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: "a new covert channel over cellular voice channel in smartphones"
  Abstract: Investigating network covert channels in smartphones has become increasingly important as smartphones have recently replaced the role of traditional computers. Smartphones are subject to traditional computer network covert channel techniques. Smartphones also introduce new sets of covert channel techniques as they add more capabilities and multiple network connections. This work presents a new network covert channel in smartphones. The research studies the ability to leak information from the smartphones applications by reaching the cellular voice stream, and it examines the ability to employ the cellular voice channel to be a potential medium of information leakage through carrying modulated speech-like data covertly. To validate the theory, an Android software audio modem has been developed and it was able to leak data successfully through the cellular voice channel stream by carrying modulated data with a throughput of 13 bps with 0.018% BER. Moreover, Android security policies are investigated and broken in order to implement a user-mode rootkit that opens the voice channels by stealthily answering an incoming voice call. Multiple scenarios are conducted to verify the effectiveness of the proposed covert channel. This study identifies a new potential smartphone covert channel, and discusses some security vulnerabilities in Android OS that allow the use of this channel demonstrating the need to set countermeasures against this kind of breach.

Connected through hyperedge HE-1 (induced by source paper "no free charge theorem a covert channel via usb charging cable on mobile devices"):
  with members:
    - "a study on power side channels on mobile devices"
    - "pin skimming exploiting the ambient light sensor in mobile devices"

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)