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: "decentralized trusted timestamping using the crypto currency bitcoin"
  Abstract: Trusted timestamping is a process for proving that certain information existed at a given point in time. This paper presents a trusted timestamping concept and its implementation in form of a web-based service that uses the decentralized Bitcoin block chain to store anonymous, tamper-proof timestamps for digital content. The service allows users to hash files, such as text, photos or videos, and store the created hashes in the Bitcoin block chain. Users can then retrieve and verify the timestamps that have been committed to the block chain. The non-commercial service enables anyone, e.g., researchers, authors, journalists, students, or artists, to prove that they were in possession of certain information at a given point in time. Common use cases include proving that a contract has been signed, a photo taken, a video recorded, or a task completed prior to a certain date. All procedures maintain complete privacy of the user’s data.

Connected through hyperedge HE-1 (induced by source paper "the security reference architecture for blockchains towards a standardized model for studying vulnerabilities threats and defenses"):
  with members:
    - "ekiden a platform for confidentiality preserving trustworthy and performant smart contracts"
    - "a survey on ethereum systems security vulnerabilities attacks and defenses"
    - "security and privacy on blockchain"
    - "deconstructing blockchains a comprehensive survey on consensus membership and structure"
    - "truffle tests for free replaying ethereum smart contracts for transparency"
    - "blockchain technologies for the internet of things research issues and challenges"
    - "exploring the attack surface of blockchain a systematic overview"
    - "strongchain transparent and collaborative proof of work consensus"

Connected through hyperedge HE-2 (induced by source paper "properties of decentralized consensus technology why not every blockchain is a blockchain"):
  with members:
    - "decentralization in bitcoin and ethereum networks"
    - "blockchain technology overview"
    - "sharvot secret share based voting on the blockchain"
    - "stampery blockchain timestamping architecture bta version 6"
    - "casper the friendly finality gadget"
    - "bitcoin ng a scalable blockchain protocol"
    - "cryptocurrencies without proof of work"
    - "majority is not enough bitcoin mining is vulnerable"

Connected through hyperedge HE-3 (induced by source paper "archive assisted archival fixity verification framework"):
  with members:
    - "mementomap framework for flexible and adaptive web archive profiling"
    - "difficulties of timestamping archived web pages"
    - "making digital artifacts on the web verifiable and reliable"
    - "trusty uris verifiable immutable and permanent digital artifacts for linked data"
    - "http mailbox asynchronous restful communication"
    - "memento time travel for the web"
    - "preserving peer replicas by rate limited sampled voting"

Connected through hyperedge HE-4 (induced by source paper "redactable blockchain in the permissionless setting"):
  with members:
    - "rollerchain a blockchain with safely pruneable full blocks"
    - "modeling bitcoin contracts by timed automata"
    - "majority is not enough bitcoin mining is vulnerable"

Connected through hyperedge HE-5 (induced by source paper "a decentralized method for making sensor measurements tamper proof to support open science applications"):
  with members:
    - "using block chain for peer to peer proof of location"

Connected through hyperedge HE-6 (induced by source paper "a web of blocks"):
  with members:
    - "scalable byzantine consensus via hardware assisted secret sharing"
    - "enhancing accountability and trust in distributed ledgers"

Connected through hyperedge HE-7 (induced by source paper "difficulties of timestamping archived web pages"):
  with members:
    - "impact of uri canonicalization on memento count"
    - "rules of acquisition for mementos and their content"
    - "a framework for evaluation of composite memento temporal coherence"
    - "an evaluation of caching policies for memento timemaps"
    - "memento time travel for the web"
    - "transparent format migration of preserved web content"

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)