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: "towards secure and efficient payment channels"
  Abstract: Micropayment channels are the most prominent solution to the limitation on transaction throughput in current blockchain systems. However, in practice channels are risky because participants have to be online constantly to avoid fraud, and inefficient because participants have to open multiple channels and lock funds in them. To address the security issue, we propose a novel mechanism that involves watchtowers incentivized to watch the channels and reveal a fraud. Our protocol does not require participants to be online constantly watching the blockchain. The protocol is secure, incentive compatible and lightweight in communication. Furthermore, we present an adaptation of our protocol implementable on the Lightning protocol. Towards efficiency, we examine specific topological structures in the blockchain transaction graph and generalize the construction of channels to enable topologies better suited to specific real-world needs. In these cases, our construction reduces the required amount of signatures for a transaction and the total amount of locked funds in the system.

Connected through hyperedge HE-1 (induced by source paper "congestion attacks in payment channel networks"):
  with members:
    - "concurrency and privacy with payment channel networks"
    - "privacy utility tradeoffs in routing cryptocurrency over payment channel networks"
    - "hijacking routes in payment channel networks a predictability tradeoff"
    - "topological analysis of bitcoin s lightning network"
    - "discharged payment channels quantifying the lightning network s resilience to topology based attacks"
    - "sprites and state channels payment networks that go faster than lightning"

Connected through hyperedge HE-2 (induced by source paper "fail safe watchtowers and short lived assertions for payment channels"):
  with members:
    - "concurrency and privacy with payment channel networks"
    - "teechain a secure asynchronous blockchain payment network"
    - "bitcoin ng a scalable blockchain protocol"

Connected through hyperedge HE-3 (induced by source paper "brick asynchronous payment channels"):
  with members:
    - "enhancing bitcoin security and performance with strong consistency via collective signing"
    - "bitcoin meets strong consistency"

Connected through hyperedge HE-4 (induced by source paper "discharged payment channels quantifying the lightning network s resilience to topology based attacks"):
  with members:
    - "topological analysis of bitcoin s lightning network"
    - "decentralization in bitcoin and ethereum networks"
    - "towards a concurrent and distributed route selection for payment channel networks"
    - "settling payments fast and private efficient decentralized routing for path based transactions"
    - "teechan payment channels using trusted execution environments"

Connected through hyperedge HE-5 (induced by source paper "brick asynchronous state channels"):
  with members:
    - "validated asynchronous byzantine agreement with optimal resilience and asymptotically optimal time and word communication"
    - "chainspace a sharded smart contracts platform"
    - "enhancing bitcoin security and performance with strong consistency via collective signing"
    - "bitcoin meets strong consistency"

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)