ValueError: invalid key when connecting to AWS IoT Core with umqtt (Micropython) - mqtt

Question

A few days ago I bought a Raspberry Pi Pico W and I am trying to connect it to AWS Iot Core. However, I get stuck when connecting to AWS.
I have gone throught the following steps:
installed Micropython on the Raspberry Pi Pico W, this works!
Created an AWS account.
registered a "Thing" at IoT Core
Downloaded the corresponding certificates & keys: (Certificates: AmazonRootCA1.pem, certificate.pem.crt, Keys: public.pem.key & private.pem.key)
created a policy, which allows the policy all actions. At AWS this policy is activated and has the form:
{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Action": "*",
"Resource": "*"
}
]
}
Attached the certificate to the policy.
Attached the registered Thing to the policy.
transfered the keys and the certificates to the Raspberry Pi Pico W.
Hereafter, I use Thonny to write the following code trying to connect the raspberry pi with AWS.
import time
import network
import urequests
SSID = "XXXX"
PASSWORD = "XXXX"
print("start connecting")
wlan = network.WLAN(network.STA_IF)
wlan.active(True)
wlan.connect(SSID, PASSWORD)
print("Connected:", wlan.isconnected())
import sys
import machine
import argparse
from umqtt.simple import MQTTClient
clientId = 'client1'
AWS_ENDPOINT = 'XXXXX.amazonaws.com'
PORT = 8883
certfile = '/certificate.pem.crt'
with open(certfile, 'r') as f:
cert = f.read()
keyfile = '/private.pem.key'
with open(keyfile, 'r') as f:
key = f.read()
print("Key and Certificate files Loaded")
SSL_PARAMS = {'key': key, 'cert': cert, 'server_side': False}
client = MQTTClient(clientId, AWS_ENDPOINT, port=PORT, keepalive=10000, ssl=True, ssl_params=SSL_PARAMS)
print("Client created")
client.connect()
The program runs until:
client.connect()
And gives me the following error:
Traceback (most recent call last):
File "<stdin>", line 38, in <module>
File "/lib/umqtt/simple.py", line 61, in connect
ValueError: invalid key
(line 38 being the client.connect() statement)
The format of the private.pem.key is:
-----BEGIN RSA PRIVATE KEY-----
[block of characters]
-----END RSA PRIVATE KEY-----
I there anyone who knows what I am doing wrong? Thank you in advance for the help!! :)
Kind regards, Benjamin

Answer 1

Sorry - late to the party.
If you haven't got this working you should try to convert the key & cert files to .DER format with OpenSSL
openssl x509 -in certificate.pem.crt -out certificate.der -outform DER
openssl rsa -in private.pem.key -out private.key.der -outform DER
`certfile = '/certificate.der'`
`with open(certfile, 'r') as f:`
`cert = f.read()`
`keyfile = '/private.pem.der'`
`with open(keyfile, 'r') as f:`
`key = f.read()`