A secret key of an entity is generated at each key generating agency (center)
by
using divided identification information obtained by dividing identification information
of the entity into a plurality of blocks and a hash value which consists of a plurality
of bits and is set for each key generating agency (center). A plurality of bits
of any order are selected for each key generating agency (center) from an original
hash-value sequence consisting of a predetermined sequence of a plurality of bits
so as to set the hash value for each key generating agency (center). When a new
key generating agency (center) is added to a plurality of existing key generating
agencies (centers), a hash value is set for the new key generating agency (center)
without changing the hash values of the existing key generating agencies (centers).
