A security system for a hierarchical network (10) includes L hierarchical levels each corresponding to a security domain level (16), and a plurality of local network nodes (A, B, . . . , Z). A keying material generator (24) generates a set (30) of correlated keying material for each network node. Each set (30) of keying material is composed of L sub-sets (32) of keying material one for each security domain level (16). A set up server (34) distributes the generated sets (30) of keying material to each network node (A, B, . . . , Z) to enable the network nodes (A, B, . . . , Z) to communicate with one another at a security domain of a hierarchical level k by a use of a corresponding sub-set (32) of the security keying material.