Cloud storage has become the most attractive way to achieve data sharing by setting flexible access policies. Cryptographic tools are considered the most popular approach to protecting the privacy of data stored on the cloud. Dividing data into different classes plays a significant role in cloud storage, making data organization more methodical and data sharing more expressive and efficient. Unfortunately, current data sharing solutions either neglect data classification or suffer from data leakage. Specifically, shared keys can decrypt newly added encrypted data within the same class, and have key abuse issues where shared keys are untraceable once sold. In this work, we propose a time-bound data sharing system that addresses all these issues simultaneously. In our scheme, data is divided into different classes and encrypted according to its class and associated time period. Decryption keys for a set of chosen data classes can be aggregated into a single key, allowing users to decrypt multiple ciphertexts whose classes are within the set. While other encrypted data with classes outside the set remain confidential. Moreover, the aggregate key is time-bound which can only decrypt the ciphertexts generated before the embedded time period, ensuring it cannot access newly added encrypted data. The key size is independent of the chosen class set size and is only logarithmic in the bit length of the time period used. For each sharing, the shared aggregate key is different. In the event of data leakage or key selling, the data provider can identify the responsible users. We provide formal security analysis of our system and evaluate its performance through experiments. The results demonstrate that our system is highly efficient in terms of shared keys. It provides a practical solution for achieving efficient and dynamic data sharing in cloud storage.

In healthcare systems, the protection of the sensitive data of patient during sharing across multiple entities is crucial. Encrypting these data before outsourcing to the healthcare server is an effective method to protect data privacy. As a solution to protect data sharing within healthcare systems, identity-based encryption with equality test (IBEET) is an effective strategy that allows testing whether two ciphertexts encrypted from the same plaintext without certificate management. However, current IBEET schemes often lack of control over the trapdoors’ lifetime, i.e. the malicious server could use trapdoor to test whether two ciphertext generated after the trapdoor encrypted by the same plaintext all the time, potentially leaking sensitive data which the user are unwilling to see. To address this problem, we introduce a forward secure identity-based encryption with equality test (FS-IBEET) scheme. This new scheme prevents the malicious server from accessing useful information from newly encrypted files. We perform a thorough security analysis using the random oracle model under the q-BDHI assumption. Our experiments demonstrate that the performance of our scheme in comparison to other schemes.

In EMR systems, numerous electronic medical records are usually uploaded to cloud servers for storage and data sharing. Public key authenticated encryption with keyword search (PAEKS) which can resist keyword guessing attacks (KGA) provides a feasible approach for data sharing and searching in EMR systems. Specifically, a PAEKS scheme requires the sender to use the receiver’s public key when encrypting, which restricts the generated ciphertext to be searchable by only one specified receiver. If a sender wants to share a data with multiple receivers, the sender has to repeatedly encrypt the data for multiple receivers using the public keys of different receivers. For the receiver, the same issue also exists in the trapdoor generation phase. Therefore, the traditional PAEKS is not suitable for EMR systems involving multiple senders and multiple receivers because of a large number of repeated computations. In this work, we present a practical scheme called multi-user keyword-field-free conjunctive searchable encryption (MU-KFFCSE). In order to achieve KGA-resistant searchable encryption between senders and receivers, we use receiver servers and sender servers such that the computation cost and communication cost of the ciphertext (trapdoor) generation phase are independent of the number of receivers (senders). The proposed scheme also supports flexible searchable encryption with keyword-field-free conjunctive utilizing polynomial technology, which not only increases the accuracy of search results, but also eliminates the limitation of fields. We prove that our scheme satisfies ciphertext indistinguishability (CI) and trapdoor indistinguishability (TI) security without random oracle. Theoretical analysis and experimental results show that our scheme is efficient in terms of computation cost and storage cost compared with existing schemes.

As a crucial component of intelligent transportation systems, VANETs are essential for enhancing road safety and enabling efficient traffic management. To ensure secure communication, vehicles often use pseudonyms to protect their identity privacy. However, unconditional anonymity can hinder accountability, making it very necessary to provide conditional privacy protection for vehicles. The conditional privacy-preserving technology not only protects the identity privacy of legitimate vehicles, but also can trace the real identity of malicious vehicles. Some existing schemes lack conditional privacy protection or have large computation and communication costs, which makes them unsuitable for resource-constrained VANETs environments. Hence, we improve the current schnorr-based aggregate signature by eliminating bilinear pairing operations, optimizing the aggregation procedure for batch verification and propose a lightweight certificateless-based aggregate signature scheme (ECPP-CLAS) for VANETs. In our scheme, the aggregation enables multiple signatures to be compressed into an aggregated signature and verified simultaneously, thereby reducing communication consumption, trusted entity generates the pseudonym for the corresponding vehicle through special construction to meet the conditional privacy-preserving requirement. The security analysis and performance evaluation show that our proposed scheme can meet the expected security objectives and lightweight requirements.

