All authentication requests are routed through the centralized Kerberos server. Trusted third-party Kerberos works through a centralized authentication server that all systems on the network inherently trust. After a user is authenticated through Kerberos at the start of a login session, their credentials are transparently passed to every resource that they access during the day. Single sign-on End users only need to log in once to access all network resources that support Kerberos authentication. Secure Kerberos is secure because it does not transmit passwords over the network in clear text. Kerberos provides a secure, single sign-on, trusted third-party, mutual authentication service. Benefits of using Kerberos authentication By leveraging the Mac OS X Kerberos service, Outlook for Mac uses the single sign-on mechanism to offer better password handling and a cleaner setup experience. Mac OS X includes built-in support for Microsoft Kerberos authentication and Active Directory authentication policies, such as password changes, expiration and forced password changes, and Active Directory replication and failover. To use this ticketing scheme, both the client and the server must have a trusted connection to the domain Key Distribution Center (KDC).

The client can use the same ticket on the network to request other network resources. If an attacker tries to capture and decrypt the information in a ticket, the breach will be limited to the current session. The timestamp included in the ticket indicates that it's a recently generated ticket and is not a replay attack. This decrypted ticket indicates the proof of the client's identity and is used to authenticate the client.

If the client successfully decrypts the ticket, it keeps the ticket, which is now shared by the client and the server. The client then attempts to decrypt the ticket by using its password. Then, the authentication server grants the client encrypted tickets that include client information and the session key that expires after a specified period of time. In this scheme, a client must provide a valid user name and password only once to prove their identity to an authentication server. Kerberos protocol uses cryptography to help provide secure mutual authentication for a network connection between a client and a server, or between two servers.

Outlook 2016 for Mac supports Kerberos protocol as a method of authentication with Microsoft Exchange Server and standalone LDAP accounts.

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