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With the rapid development of cloud computing, a large number of web services have been emerging quickly, which brings a heavy burden for users to choose the services they preferred. In order to suggest web services for users, recommendation algorithms are needed and many of them have been investigated recently. However, most of the existing recommendation schemes are based on centralized historical data, which may lead to single point of failure. Generally, the data contains a lot of sensitive information that cloud may expose the privacy of users, which makes most cloud platforms reluctant to share their own data. In order to solve the above issues, the secure data sharing among cloud platforms is necessary for better recommendation, which can maximize the profits. In this paper, we propose a blockchain-assisted collaborative service recommendation scheme ( $BC - SRDS$ ). Specifically, we adopt the ciphertext-policy attribute-based encryption (CP-ABE) algorithm to encrypt the data, which ensures the data confidentiality and realizes secure data sharing. Then, we utilize the blockchain to share data, such that the DoS attack, DDoS attack and single point of failure can be avoided. Meanwhile, the data integrity, tampering-proof of data are guaranteed through the blockchain. And we use locality-sensitive hashing algorithm to recommend the services for users. Finally, it is proved through the security analysis that $BC - SRDS$ is capable of achieving data confidentiality, data integrity and tampering-proof. A series of experiments show that $BC - SRDS$ achieves better recommendation accuracy compared with the existing schemes.

Securing information dissemination is extremely important for various vehicular ad hoc networks (VANETs) applications. However, most of the applications require disseminating the critical information only to the authorized vehicles through V2I (Vehicle to Infrastructure) communications. Moreover, V2I communications usually suffer from incomplete information to vehicles in one RSU’s transmission range. Therefore, it is an even challenging task that how to ensure reliable dissemination of encrypted data to the recipient vehicles in multi-RSU settings. We propose a security-aware information dissemination scheme with fine-grained access control in cooperative multi-RSU of VANETs. Our proposed scheme uses ciphertext-policy attribute-based encryption (CP-ABE) to ensure confidential communication in a broadcasting way, which ensures that only the vehicles that satisfy the access control policy can have the ability to access the information; and we employ proxy re-encryption in the communication protocol to make sure the moving vehicles in high-speed can get the whole encrypted information. Performance analysis shows that our scheme can enable fine-grained access control for the broadcasted information, and make sure the vehicles receive reliable information in the whole disseminating process. And our scheme is applicable and efficient in various scenarios of information dissemination, especially in cooperative multi-RSU of VANETs. [ABSTRACT FROM AUTHOR]

In this article, we propose a revocable lattice-based CP-ABE (Ciphertext-Policy Attribute-Based Encryption) scheme (RL-ABE), which is suitable to be applied in the cloud storage. The RL-ABE scheme can resist quantum algorithm attack and ensure fine-grained access control to the users’ rights in achieving shared data. In addition, our scheme can realize attribute revocation, which can expediently renew users’ attributes to grant or revoke their access rights. Then, we formally prove the security of our scheme based on the hardness of Ring Learning with Error problem(R-LWE) to resist quantum algorithm attack, and prove our scheme can solve security threatens to withstand collusion attacks. Finally, the performance analysis shows the high efficiency of our scheme compared with other related schemes. [ABSTRACT FROM AUTHOR]

Cloud-assisted smart grid has been broadly deployed to improve the economics, efficiency, sustainability, and reliability of electricity services. The new revolution of technology will also bring new challenges to data security, particularly data confidentiality. As a promising encryption method for supporting fine-grained access control, attribute-based encryption (ABE) is widely given attention by the academia and industry. However, most existing schemes suffer from the efficiency problem limiting its deployment for the cloud-assisted smart grid, especially for resource-limited users. To address this problem, this paper proposes two efficient pairing-free ciphertext-policy attribute-based schemes that eliminate the computation-intensive bilinear pairing operation. The basic scheme only uses some simple scalar multiplications based on elliptic curves, and the enhanced scheme provides an important usability feature, namely the users and attributes revocation. The security of the proposed schemes is reduced to the elliptic curve decisional Diffie-Hellman problem. Finally, the performance analysis and extensive experiments demonstrate that our proposed schemes are suitable for the cloud-assisted smart grid.

