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: "theoretical bitcoin attacks with less than half of the computational power draft"
  Abstract: A widespread security claim of the Bitcoin system, presented in the original Bitcoin white-paper, states that the security of the system is guaranteed as long as there is no attacker in possession of half or more of the total computational power used to maintain the system. This claim, however, is proved based on theoretically flawed assumptions. #R##N#In the paper we analyze two kinds of attacks based on two theoretical flaws: the Block Discarding Attack and the Difficulty Raising Attack. We argue that the current theoretical limit of attacker's fraction of total computational power essential for the security of the system is in a sense not $\frac{1}{2}$ but a bit less than $\frac{1}{4}$, and outline proposals for protocol change that can raise this limit to be as close to $\frac{1}{2}$ as we want. #R##N#The basic idea of the Block Discarding Attack has been noted as early as 2010, and lately was independently though-of and analyzed by both author of this paper and authors of a most recently pre-print published paper. We thus focus on the major differences of our analysis, and try to explain the unfortunate surprising coincidence. To the best of our knowledge, the second attack is presented here for the first time.

Connected through hyperedge HE-1 (induced by source paper "exploring the attack surface of blockchain a systematic overview"):
  with members:
    - "scalable byzantine consensus via hardware assisted secret sharing"
    - "security services using blockchains a state of the art survey"
    - "a survey on the security of blockchain systems"
    - "an empirical analysis of anonymity in zcash"
    - "towards blockchain driven secure and transparent audit logs"
    - "end to end analysis of in browser cryptojacking"
    - "linbft linear communication byzantine fault tolerance for public blockchains"
    - "a survey on security and privacy issues of bitcoin"

Connected through hyperedge HE-2 (induced by source paper "a survey on applications of game theory in blockchain"):
  with members:
    - "a survey on consensus mechanisms and mining strategy management in blockchain networks"
    - "security services using blockchains a state of the art survey"
    - "blockchain governance game"
    - "exchange of renewable energy among prosumers using blockchain with dynamic pricing"
    - "game of coins"
    - "delayed blockchain protocols"
    - "reward sharing schemes for stake pools"
    - "a survey on the security of blockchain systems"

Connected through hyperedge HE-3 (induced by source paper "squirrl automating attack discovery on blockchain incentive mechanisms with deep reinforcement learning"):
  with members:
    - "competing semi selfish miners in bitcoin"
    - "sok transparent dishonesty front running attacks on blockchain"
    - "selfish mining in ethereum"
    - "mind the mining"
    - "flash boys 2 0 frontrunning transaction reordering and consensus instability in decentralized exchanges"
    - "selfish mining in ethereum"
    - "a deep dive into blockchain selfish mining"
    - "an introduction to deep reinforcement learning"

Connected through hyperedge HE-4 (induced by source paper "strongchain transparent and collaborative proof of work consensus"):
  with members:
    - "decentralization in bitcoin and ethereum networks"
    - "short paper towards more reliable bitcoin timestamps"
    - "the impact of uncle rewards on selfish mining in ethereum"
    - "the gap game"
    - "enhancing bitcoin security and performance with strong consistency via collective signing"
    - "optimal selfish mining strategies in bitcoin"
    - "bitcoin ng a scalable blockchain protocol"
    - "on subversive miner strategies and block withholding attack in bitcoin digital currency"

Connected through hyperedge HE-5 (induced by source paper "blockchain technologies for the internet of things research issues and challenges"):
  with members:
    - "a survey on the security of blockchain systems"
    - "a delay tolerant payment scheme based on the ethereum blockchain"
    - "towards trusted social networks with blockchain technology"
    - "a survey on security and privacy issues of bitcoin"
    - "an empirical analysis of linkability in the monero blockchain"
    - "blockchain a distributed solution to automotive security and privacy"
    - "teechain a secure asynchronous blockchain payment network"
    - "from pretty good to great enhancing pgp using bitcoin and the blockchain"

Connected through hyperedge HE-6 (induced by source paper "selfish mining in ethereum"):
  with members:
    - "deconstructing the blockchain to approach physical limits"
    - "zeroblock preventing selfish mining in bitcoin"
    - "optimal selfish mining strategies in bitcoin"
    - "majority is not enough bitcoin mining is vulnerable"

Connected through hyperedge HE-7 (induced by source paper "a survey on security and privacy issues of bitcoin"):
  with members:
    - "concurrency and privacy with payment channel networks"
    - "dandelion redesigning the bitcoin network for anonymity"
    - "consensus in the age of blockchains"
    - "when the cookie meets the blockchain privacy risks of web payments via cryptocurrencies"
    - "be selfish and avoid dilemmas fork after withholding faw attacks on bitcoin"
    - "socially optimal mining pools"
    - "the balance attack against proof of work blockchains the r3 testbed as an example"
    - "hijacking bitcoin routing attacks on cryptocurrencies"

Connected through hyperedge HE-8 (induced by source paper "research on the security of blockchain data a survey"):
  with members:
    - "enhancing bitcoin security and performance with strong consistency via collective signing"
    - "a blind mixing scheme for bitcoin based on an elliptic curve cryptography blind digital signature algorithm"
    - "centrally banked cryptocurrencies"
    - "deanonymisation of clients in bitcoin p2p network"
    - "bitcoin over tor isn t a good idea"
    - "on subversive miner strategies and block withholding attack in bitcoin digital currency"
    - "the miner s dilemma"
    - "majority is not enough bitcoin mining is vulnerable"

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)