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: "pki safety net pkisn addressing the too big to be revoked problem of the tls ecosystem"
  Abstract: In a public-key infrastructure (PKI), clients must have an efficient and secure way to determine whether a certificate was revoked (by an entity considered as legitimate to do so), while preserving user privacy. A few certification authorities (CAs) are currently responsible for the issuance of the large majority of TLS certificates. These certificates are considered valid only if the certificate of the issuing CA is also valid. The certificates of these important CAs are effectively too big to be revoked, as revoking them would result in massive collateral damage. To solve this problem, we redesign the current revocation system with a novel approach that we call PKI Safety Net (PKISN), which uses publicly accessible logs to store certificates (in the spirit of Certificate Transparency) and revocations. The proposed system extends existing mechanisms, which enables simple deployment. Moreover, we present a complete implementation and evaluation of our scheme.

Connected through hyperedge HE-1 (induced by source paper "proxy certificates the missing link in the web s chain of trust"):
  with members:
    - "the rise of certificate transparency and its implications on the internet ecosystem"
    - "tracking users across the web via tls session resumption"
    - "ritm revocation in the middle"

Connected through hyperedge HE-2 (induced by source paper "blockpki an automated resilient and transparent public key infrastructure"):
  with members:
    - "securify practical security analysis of smart contracts"
    - "ritm revocation in the middle"
    - "keeping authorities honest or bust with decentralized witness cosigning"
    - "efficient gossip protocols for verifying the consistency of certificate logs"

Connected through hyperedge HE-3 (induced by source paper "blockchain based tls notary service"):
  with members:
    - "short paper towards more reliable bitcoin timestamps"
    - "keeping authorities honest or bust with decentralized witness cosigning"

Connected through hyperedge HE-4 (induced by source paper "key exchange with the help of a public ledger"):
  with members:
    - "application of public ledgers to revocation in distributed access control"

Connected through hyperedge HE-5 (induced by source paper "ritm revocation in the middle"):
  with members:
    - "efficient gossip protocols for verifying the consistency of certificate logs"

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)