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: "wsemail a retrospective on a system for secure internet messaging based on web services"
  Abstract: Web services offer an opportunity to redesign a variety of older systems to exploit the advantages of a flexible, extensible, secure set of standards. In this work we revisit WSEmail, a system proposed over ten years ago to improve email by redesigning it as a family of web services. WSEmail offers an alternative vision of how IM and email services could have evolved, offering security, extensibility, and openness in a distributed environment instead of the hardened walled gardens that today's rich messaging systems have become. We demonstrate the flexibility of WSEmail using three business use cases: secure channel IM, business workflows with routed forms, and on-demand attachments. Since increased flexibility often mitigates against security and performance, we designed WSEmail with security in mind and formally proved the security of one of its core protocols (on-demand attachments) using the TulaFale and ProVerif automated proof tools. We also provide performance measures for the basic WSEmail functions in a prototype we implemented using .NET. Our experiments show a latency of about a quarter of a second per transaction under load.

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.NI(Networking and Internet Architecture)