This paper examines the sharing of risks between generations in the framework of an overlapping generations model of social security with shocks to the productivity of labor and capital and demographic shocks. The study focused on stationary long run allocations. The concept of interim optimality was utilized, which amounts to standard Pareto optimality once the state of the world in which the agents are born is known. The set of interim optimal allocations was characterized and the equilibria associated with various institutional forms of social security from the point of view of the optimal criterion were also studied. In addition, the analogs of two traditional welfare theorems of microeconomic theory were obtained.