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: "airtnt fair exchange payment for outsourced secure enclave computations"
  Abstract: We present Airtnt, a novel scheme that enables users with CPUs that support Trusted Execution Environments (TEEs) and remote attestation to rent out computing time on secure enclaves to untrusted users. Airtnt makes use of the attestation capabilities of TEEs and smart contracts on distributed ledgers to guarantee the fair exchange of the payment and the result of an execution. Airtnt makes use of off-chain payment channels to allow requesters to pay executing nodes for intermediate "snapshots" of the state of an execution. Effectively, this step-by-step "compute-payment" cycle realises untrusted pay-as-you-go micropayments for computation. Neither the requester nor the executing node can walk away and incur monetary loss to the other party. This also allows requesters to continue executions on other executing nodes if the original executing node becomes unavailable or goes offline.

Connected through hyperedge HE-1 (induced by source paper "trustee full privacy preserving vickrey auction on top of ethereum"):
  with members:
    - "ekiden a platform for confidentiality preserving trustworthy and performant smart contracts"
    - "blockchain and trusted computing problems pitfalls and a solution for hyperledger fabric"
    - "malware guard extension using sgx to conceal cache attacks"
    - "inferring fine grained control flow inside sgx enclaves with branch shadowing"
    - "teechan payment channels using trusted execution environments"
    - "proof of luck an efficient blockchain consensus protocol"
    - "ipfs content addressed versioned p2p file system"

Connected through hyperedge HE-2 (induced by source paper "asterisk auction based shared economy resolution system for blockchain"):
  with members:
    - "spoc secure payments for outsourced computations"
    - "coconut threshold issuance selective disclosure credentials with applications to distributed ledgers"
    - "chainspace a sharded smart contracts platform"

Connected through hyperedge HE-3 (induced by source paper "proof of prestige a useful work reward system for unverifiable tasks"):
  with members:
    - "spoc secure payments for outsourced computations"
    - "consensus in the age of blockchains"
    - "casper the friendly finality gadget"

Connected through hyperedge HE-4 (induced by source paper "fair marketplace for secure outsourced computations"):
  with members:
    - "instantaneous decentralized poker"
    - "powers of tensors and fast matrix multiplication"

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)