human: Given a node-centered hypergraph: <hypergraph>, where nodes represent authors and hyperedges represent groups of authors who co-authored the same paper.

Details of the hypergraph:
Center node: "Achieving fine-grained access control for secure data sharing on cloud servers"
  Abstract: With more and more enterprises sharing their sensitive data on cloud servers, building a secure cloud environment for data sharing has attracted a lot of attention in both the industry and academic communities. In this paper, we propose a conjunctive precise and fuzzy identity-based encryption (PFIBE) scheme for secure data sharing on cloud servers, which allows the encryption of data by specifying a recipient identity (ID) set or a disjunctive normal form (DNF) access control policy over attributes, so that only the user whose ID belongs to the ID set or attributes satisfy the DNF access control policy can decrypt the corresponding data. Our design goal is to propose a novel encryption scheme, which simultaneously achieves a fine-grained access control, flexibility, high performance, and full key delegation, so as to help enterprise users to enjoy more secure, comprehensive, and flexible services. We achieve this goal by first combining the hierarchical identity-based encryption (HIBE) system and the ciphertext-policy attribute-based encryption (CP-ABE) system, and then marking each user with both an ID and a set of descriptive attributes, finally separating the access control policy into two parts: a recipient ID set and a DNF attribute-based access control policy. Copyright © 2011 John Wiley & Sons, Ltd.

Connected through hyperedge HE-1 (induced by source paper "Building access control policy model for privacy preserving and testing policy conflicting problems"):
  with members:
    - "Preserving Data Privacy and Security in Australian My Health Record System: A Quality Health Care Implication"

Connected through hyperedge HE-2 (induced by source paper "Collusion resistant broadcast encryption with short ciphertexts and private keys"):
  with members:
    - "Dual System Encryption: Realizing Fully Secure IBE and HIBE under Simple Assumptions"
    - "Public key encryption with conjunctive keyword search and its extension to a multi-user system"
    - "Plutus: Scalable Secure File Sharing on Untrusted Storage"
    - "Conjunctive Broadcast and Attribute-Based Encryption"
    - "Conditional Proxy Broadcast Re-Encryption"
    - "Pairing-Based cryptography at high security levels"
    - "Low Overhead Broadcast Encryption from Multilinear Maps"
    - "Graph-Induced Multilinear Maps from Lattices"

Connected through hyperedge HE-3 (induced by source paper "Dual System Encryption: Realizing Fully Secure IBE and HIBE under Simple Assumptions"):
  with members:
    - "Collusion resistant broadcast encryption with short ciphertexts and private keys"
    - "Functional encryption for inner product predicates from learning with errors"
    - "Fully secure functional encryption with general relations from the decisional linear assumption"
    - "New chosen-ciphertext secure identity-based encryption with tight security reduction to the bilinear Diffie-Hellman problem"

Question: Please tell me which research area the center author belongs to. The 4 classes are: Computer science, Mathematics, Engineering, Economics, Psychology, Business. Directly output the class name.

gpt: Computer science