my connection and that has fixed the issue.