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Recently, concealed data aggregation schemes have been proposed to reduce the transmission cost under maintaining data privacy. Those schemes enhanced security of conventional aggregation through utilizing privacy homo-morphic encryption. The privacy homomorphic encryption provides algebraic computations on ciphertexts directly, e.g., without decryption(More)
In a Universal Mobile Telecommunications System (UMTS), a user equipment (UE) can access IP multimedia services through IP Multimedia Subsystems (IMS). In addition to passing IMS authentication, called IMS AKA, this UE also needs to pass General Packet Radio Service (GPRS) authentication, called 3GPP AKA, since the data of the IMS service is transmitted(More)
Time-bound hierarchical key management mechanisms are widely discussed in several environments and applications. Obviously, the collusion attacks are the serious problems in the time-bound hierarchical key management schemes. In the collusion attacks, two or more users assigned to some classes in distinct time periods collude to compute a key to which they(More)
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