Multi-Authority Attribute Based Keyword Search Over Encrypted Cloud Data

Searchable Encryption (SE) is an important technique to guarantee data security and usability in the cloud at the same time. Leveraging Ciphertext-Policy Attribute-Based Encryption (CP-ABE), the Ciphertext-Policy Attribute-Based Keyword Search (CP-ABKS) scheme can achieve keyword-based retrieval and fine-grained access control simultaneously. However, the single attribute authority in existing CP-ABKS schemes is tasked with costly user certificate verification and secret key distribution. In addition, this results in a single-point performance bottleneck in distributed cloud systems. Thus, in this paper, we present a secure Multi-authority CP-ABKS (MABKS) system to address such limitations and minimize the computation and storage burden on resource-limited devices in cloud systems. In addition, the MABKS system is extended to support malicious attribute authority tracing and attribute update. Our rigorous security analysis shows that the MABKS system is selectively secure in both selective-matrix and selective-attribute models. Our experimental results using real-world datasets demonstrate the efficiency and utility of the MABKS system in practical applications.

Searchable Encryption (SE) is a crucial technique for cloud data security and usability (SE). When employing Ciphertext Policy Attribute-Based Encryption (CP-ABE) and the Ciphertext Policy Attribute-Based Keyword Search (CP-ABKS), encryption and access control may be done simultaneously. A single attribute authority is responsible for authenticating user certificates and delivering secret keys in current CP-ABKS systems. A single point of failure results in distributed cloud systems. To address these difficulties, we explain in this paper the MABKS system, which is designed to help cloud devices with limited computing and storage capabilities. The MABKS system has added capability for tracing and modifying malicious attribute authority. According to our detailed security investigation, the MABKS system is safe in both selective-matrix and selective-attribute models. Our trials using real-world datasets have shown the MABKS system's efficiency and usefulness.

Data access control is a challenging issue in public cloud storage systems. Ciphertext-Policy Attribute-Based Encryption (CP-ABE) has been adopted as a promising technique to provide flexible, fine-grained and secure data access control for cloud storage with honest-but-curious cloud servers. However, in the existing CP-ABE schemes, the single attribute authority must execute the time-consuming user legitimacy verification and secret key distribution, and hence it results in a single-point performance bottleneck when a CP-ABE scheme is adopted in a large-scale cloud storage system. Users may be stuck in the waiting queue for a long period to obtain their secret keys, thereby resulting in low-efficiency of the system. Although multiauthority access control schemes have been proposed, these schemes still cannot overcome the drawbacks of single-point bottleneck and low efficiency, due to the fact that each of the authorities still independently manages a disjoint attribute set

