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: "secret key agreement with large antenna arrays under the pilot contamination attack"
  Abstract: We present a secret key agreement (SKA) protocol for a multi-user time-division duplex system where a base-station (BS) with a large antenna array (LAA) shares secret keys with users in the presence of non-colluding eavesdroppers. In the system, when the BS transmits random sequences to legitimate users for sharing common randomness, the eavesdroppers can attempt the pilot contamination attack (PCA) in which each of eavesdroppers transmits its target user's training sequence in hopes of acquiring possible information leak by steering beam towards the eavesdropper. We show that there exists a crucial complementary relation between the received signal strengths at the eavesdropper and its target user. This relation tells us that the eavesdropper inevitably leaves a trace that enables us to devise a way of measuring the amount of information leakage to the eavesdropper even if PCA parameters are unknown. To this end, we derive an estimator for the channel gain from the BS to the eavesdropper and propose a rate-adaptation scheme for adjusting the length of secret key under the PCA. Extensive analysis and evaluations are carried out under various setups, which show that the proposed scheme adequately takes advantage of the LAA to establish the secret keys under the PCA.

Connected through hyperedge HE-1 (induced by source paper "data aided secure massive mimo transmission under the pilot contamination attack"):
  with members:
    - "a survey of physical layer security techniques for 5g wireless networks and challenges ahead"
    - "pilot spoofing attack by multiple eavesdroppers"
    - "multiple antennas secure transmission under pilot spoofing and jamming attack"
    - "secure transmission with large numbers of antennas and finite alphabet inputs"
    - "massive mimo pilot decontamination and channel interpolation via wideband sparse channel estimation"
    - "analysis and design of secure massive mimo systems in the presence of hardware impairments"
    - "performance limits of massive mimo systems based on bayes optimal inference"
    - "secure massive mimo transmission with an active eavesdropper"

Connected through hyperedge HE-2 (induced by source paper "a survey of physical layer security techniques for 5g wireless networks and challenges ahead"):
  with members:
    - "secure massive mimo systems with limited rf chains"
    - "secure transmission with large numbers of antennas and finite alphabet inputs"
    - "probabilistically robust swipt for secrecy misome systems"
    - "exploiting full duplex receivers for achieving secret communications in multiuser miso networks"
    - "full duplex bidirectional secure communications under perfect and distributionally ambiguous eavesdropper s csi"
    - "safeguarding decentralized wireless networks using full duplex jamming receivers"
    - "physical layer security aware routing and performance tradeoffs in ad hoc networks"
    - "hybrid procoder and combiner design for secure transmission in mmwave mimo systems"

Connected through hyperedge HE-3 (induced by source paper "cell free massive mimo networks optimal power control against active eavesdropping"):
  with members:
    - "on the total energy efficiency of cell free massive mimo"
    - "mimo beamforming for secure and energy efficient wireless communication"
    - "energy efficiency in cell free massive mimo with zero forcing precoding design"
    - "mimo secret communications against an active eavesdropper"
    - "cell free massive mimo versus small cells"
    - "cell free massive mimo uniformly great service for everyone"
    - "secure massive mimo transmission with an active eavesdropper"
    - "physical layer security for massive mimo an overview on passive eavesdropping and active attacks"

Connected through hyperedge HE-4 (induced by source paper "data aided secure massive mimo transmission with active eavesdropping"):
  with members:
    - "secure transmission with large numbers of antennas and finite alphabet inputs"
    - "analysis and design of secure massive mimo systems in the presence of hardware impairments"
    - "performance limits of massive mimo systems based on bayes optimal inference"
    - "secure massive mimo transmission with an active eavesdropper"
    - "large scale mimo relaying techniques for physical layer security af or df"
    - "securing massive mimo at the physical layer"
    - "what will 5g be"
    - "blind pilot decontamination"

Connected through hyperedge HE-5 (induced by source paper "pilot spoofing attack by multiple eavesdroppers"):
  with members:
    - "admm based fast algorithm for multi group multicast beamforming in large scale wireless systems"
    - "impact of artificial noise on cellular networks a stochastic geometry approach"
    - "an algorithm for global maximization of secrecy rates in gaussian mimo wiretap channels"
    - "secure massive mimo transmission with an active eavesdropper"
    - "physical layer security in massive mimo"
    - "securing massive mimo at the physical layer"
    - "secure communication over parallel relay channel"
    - "robust secure transmission in miso channels based on worst case optimization"

Connected through hyperedge HE-6 (induced by source paper "analysis and design of secure massive mimo systems in the presence of hardware impairments"):
  with members:
    - "secure massive mimo systems with limited rf chains"
    - "physical layer security for massive mimo systems impaired by phase noise"
    - "linear precoding of data and artificial noise in secure massive mimo systems"
    - "energy efficient power control a look at 5g wireless technologies"
    - "hardware impairments aware transceiver for full duplex massive mimo relaying"
    - "per antenna constant envelope precoding for secure transmission in large scale miso systems"
    - "secure massive mimo transmission with an active eavesdropper"
    - "large scale mimo relaying techniques for physical layer security af or df"

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)