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Analysis of Lightweight Attribute-Based Encryption Schemes and Presentation of Two New Schemes

Abdollahi, Sina | 2022

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 55143 (05)
  4. University: Sharif University of Technolog
  5. Department: Electrical Engineering
  6. Advisor(s): Mohajeri, Javad; Salmasizadeh, Mahmoud
  7. Abstract:
  8. Cloud storage provides an accessible and cheap space for data storage. There is usually no trust between users and the Cloud. Consequently, to maintain confidentiality, outsourcing and storing sensitive data in an encrypted form is necessary. In applications where data sharing between several users is required, ciphertext-policy attribute-based encryption(CP-ABE) has been considered a promising solution, but the lack of efficiency and flexibility limits its usage in applications such as IoT. These problems are usually related to both the underlying structure and the required peripheral processes, such as key revocation. In this thesis, two schemes with the same basic structure and different revocation methods are proposed. The proposed schemes use linear secret sharing to implement access structure. Furthermore, in the decryption process, only a fixed number of pairings is used, which is independent of the number of attributes used in the decryption process. In addition, the decryption can be outsourced. It is shown that the above properties lead to high efficiency and flexibility in the proposed schemes. Both schemes are selectively secure in the standard model. In this thesis, in addition to the performance improvement on the user side, which is the main issue in most studies, the performance improvement of the trusted authority is considered. In both proposed schemes, the user-side computational burden is similar, but their main difference is related to the computational burden on the trusted authority side. The trusted authority is in contact with all users and is responsible for users' key generation and revocation. Therefore, in addition to the scheme properties, each user behavior affects the computational burden of the trusted authority. Consequently, unlike the computational burden on the user side, analysis of the trusted authority's computational burden is not straightforward. By defining a model of the system in a real situation, it will be possible to analyze the computational burden of the trusted authority. This model has been applied to various schemes as well as the proposed schemes and the relationship of the trusted authority's computational burden with the number of users N and their average behavior, which is defined by several parameters, is obtained. we have shown that the computational burden of the trusted authority is at the order O(N2) in the first proposed scheme and at the order O(N) in the second proposed scheme which are better than most previous reviewed schemes. Furthermore, with the increase in the number of users, the computational burden of the trusted authority in the second proposed scheme will be significantly less than the other reviewed schemes. In other words, the revocation method in the second proposed scheme is suitable for large-scale systems. Comparing the first and second schemes, according to the number of system users, an equality point Ne is found so that for N ≥ Ne, the computational burden of the trusted authority in the second proposed scheme will be less than the first proposed scheme. Thus, depending on the number of system users and their average behavior, a more appropriate scheme can be selected
  9. Keywords:
  10. Attribute Based Encryption ; Internet of Things ; Key Revocation ; Trusted Authority ; Pairings ; Trusted Authority's Computational Burden

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