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: "blockchain based grid operation services for transactive energy systems"
  Abstract: Transactive Energy Systems (TES) are modern electric power systems that enable decentralized owners of power generation assets to engage in energy transactions and provide computing services that improve the performance of power system operation. Blockchain technology is a key enabler of TES, allowing peers to engage in trustless, persistent transactions that are both enforceable and auditable. However, previous work within this context has not adequately explored fraudulent service transactions amongst peers, and its potential negative impact on power system operation. To that end, this paper proposes a blockchain based TES that enables distributed peers (known as agents), to receive incentives for providing grid operation services in the form of voltage regulation, which is a critical operational service. The proposed system i) maintains a trustless reputation rating for each agent that is increased proportionately with each transaction that improves grid operation, ii) utilizes smart contracts to enforce the validity of each transaction and penalizes reputation ratings in case of a fraudulent transaction, iii) automates the negotiation and bidding of agent services by implementing the contract net protocol (CNP) as a smart contract. Experimental results on both simulated and real-world power systems are executed to demonstrate the efficacy of the proposed system.

Connected through hyperedge HE-1 (induced by source paper "blockchain for future smart grid a comprehensive survey"):
  with members:
    - "exploring the attack surface of blockchain a systematic overview"
    - "an efficient blockchain based hierarchical authentication mechanism for energy trading in v2g environment"
    - "when energy trading meets blockchain in electrical power system the state of the art"
    - "energy crowdsourcing and peer to peer energy trading in blockchain enabled smart grids"
    - "blockchain technologies for smart energy systems fundamentals challenges and solutions"
    - "key management systems for smart grid advanced metering infrastructure a survey"
    - "a survey on the security of blockchain systems"
    - "a survey on security and privacy issues of bitcoin"

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)