In a ciphertext-policy attribute-based encryption (CP-ABE) system, the decryption keys are only related to attributes shared by multiple users and do not contain any identity information of their original holders. Hence, if a decryption key is leaked, there is no feasible method to trace the suspicious user. The user tracing problem has become an obstacle to the adoption of CP-ABE in practice. In order to address it, some traceable/accountable CP-ABE schemes have been established. However, considering the user tracing problem in multi-domain environment will face new challenges. Multi-domain environments usually have a two-layer structure, domains and intradomain users. When tracing a user, we should first trace the domain where the user is located, and then trace the user in the domain. Unfortunately, the existing traceable CP-ABE schemes only focus on one level of users tracing, and are not suitable for the two-layer structure of multi-domain environments. Therefore, a white-box traceable CP-ABE scheme in multi-domain environment is proposed in this paper. The proposed scheme obtains a so-called two-layer tracing. At the domain level, a short signature technique is used to prevent an attacker from forging the tracing parameter and realize the traceability for domains. Linkable ring signature technology is introduced at the user level to provide a tracing method for users by utilizing the linkability of the signature. The two signature structures are reasonably embedded in a user private key to support two-layer white-box tracing at both domains and intradomain users. The proposed scheme supports any monotone access structures and has full security against chosen plaintext attack in the standard model. Compared with related schemes, the asymptotic communication cost and the asymptotic computation cost of the proposed scheme are relatively low. These advantages make the proposed scheme more practical for solving the user tracing problem in multi-domain environment.

Searchable encryption (SE) has been a promising technology which allows users to perform search queries over encrypted data. However, the most of existing SE schemes cannot deal with the shared records that have hierarchical structures. In this paper, we devise a basic cryptographic primitive called as attribute-based keyword search over hierarchical data (ABKS-HD) scheme by using the ciphertext-policy attribute-based encryption (CP-ABE) technique, but this basic scheme cannot satisfy all the desirable requirements of cloud systems. The facts that the single keyword search will yield many irrelevant search results and the revoked users can access the unauthorized data with the old or outdated secret keys make this basic scheme not scale well in practice. To this end, we also propose two improved schemes (ABKS-HD-I, ABKS-HD-II) for the sake of supporting multi-keyword search and user revocation, respectively. In contrast with the state-of-the-art attribute-based keyword search (ABKS) schemes, the computation overhead of our schemes almost linearly increases with the number of users’ attributes rather than the number of attributes in systems. Formal security analysis proves that our schemes are secure against both chosen-plaintext attack (CPA) and chosen-keyword attack (CKA) in the random oracle model. Furthermore, empirical study using a real-world dataset shows that our schemes are feasible and efficient in practical applications. [ABSTRACT FROM AUTHOR]

ABKS has drawn much attention from research and industry in recent years, an ABKS scheme is an encryption scheme that supports keyword search and access control. Attribute-Based Encryption is a public key encryption that enables users to encrypt and decrypt message based on attributes. In a typical implementation, the size of the ciphertext is proportional to the number of attributes associated with it and the decryption time is proportional to the number of attributes used during decryption. Inherit from ABE technology, the computation cost and ciphertext size in most ABKS schemes grow with the complexity of the access policy. On the other hand, we found that the traditional ABKS schemes cannot resist our secret-key-recovery attack. To deal with the above problems, we present new ciphertext policy attribute based encryption with fast keyword search constructions. Our constructions preserve the fine-grained access control inherited from the ABE system while supporting hidden policy and fast keyword search. Our constructions feature multi-value-independent compared with the existing attribute based searchable encryption schemes. The performance analysis demonstrates the efficiency of our constructions. We offer rigorous security proof of our second scheme, which is IND-CKA and IND-CPA secure. [ABSTRACT FROM AUTHOR]

The rapid development of smart wearable devices makes personal health management feasible, which also stimulates the evolution of personal health records (PHRs). However, PHRs face many security challenges ever since it has been created. Besides, the complicated policy adjusting operation makes the PHRs stored in the cloud not so easy to use. In this paper, we propose a lightweight PHRs system on the basis of attribute-based encryption with policy updating. To update an outsourced ciphertext PHRs in the cloud, PHRs owners only need to generate an updating key, then upload it to the cloud server instead of retrieving the entire ciphertexts. We proved the security of our scheme, and the experiment result indicates that our system is much more efficient than the brute force way of ciphertext updating.

