I am confused with the certificated associated with the google cloud iot core.
which CA certificate is used at the registry level and how to generate it.
And the "roots.pem" certificate used to communicate between device and cloud iot core using mqtt bridge, which i got from this link 'https://pki.google.com/roots.pem'. Is it different than the one which is associated with the registry level certificate?

I have tried adding roots.pem certificate but it throws an error that file is too big. I have also added public key which is used to authenticate device using public/private key pair it was added successfully. but i get confused which one to use and where to use and how to generate one.

How to verify Device with registry level ca certificates for more security?

I am using following command,

for getting roots.pem certificate
'https://pki.google.com/roots.pem'

for getting public/private key pair

```
openssl req -x509 -nodes -newkey rsa:2048 -keyout rsa_private.pem -days 1000000 -out rsa_cert.pem -subj "/CN=unused"

```