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: "a robust and efficient node authentication protocol for mobile ad hoc networks"
  Abstract: A mobile ad hoc network (MANET) is a collection of mobile nodes that communicate with each other by forming a multi-hop radio network. Security remains a major challenge for these networks due to their features of open medium, dynamically changing topologies, reliance on cooperative algorithms, absence of centralized monitoring points, and lack of clear lines of defense. Design of an efficient and reliable node authentication protocol for such networks is a particularly challenging task since the nodes are battery-driven and resource constrained. This paper presents a robust and efficient key exchange protocol for nodes authentication in a MANET based on multi-path communication. Simulation results demonstrate that the protocol is effective even in presence of large fraction of malicious nodes in the network. Moreover, it has a minimal computation and communication overhead that makes it ideally suitable for MANETs.

Connected through hyperedge HE-1 (induced by source paper "security and privacy issues in wireless mesh networks a survey"):
  with members:
    - "secure and privacy preserving authentication protocols for wireless mesh networks"
    - "reputation and trust based systems for wireless self organizing networks"
    - "secure and privacy aware searching in peer to peer networks"
    - "an efficient and user privacy preserving routing protocol for wireless mesh networks"
    - "a distributed protocol for detection of packet dropping attack in mobile ad hoc networks"
    - "cross layer protocols for multimedia communications over wireless networks"
    - "secure routing in wireless mesh networks"
    - "a survey on wireless sensor network security"

Connected through hyperedge HE-2 (induced by source paper "secure and privacy preserving authentication protocols for wireless mesh networks"):
  with members:
    - "reputation and trust based systems for wireless self organizing networks"
    - "secure routing in wireless mesh networks"
    - "a survey on wireless sensor network security"
    - "a distributed trust and reputation framework for mobile ad hoc 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)