Outsourcing data to some cloud servers enables a massive, flexible usage of cloud computing resources and it is typically held by different organizations and data owners. However, various security concerns have been raised due to hosting sensitive data on an untrusted cloud environment, and the control over such data by their owners is lost after uploading to the cloud. Access control is the first defensive line that forbids unauthorized access to the stored data. Moreover, fine-grained access control on the untrusted cloud can be enforced using advanced cryptographic mechanisms. Some schemes have been proposed to deliver such access control using Ciphertext-policy attribute based encryption (CP-ABE) that can enforce data owners’ access policies to achieve such cryptographic access control and tackle the majority of those concerns. However, some challenges are still outstanding due to the complexity of frequently changing the cryptographic enforcements of the owners’ access policies in the hosted cloud data files, which poses computational and communicational overheads to data owners. These challenges are: 1) making dynamic decisions to grant access rights to the cloud resources, 2) solving the issue of the revocation process that is considered as a performance killer, and 3) building a collusion resistant system. The aim of our work is to construct an access control scheme that provides secure storing and sharing sensitive data on the cloud and suits limited-resources devices. In this thesis, we analyse some of the existing, related issues and propose a scheme that extends the relevant existing techniques to resolve the inherent problems in CP-ABE without incurring heavy computation overhead. In particular, most existing revocation techniques require re-issuing many private keys for all non-revoked users as well as re-encrypting the related ciphertexts. Our proposed scheme offers a solution to perform a novel technique that dynamically changes the access privileges of legitimate users. The scheme drives the access privileges in a specific way by updating the access policy and activating a user revocation property. Our technique assigns processing-intensive tasks to cloud servers without any information leakage to reduce the computation cost on resource-limited computing devices. Our analytical theoretical and experimental findings and comparisons of our work with related existing systems indicate that our scheme is efficient, secure and more practical compared to the current related systems, particularly in terms of policy updating and ciphertext re-encryption. Therefore, our proposed scheme is suited to Internet of Things (IoT) applications that need a practical, secure access control scheme. Moreover, to achieve secure, public cloud storage and minimise the limitations of CP-ABE which mainly supports storing data only on a private cloud storage system managed by only one single authority, our proposed access control scheme is extended to a secure, critical access control scheme with multiple authorities. This scheme ought to be carefully designed to achieve fine-grained access control and support outsourced-data confidentiality. In addition, most existing multi-authority access control schemes do not properly consider the revocation issue due to the difficulty of addressing it in distributed settings. Therefore, building a multi-authority CP-ABE scheme along with addressing changes to policy attributes and users, have motivated many researchers to develop more suitable schemes with limited success. By leveraging the existing work, in this thesis, we propose a second CP-ABE scheme that tackles most of the existing work’s limitations and allows storing data securely on a public cloud storage system by employing multiple authorities which manage a joint set of attributes. Furthermore, the proposed scheme efficiently maintains the revocation by adapting the two techniques used in the first proposed single authority access control scheme to allow dynamic policy update and invalidate a revoked user’s secret key that eliminates collusion attacks. In terms of computation overhead, the proposed multi-authority scheme outsources expensive operations of encryption and decryption to a cloud server to mitigate the burden on a data owner and data users, respectively. Our scheme analysis and the theoretical and implemented results demonstrate that our scheme is scalable and efficient.

The pervasive, ubiquitous, and heterogeneous properties of IoT make securing IoT systems a very challenging task. More so when access and storage are performed through a cloud-based IoT system. IoT data stored on cloud should be encrypted to ensure data privacy. It is also crucial to allow only authorized entities to access and decrypt the encrypted data. In this article, we propose a ciphertext-policy attribute-based encryption (CP-ABE) scheme that enables fine-grained access control of encrypted IoT data on cloud. CP-ABE is regarded as a highly promising approach to provide flexible and fine-grained access control, which is quite suited to secure cloud based IoT systems. We first present an access control system model of CloudIoT platform based on ABE. Based on the presented system model, we construct a ciphertext-policy hiding CP-ABE scheme, which guarantees the privacy of the users. We further construct a white-box traceable CP-ABE scheme with accountability in order to address the user key abuse and authorization center key abuse. Experiment illustrates the proposed systems are efficient.

Attribute-based encryption (ABE) can propose the fine-grained access control policy for encrypted data in cloud. The characteristics of the attributes in the existing works are treated as same level but in the real life the attributes and domain authorities are always in the different levels. It produces additional computation costs and storage costs for users. To overcome these shortcomings, a new ABE scheme is proposed in this paper. The proposed scheme combines the ciphertext-policy attribute-based encryption (CP-ABE) scheme with hierarchical identity-based encryption (HIBE) which issues a ciphertext-policy hierarchical attribute-based encryption (CP-HABE). Both the main domain authorisations and users achieve hierarchical encryption under the fine-grained access control. In addition, the proposed scheme inherits flexibility and achieves scalability with short ciphertexts. Under three static assumptions instead of other strong assumptions, it also achieves full security in the standard model.

In the area of searchable encryption, public key encryption with keyword search (PEKS) has been a critically important and promising technique which provides secure search over encrypted data in cloud computing. PEKS can protect user data privacy without affecting the usage of the data stored in the untrusted cloud server environment. However, most of the existing PEKS schemes concentrate on data users’ rich search functionalities, regardless of their search permission. Attribute-based encryption technology is a good method to solve the security issues, which provides fine-grained access control to the encrypted data. In this paper, we propose a privacy-preserving and efficient public key encryption with keyword search scheme by using the ciphertext-policy attribute-based encryption (CP-ABE) technique to support both fine-grained access control and keyword search over encrypted data simultaneously. We formalize the security definition, and prove that our scheme achieves selective indistinguishability security against an adaptive chosen keyword attack. Finally, we present the performance analysis in terms of theoretical analysis and experimental analysis, and demonstrate the efficiency of our scheme.

