FIELD: information technology.;SUBSTANCE: security system for a hierarchical network includes L hierarchical levels each corresponding to a security domain, wherein the system comprises: a plurality of local network nodes; a keying material generator which generates correlated sets of keying material for each network node, wherein each keying material set includes L keying material sub-sets, each corresponding to an associated security domain; and a setup server which distributes the generated keying material sets to each network node to enable the network nodes to communicate with one another in a security domain of a hierarchical level k by using a corresponding sub-set of keying material, wherein the network nodes communicate with one another via at least a normal communication mode and an unusual communication mode, wherein the normal communication mode is implemented when the lowest common security domain is the lowest level security domain L, and unusual communication mode is implemented when the lowest common security domain is a security domain of a higher level than the lowest level security domain L.;EFFECT: high information security.;19 cl, 4 dwg
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