1.1.7 - TGS (Ticket Granting Server)
The second major service is the Ticket Granting Server, which is the service that delivers tickets for all the managed services to the users.
A client can access to this service fater having been authenticated - ie, after having received a ticket allowing it to access the TGS from the AS -.
At this point, all the exchanges are encrypted using the user session key.
Ther is not too much to tell about this service, except that ach request sent by the client contains the targeted service principal name, and the ticket issued by the AS.
How it works ?
When the TGS receives a request, it will read the ticket contained in the request, and will validate it. If the ticket has been issued by the AS, then the TGS has the AS secret key and can decrypt the ticket, otherwise it's potentially a forged ticket, and it will be discarded.
The TGS then generate a ticket for the targted service, and enncryt it using the service's secret key, then encapsulate this encypted ticket into a response which will be itself encrypted using the client's secret key.
The client will receive this response, will decrypt it and extract the encypted ticket, and will send this encrypted ticket to the targeted service, which will be able to decrypt it and validate it.
Of course, in the mean time, many checks will be done relative to the ticket validity, so one can be assured that the service is only accessible by those with the credential to do so.