Ciphertext-policy attribute-based encryption (CP-ABE) is widely used in many cyber physical systems and the Internet of Things for guaranteeing information security. In order to improve the performance and efficiency of CP-ABE, this paper makes a change to the access structure of describing access polices in CP-ABE, and presents a new CP-ABE system based on the ordered binary decision diagram (OBDD). The new system makes full use of both the powerful description ability and the high calculating efficiency of OBDD. First, in the access structure, the new system allows multiple occurrences of the same attribute in a strategy, supports both positive attribute and negative attribute in the description of access polices, and can describe free-form access polices by using Boolean operations. Second, in the key generation stage, the size of secret keys generated by the new system is constant and not affected by the number of attributes; furthermore, time complexity of the key generation algorithm is O(1). Third, in the encryption stage, both the time complexity of the encryption algorithm and the size of generated ciphertext are determined by the number of valid paths contained in the OBDD instead of the number of attributes occurring in access polices. Finally, in the decryption stage, the new system supports fast decryption and the time complexity of the decryption algorithm is only O(1). As a result, compared with existing CP-ABE schemes, the new system has better performance and efficiency. It is proved that the new CP-ABE system can also resist collision attack and chosen-plaintext attack under the decisional bilinear Diffie Hellman assumption.

Designing lightweight security protocols for cloud-based Internet-of-Things (IoT) applications for battery-limited mobile devices, such as smart phones and laptops, is a topic of recent focus. Ciphertextpolicy attribute-based encryption (CP-ABE) is a viable solution, particularly for cloud deployment, as an encryptor can “write”the access policy so that only authorized users can decrypt and have access to the data. However, most existing CP-ABE schemes are based on the costly bilinear maps, and require long decryption keys, ciphertexts and incur significant computation costs in the encryption and decryption (e.g. costs is at least linear to the number of attributes involved in the access policy). These design drawbacks prevent the deployment of CP-ABE schemes on battery-limited mobile devices. In this paper, we propose a new RSA-based CP-ABE scheme with constant size secret keys and ciphertexts (CSKC) and has O(1) time-complexity for each decryption and encryption. Our scheme is then shown to be secure against a chosen-ciphertext adversary, as well as been an efficient solution with the expressive AND gate access structures (in comparison to other related existing schemes). Thus, the proposed scheme is suitable for deployment on battery-limited mobile devices.

For enterprise systems running on public clouds in which the servers are outside the control domain of the enterprise, access control that was traditionally executed by reference monitors deployed on the system servers can no longer be trusted. Hence, a self-contained security scheme is regarded as an effective way for protecting outsourced data. However, building such a scheme that can implement the access control policy of the enterprise has become an important challenge. In this paper, we propose a self-contained data protection mechanism called RBAC-CPABE by integrating role-based access control (RBAC), which is widely employed in enterprise systems, with the ciphertext-policy attribute-based encryption (CP-ABE). First, we present a data-centric RBAC (DC-RBAC) model that supports the specification of fine-grained access policy for each data object to enhance RBAC's access control capabilities. Then, we fuse DC-RBAC and CP-ABE by expressing DC-RBAC policies with the CP-ABE access tree and encrypt data using CP-ABE. Because CP-ABE enforces both access control and decryption, access authorization can be achieved by the data itself. A security analysis and experimental results indicate that RBAC-CPABE maintains the security and efficiency properties of the CP-ABE scheme on which it is based, but substantially improves the access control capability. Finally, we present an implemented framework for RBAC-CPABE to protect privacy and enforce access control for data stored in the cloud.

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. [ABSTRACT FROM AUTHOR]