A cryptographic scheme can be used for controlling access to information, since any user who does not have a proper key can not decipher. But for this purpose, a user would have to manage a huge number of keys when he tries to communicate with a lot of people. The practical utilization method of access control by cryptography is discussed. The authors propose a typical organizational structure called hierarchical group oriented structure and go on to propose a hierarchical group oriented key management method (HGK method) based on the multiple keys generated from the combination of pieces. They explain that this method is very desirable in terms of reducing the numbers of keys required for each user in the hierarchical group oriented structure.
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