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: "batpay a gas efficient protocol for the recurrent micropayment of erc20 tokens"
  Abstract: BatPay is a proxy scaling solution for the transfer of ERC20 tokens. It is suitable for micropayments in one-to-many and few-to-many scenarios, including digital markets and the distribution of rewards and dividends. In BatPay, many similar operations are bundled together into a single transaction in order to optimize gas consumption on the Ethereum blockchain. In addition, some costly verifications are replaced by a challenge game, pushing most of the computing cost off-chain. This results in a gas reduction of the transfer costs of three orders of magnitude, achieving around 1700 transactions per second on the Ethereum blockchain. Furthermore, it includes many relevant features, like meta-transactions for end-user operation without ether, and key-locked payments for atomic exchange of digital goods.

Connected through hyperedge HE-1 (induced by source paper "fair and decentralized exchange of digital goods"):
  with members:
    - "wibsontree efficiently preserving seller s privacy in a decentralized data marketplace"
    - "wibson protocol for secure data exchange and batch payments"

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)