One method of establishing this trust is through a certificate, an electronic document verifying that entities or persons are who they claim to be.
A certificate is issued to an entity by a third party that is trusted by both of the other parties.
I have a user where SSL sites suddenly started throwing up certificate errors.
One of the sites that was failing, I manually installed the root certificate from digicert website.
If you want to check whether your domain policy allow you to install certificate to Trusted Root Certification Authority, when importing the cert via manually select the store and tick 'Show physical stores'.
For these operating systems and devices, customers do not need to take any action as these systems and devices will be automatically protected.
The other key, known as the public key, is intended to be shared with the world.
However, there must be a way for the owner of the key to tell the world who the key belongs to. A digital certificate is a tamperproof piece of data that packages a public key together with information about it (who owns it, what it can be used for, when it expires, and so forth). Certificates are used primarily to verify the identity of a person or device, authenticate a service, or encrypt files.
Normally you won’t have to think about certificates at all.
You might, however, see a message telling you that a certificate is expired or invalid.