It makes use of a trusted third party authentication known as `` key distribution center ( KDC ) '' , which consists of two logically separate parts : an Authentication Server ( AS ) and a Ticket Granting Server ( TGS ) . It makes use of a trusted third party , termed a key distribution center ( KDC ) , which consists of two logically separate parts : an Authentication Server ( AS ) and a Ticket Granting Server ( TGS ) .