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: "interactive proof of stake"
  Abstract: The paper examines decentralized cryptocurrency protocols that are based on the use of internal tokens as identity tools. An analysis of security problems with popular Proof-of-stake consensus protocols is provided. A new protocol, Interactive Proof-of-stake, is proposed. The main ideas of the protocol are to reduce a number of variables a miner can iterate over to a minimum and also to bring a communication into block generation. The protocol is checked against known attacks. It is shown that Interactive Proof-of-stake is more secure than current pure Proof-of-stake protocols.

Connected through hyperedge HE-1 (induced by source paper "betting on blockchain consensus with fantomette"):
  with members:
    - "optimal selfish mining strategies in bitcoin"
    - "the miner s dilemma"
    - "beyond nash equilibrium solution concepts for the 21st century"

Connected through hyperedge HE-2 (induced by source paper "winning the caucus race continuous leader election via public randomness"):
  with members:
    - "centrally banked cryptocurrencies"

Connected through hyperedge HE-3 (induced by source paper "consensus in the age of blockchains"):
  with members:
    - "implicit consensus blockchain with unbounded throughput"
    - "blockchains consensus protocols in the wild"
    - "chainspace a sharded smart contracts platform"
    - "practical synchronous byzantine consensus"
    - "blockbench a framework for analyzing private blockchains"
    - "enhancing bitcoin security and performance with strong consistency via collective signing"
    - "service oriented sharding with aspen"
    - "non determinism in byzantine fault tolerant replication"

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)