Are there security risks in exposing a certificate?

Question

1. If an attacker would have access to a certificate, could he build an attack out of that?

or rephrasing it:

How could an attacker profit from a device certificate, that he gets his hands on?

For example: A certificate that is used for a device (IoT-Device) gets public, which is in my mind part of the idea of using it, could an attacker profit from that? For example clone it for a different device. Deleting or making the certificate invalid is not an attack in scope in this scenario.

Assumption is:

• the private-key is still safe
• the CA oder ICA that signed the certificate is valid and secure
• Data in the certificate is not confidential, but there is an ID for the device
• the attacker is in possession of the certificate file

And following out of that question, if the answer is no, there is no threat.

2. I could store the certificate on the device, without thinking to much about security (except deletion and changes that lead to invalid behavior)?

Answer 1

In a PKI (public key infrastructure) scenario, there is no harm in exposing the certificate - in fact it is necessary to expose the certificate in a PKI scenario. This is because the certificate contains the public keys of the server that you are creating the secure connection with. Moreover, the certificate contains information about the party that operates this server, so that you can be sure that they 'are who they say they are' when you connect to the server. This information is verified by a trusted third party certificate authority (CA), and the certificate is signed by the CA.

As an example, if you go to any secure web site (such as security.stackexchange.com or www.bankofamerica.com), you can easily view the site's certificate in your web browser by clicking on the padlock to the left of your address bar, then following these steps.

Now, in addition to the certificate, the server must have the private key that corresponds to the public key in the certificate. The private key must not be exposed. If it is, then anyone with the private key can impersonate the server or eavesdrop on a connection with the server.

However, the certificate is of no use to an attacker, if the attacker does not have the private key that corresponds to the public key in the certificate. See Could a stolen certificate show as trusted? for more info.