pA 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./p [WO2007149850A2]
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