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: "optimal power allocation and secrecy sum rate in two way untrusted relaying"
  Abstract: In this paper, we examine the secrecy performance of two-way relaying between a multiple antenna base station (BS) and a single antenna mobile user (MU) in the presence of a multiple antenna friendly jammer (FJ). We consider the untrusted relaying scenario where an amplify-and-forward relay is both a necessary helper and a potential eavesdropper. To maximize the instantaneous secrecy sum rate, we derive new closed-form solutions for the optimal power allocation (OPA) between the BS and MU under the scenario of relaying with friendly jamming (WFJ). Based on the OPA solution, new closed-form expressions are derived for the ergodic secrecy sum rate (ESSR) with Rayleigh fading channel. Furthermore, we explicitly determine the high signal-to-noise ratio slope and power offset of the ESSR to highlight the benefits of friendly jamming. Numerical examples are provided to demonstrate the impact of the FJ's location and number of antennas on the secrecy performance.

Connected through hyperedge HE-1 (induced by source paper "optimal power allocation by imperfect hardware analysis in untrusted relaying networks"):
  with members:
    - "joint relay selection and power allocation in large scale mimo systems with untrusted relays and passive eavesdroppers"
    - "analysis and design of secure massive mimo systems in the presence of hardware impairments"
    - "physical layer security for massive mimo systems impaired by phase noise"
    - "joint relay and jammer selection improves the physical layer security in the face of csi feedback delays"
    - "optimum wirelessly powered relaying"
    - "physical layer security for massive mimo an overview on passive eavesdropping and active attacks"
    - "massive mimo systems with non ideal hardware energy efficiency estimation and capacity limits"
    - "massive mimo for next generation wireless systems"

Connected through hyperedge HE-2 (induced by source paper "energy harvesting based secure two way communication using an untrusted relay"):
  with members:
    - "joint relay selection and power allocation in large scale mimo systems with untrusted relays and passive eavesdroppers"
    - "joint relay and jammer selection improves the physical layer security in the face of csi feedback delays"
    - "wireless powered relays in cooperative communications time switching relaying protocols and throughput analysis"
    - "secure communication via a wireless energy harvesting untrusted relay"
    - "security versus reliability analysis of opportunistic relaying"
    - "secure communication with a wireless powered friendly jammer"
    - "secure beamforming for mimo two way communications with an untrusted relay"

Connected through hyperedge HE-3 (induced by source paper "secure two way communication via a wireless powered untrusted relay and friendly jammer"):
  with members:
    - "wireless powered relays in cooperative communications time switching relaying protocols and throughput analysis"
    - "secure communication via a wireless energy harvesting untrusted relay"
    - "wireless networks with rf energy harvesting a contemporary survey"
    - "secure communication with a wireless powered friendly jammer"
    - "a new look at dual hop relaying performance limits with hardware impairments"

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)