Certificates are added to the keychain. Expired or revoked certificates remain in the keychain, e.g. to maintain access to older, encrypted emails. When the computer is set up and set up again, all previous, old certificates should also be installed.

1. Click the file (PKCS12 format) that contains the key and the certificate.
    

   

   
    
2. Select "login" for keychain and click "Add".
    

   

   
    
3. When prompted for the certificate password, enter the password and click "OK".
    

   

   
    
4. After the installation you will be redirected to the Keychain Access. There you can see the certificate you just installed under "My Certificates".