Searchable Encryption(SE) schemes allow users to perform keyword search on encrypted data without leakage of the sensitive information. Most of the existing SE schemes are limited to single-user setting or multi-user setting with coarser-grained access control. However, the application that multiple users with different access rights to the sharing data is more practical under the cloud environment. To bridge this gap, we consider searchable encryption with fine-grained access control under multi-user setting in this paper. The proposed scheme requires less computation cost at user side but provides fine-grained access control to authorized users under a new hybrid architecture. Combining symmetric encryption and Cipher text-Policy Attribute based Encryption(CP-ABE), we achieve a user collusion resistant scheme with the help of the private cloud. Our scheme solves a prevalent problem of key sharing. And the exposure of attribute secret key to the public cloud will not affect the system security. Dynamic and efficient user revocation is also provided. Security analysis shows that our scheme is secure.

In the cloud, for achieving access control and keeping data confidential, the data owners could adopt attribute-based encryption to encrypt the stored data. Users with limited computing power are however more likely to delegate the mask of the decryption task to the cloud servers to reduce the computing cost. As a result, attribute-based encryption with delegation emerges. Still, there are caveats and questions remaining in the previous relevant works. For instance, during the delegation, the cloud servers could tamper or replace the delegated ciphertext and respond a forged computing result with malicious intent. They may also cheat the eligible users by responding them that they are ineligible for the purpose of cost saving. Furthermore, during the encryption, the access policies may not be flexible enough as well. Since policy for general circuits enables to achieve the strongest form of access control, a construction for realizing circuit ciphertext-policy attribute-based hybrid encryption with verifiable delegation has been considered in our work. In such a system, combined with verifiable computation and encrypt-then-mac mechanism, the data confidentiality, the fine-grained access control and the correctness of the delegated computing results are well guaranteed at the same time. Besides, our scheme achieves security against chosen-plaintext attacks under the k-multilinear Decisional Diffie-Hellman assumption. Moreover, an extensive simulation campaign confirms the feasibility and efficiency of the proposed solution. Index Terms—Ciphertext-policy attribute-based encryption, Circuits, Verifiable delegation, Multilinear map, Hybrid encryption. F

In the cloud, for achieving access control and keeping data confidential, the data owners could adopt attribute-based encryption to encrypt the stored data. Users with limited computing power are however more likely to delegate the mask of the decryption task to the cloud servers to reduce the computing cost. As a result, attribute-based encryption with delegation emerges. Still, there are caveats and questions remaining in the previous relevant works. For instance, during the delegation, the cloud servers could tamper or replace the delegated ciphertext and respond a forged computing result with malicious intent. They may also cheat the eligible users by responding them that they are ineligible for the purpose of cost saving. Furthermore, during the encryption, the access policies may not be flexible enough as well. Since policy for general circuits enables to achieve the strongest form of access control, a construction for realizing circuit ciphertext-policy attribute-based hybrid encryption with verifiable delegation has been considered in our work. In such a system, combined with verifiable computation and encrypt-then-mac mechanism, the data confidentiality, the fine-grained access control and the correctness of the delegated computing results are well guaranteed at the same time. Besides, our scheme achieves security against chosen-plaintext attacks under the $k$ -multilinear Decisional Diffie-Hellman assumption. Moreover, an extensive simulation campaign confirms the feasibility and efficiency of the proposed solution.

The development of cloud computing has brought a lot of advantages, such as reducing the hardware cost and a more convenient storage solution. Because of the convenient and cheap storage solution, a large number of users put their valuable data onto the cloud. There have been more and more outsourcing data security and privacy issues. Several schemes using attribute-based encryption (ABE) have been proposed in cloud computing outsourcing data access control, However, most of them have stubborn in complex access control policy. To implement scalable, flexible and fine-grained access control in cloud storage, this paper proposes an attribute-based solution with time restriction delegate by extending the Ciphertext-policy attribute-based encryption (CP-ABE). This scheme not only realizes the scalability and fine-grained access control, but also gives a solution for the data delegate. Our delegate mechanism can let the users entrusted the data which in their visit range to others, and the ability to set a time limit. Finally, we prove the security of our scheme based on the security of the Ciphertext-policy attribute-based encryption (CP-ABE) by Bethencourt et al. and analyze its performance and computational complexity. Experiments for our scheme are implemented and the result shows that it is both efficient and flexible in dealing with access control for outsourced data in cloud computing.

