human: Given a node-centered hypergraph: <hypergraph>, where nodes represent papers and hyperedges represent sets of papers co-cited by a source paper.

Details of the hypergraph:
Center node: "an attack on privacy preserving data aggregation protocol for wireless sensor networks"
  Abstract: In-network data aggregation in Wireless Sensor Networks (WSNs) provides efficient bandwidth utilization and energy-efficient computing.Supporting efficient in-network data aggregation while preserving the privacy of the data of individual sensor nodes has emerged as an important requirement in numerous WSN applications. For privacy-preserving data aggregation in WSNs, He et al. (INFOCOM 2007) have proposed a Cluster-based Private Data Aggregation (CPDA) that uses a clustering protocol and a well-known key distribution scheme for computing an additive aggregation function in a privacy-preserving manner. In spite of the wide popularity of CPDA, it has been observed that the protocol is not secure and it is also possible to enhance its efficiency. In this paper, we first identify a security vulnerability in the existing CPDA scheme, wherein we show how a malicious participant node can launch an attack on the privacy protocol so as to get access to the private data of its neighboring sensor nodes. Next it is shown how the existing CPDA scheme can be made more efficient by suitable modification of the protocol. Further, suitable modifications in the existing protocol have been proposed so as to plug the vulnerability of the protocol.

Connected through hyperedge HE-1 (induced by source paper "homomorphic encryption theory and application"):
  with members:
    - "security in wireless sensor networks"
    - "security and privacy issues in wireless mesh networks a survey"
    - "secure and privacy preserving data aggregation protocols for wireless sensor networks"
    - "secure and privacy preserving authentication protocols for wireless mesh networks"
    - "a novel mechanism for detection of distributed denial of service attacks"
    - "a mechanism for detection of gray hole attack in mobile ad hoc networks"
    - "reputation and trust based systems for wireless self organizing networks"
    - "secure and privacy aware searching in peer to peer networks"

Connected through hyperedge HE-2 (induced by source paper "secure and privacy preserving data aggregation protocols for wireless sensor networks"):
  with members:
    - "reputation and trust based systems for wireless self organizing networks"
    - "internet of things applications and challenges in technology and standardization"
    - "a robust and secure aggregation protocol for wireless sensor networks"
    - "a trust based detection algorithm of selfish packet dropping nodes in a peer to peer wireless mesh network"
    - "a survey on wireless sensor network security"
    - "a distributed trust and reputation framework for mobile ad hoc networks"
    - "medians and beyond new aggregation techniques for sensor networks"

Question: Please tell me which class the center node belongs to. The 40 classes are: cs.NA(Numerical Analysis), cs.MM(Multimedia), cs.LO(Logic in Computer Science), cs.CY(Computers and Society), cs.CR(Cryptography and Security), cs.DC(Distributed, Parallel, and Cluster Computing), cs.HC(Human-Computer Interaction), cs.CE(Computational Engineering, Finance, and Science), cs.NI(Networking and Internet Architecture), cs.CC(Computational Complexity), cs.AI(Artificial Intelligence), cs.MA(Multiagent Systems), cs.GL(General Literature), cs.NE(Neural and Evolutionary Computing), cs.SC(Symbolic Computation), cs.AR(Hardware Architecture), cs.CV(Computer Vision and Pattern Recognition), cs.GR(Graphics), cs.ET(Emerging Technologies), cs.SY(Systems and Control), cs.CG(Computational Geometry), cs.OH(Other Computer Science), cs.PL(Programming Languages), cs.SE(Software Engineering), cs.LG(Machine Learning), cs.SD(Sound), cs.SI(Social and Information Networks), cs.RO(Robotics), cs.IT(Information Theory), cs.PF(Performance), cs.CL(Computation and Language), cs.IR(Information Retrieval), cs.MS(Mathematical Software), cs.FL(Formal Languages and Automata Theory), cs.DS(Data Structures and Algorithms), cs.OS(Operating Systems), cs.GT(Computer Science and Game Theory), cs.DB(Databases), cs.DL(Digital Libraries), cs.DM(Discrete Mathematics). Directly output the class name.

gpt: cs.CR(Cryptography and Security)