Certificates are used to authenticate you to web services at MIT. Some sites use certificates directly and others as a way to authenticate with our Touchstone Authentication system. Certificates are a safe way for our web applications to identify you without you needing to type in your Kerberos username and password. Certificates expire once per year, creating the need to renew them at least this often. They must be installed on each browser for each device that you plan on using to access certificate-protected sites.