With the popular application of cloud storage and the diversification of terminal devices, especially the widespread popularization of smart terminals. Users have more and more requirements for how to access information in the cloud safely and efficiently. Ciphertext policy attribute-based encryption (CP-ABE) is an effective method to achieve fine-grained access control of cloud data. However, the large decryption overhead is a potential problem of attribute-based encryption. In this paper, a CP-ABE access control scheme based on proxy re-encryption is proposed, it helps markedly reduce the user’s decryption overhead. Meanwhile, attribute revocation is provided for key update while ensuring fine-grained access control, and an improved decryption key generation method is proposed, which solves the data leakage problem caused by illegal stealing private key in the traditional CP-ABE scheme. A comparison with other CP-ABE schemes shows that our scheme has better decryption performance for mobile devices accessing cloud data.

Cloud computing has revolutionized data storage and processing, but it has also introduced significant challenges in ensuring data privacy and access control. In this research paper, we explore and understand the potential of Ciphertext Policy Attribute-Based Encryption (CP-ABE) as a cryptographic solution for enhancing cloud security through fine-grained access control. Our exploration begins with a comprehensive analysis of CP-ABE, including its architecture, components, and encryption/decryption processes. We delve into the security aspects of CP-ABE, evaluating its strengths, advantages, and vulnerabilities. We conduct a thorough performance evaluation, analyzing its computational overhead and comparingits efficiency with other encryption techniques commonly used in the cloud. Our findings indicate that CP-ABE offers fine-grained access control and data confidentiality, empowering data owners to enforce complex access policies. However, challenges related to attribute authority trust, key escrow, and policy complexity must be addressed to ensure its robustness in real-world deployments.Ciphertext Policy Attribute-Based Encryption (CP-ABE) introduces a hopeful method for dealing with the challenges related to controlling who can access information and keeping data private in cloud computing.Our research contributes valuable insights into CP-ABE's security, performance, and practical applications.

For realizing the flexible, scalable and fuzzy fine-grained access control, ciphertext policy attribute-based encryption (CP-ABE) scheme has been widely used in the cloud storage system. However, the access structure of CP-ABE scheme is outsourced to the cloud storage server, resulting in the disclosure of access policy privacy. In addition, there are multiple authorities that coexist and each authority is able to issue attributes independently in the cloud storage system. However, existing CP-ABE schemes cannot be directly applied to data access control for multi-authority cloud storage system, due to the inefficiency for user revocation. In this paper, to cope with these challenges, we propose a decentralized multi-authority CP-ABE access control scheme, which is more practical for supporting the user revocation. In addition, this scheme can protect the data privacy and the access policy privacy with policy hidden in the cloud storage system. Here, the access policy that is realized by employing the linear secret sharing scheme. Finally, the security and performance analyses demonstrate that our scheme has high security in terms of access policy privacy and efficiency in terms of computational cost of user revocation.

Lattice-based Attribute-based encryption is a well-known cryptographic mechanism that can resist quantum attacks and has the ability of fine-grained access control, and it has a wide range of application scenarios in current Internet of Thing (IoT) era. However, lack of efficiency and existing the problem of large ciphertext expansion rate are the main disadvantages impede the applications of this mechanism. Thus, we propose an efficient and practical ciphertext policy attribute-based encryption (CP-ABE) scheme from lattices in the paper. In this scheme, to make the secret key reusable, we adjust access tree and propose a basic access tree structure, which can be converted from disjunctive normal form, and combine it with a light post-quantum scheme of Kyber. In addition, the compression method and plaintext expansion method are introduced to optimize the scheme. Our CP-ABE scheme is secure against chosen plaintext attack under the hardness of module learning with errors problem. We implement our scheme and compare it with three recent related schemes in terms of security, function and communication cost. Experiments and comparisons show that our CP-ABE scheme has advantages in high encryption efficiency, small matrix dimension, small key sizes, and low ciphertext expansion rate, which has some merit in practice.