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: "the sybil attacks and defenses a survey"
  Abstract: In this paper we have a close look at the Sybil attack and advances in defending against it, with particular emphasis on the recent work. We identify three major veins of literature work to defend against the attack: using trusted certification, using resources testing, and using social networks. The first vein of literature considers defending against the attack using trusted certification, which is done by either centralized certification or distributed certification using cryptographic primitives that can replace the centralized certification entity. The second vein of literature considers defending against the attack by resources testing, which can by in the form of IP testing, network coordinates, recurring cost as by requiring clients to solve puzzles. The third and last vein of literature is by mitigating the attack combining social networks used as bootstrapping security and tools from random walk theory that have shown to be effective in defending against the attack under certain assumptions. Our survey and analyses of the different schemes in the three veins of literature show several shortcomings which form several interesting directions and research questions worthy of investigation.

Connected through hyperedge HE-1 (induced by source paper "resource competitive sybil defenses"):
  with members:
    - "proof of work without all the work"
    - "secure one way interactive communication"
    - "torbricks blocking resistant tor bridge distribution"
    - "interactive communication with unknown noise rate"
    - "bitcoin ng a scalable blockchain protocol"
    - "the mason test a defense against sybil attacks in wireless networks without trusted authorities"
    - "self healing computation"
    - "quorums quicken queries efficient asynchronous secure multiparty computation"

Connected through hyperedge HE-2 (induced by source paper "proof of work without all the work computationally efficient attack resistant systems"):
  with members:
    - "proof of work without all the work"
    - "secure one way interactive communication"
    - "torbricks blocking resistant tor bridge distribution"
    - "interactive communication with unknown noise rate"
    - "the mason test a defense against sybil attacks in wireless networks without trusted authorities"
    - "self healing computation"
    - "storage and search in dynamic peer to peer networks"
    - "making evildoers pay resource competitive broadcast in sensor networks"

Connected through hyperedge HE-3 (induced by source paper "proof of work without all the work"):
  with members:
    - "algorand the efficient and democratic ledger"
    - "bitcoin ng a scalable blockchain protocol"
    - "the mason test a defense against sybil attacks in wireless networks without trusted authorities"
    - "sybilcontrol practical sybil defense with computational puzzles"
    - "uncovering social network sybils in the wild"
    - "breaking the o n 2 bit barrier scalable byzantine agreement with an adaptive adversary"

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)