Place the graham crackers in a food processor with the sugar, salt and soft butter- mix until all of the ingredients are incorporated. Put the graham cracker crumb mixture in a spring-form, or 9-inch cake pan and work the crust mixture to the edges. For the filling: Place the cream cheese, cocoa powder, sugar, vanilla, eggs and salt in a mixing bowl and blend for 3 minutes, or until the batter is smooth. Place the batter in the pan over the graham cracker crust and bake at 350 degrees for 1 hour, or until an inserted toothpick comes out clean. Refrigerate for three hours before cutting.