.der certificate. What is needed and how to install?

Question

Cryptography

I install VPN ikev2 on my phone. The VPN provider (the one that made the proton mail from CERN) asks to install the certificatename.der certificate. I'm completely new to certificates, it's a dark forest for me. But I often met articles (including on Habré) that installing a certificate jeopardizes the security of all traffic and that the one whose certificate is installed can read all traffic, including encrypted.
In this regard, the question is: what kind of certificate is this .der, how safe / dangerous is it to install such a certificate?

Answer 1

DER is an ASN.1 binary notation format, and ASN.1 is a notation standard that describes data structures for representing, encoding, transmitting, and decoding data.
What matters is not what format the certificate is in, but who its publisher is. The question is more correct to put like this: "Should I trust Proton Technologies?" And this question already applies not only to installing a certificate on a mobile phone, but also to the willingness to use a VPN or a mail service from this provider.

Answer 2

Not safe from the word "wow".