The cyclical and continuous working characteristics ofInternet of Things(IoT) devices make a large amount of the same or similar data, which can significantly consume storage space. To solve this problem, various secure data deduplication schemes have been proposed. However, existing deduplication schemes only perform deduplication based on data similarity, ignoring the internal connection among devices, making the existing schemes not directly applicable to parallel and distributed scenarios like IoT. Furthermore, since secure data deduplication leads to multiple users sharing same encryption key, which may lead to security issues. To this end, we propose a device relationship-based IoT data deduplication scheme that fully considers the IoT data characteristics and devices internal connections. Specifically, we propose a device relationship prediction approach, which can obtain device collaborative relationships by clustering the topology of their communication graph, and classifies the data types based on device relationships to achieve data deduplication with different security levels. Then, we design a similarity-preserving encryption algorithm, so that the security level of encryption key is determined by the data type, ensuring the security of the deduplicated data. In addition, two different data deduplication methods, identical deduplication and similar deduplication, have been designed to meet the privacy requirement of different data types, improving the efficiency of deduplication while ensuring data privacy as much as possible. We evaluate the performance of our scheme using five real datasets, and the results show that our scheme has favorable results in terms of both deduplication performance and computational cost.

Abstract A confidential reporting system (CRS) allows reporters to report concerns or problems in confidence without the fear of blame or reprisals. Nevertheless, privacy has been the primary concern of reporters. In this paper, we propose a privacy-preserving confidential reporting system with designated reporters (PPCRS-DR) to protect the privacy of reporters and the confidentiality of reports. Our PPCRS-DR provides the following interesting features: (1) for an event, an auditor can designate a reporter to report; (2) an auditor can neither see the report nor know the reporter’s identity from an encrypted report if the reporter is not the designated one; (3) when an auditor is unavailable, he/she can temporarily designate a delegatee to collect and review reports on behalf of him/her. We formalize both the definition and security model of our PPCRS-DR, and propose a concrete construction. Furthermore, the security of the proposed PPCRS-DR is formally proven. The implementation shows that it is efficient. The novelty is to implement flexible decryption delegation of CRSs and protect reporters’ privacy.

E-healthcare as a significant facet of the Internet of Things (IoT) relies on wearable devices to continuously monitor users’ vital signals for health-related purposes. The sensitive and vast nature of the collected data necessitate secure encryption and storage on the cloud. Simultaneously, there is a need to share these data for healthcare purposes. How to balance the privacy and usability of these data is a challenging problem in the e-healthcare applications. A central problem arose from the continuous data collection is how to effectively share the data collected in one specific time period when users are unwell. We formalize it as the sequential data sharing problem. This problem appears in various IoT applications apart from e-healthcare, such as video surveillance. In this paper, we explain why all existing solutions cannot address the above problem. Then, we propose a novel sequential data sharing system (SDSS), where the data encrypted at any specific time period can be efficiently shared. We first present a practical construction of SDSS that supports securely sharing data within one specific time period in a symmetric manner. The decryption key are retrieved sequentially by utilizing the shared key and hash function. All involved calculations in the system are lightweight. Data pertaining to other non-selected time periods remain unknown. We then extend the SDSS to a multiple-range version, enabling simultaneous sharing data for multiple specific time periods, and show an example. We formalize the definition of security models and analyze the security of our systems. Finally, we evaluate the performance of our systems using SHA-256 and AES-256. Experimental results demonstrate that our systems are highly efficient. It takes less than 1 millisecond to encrypt 100KB data and less than 0.4 milliseconds to decrypt the corresponding cipher data. Our proposed systems provide a solution to balance the privacy and usability in the context of sequentially collected data. We believe that this work will enhance the adoption and practicality of IoT applications.

Combining a fog layer to aggregate and process data for smart grids is a straightforward approach, yet it inevitably leads to trust issues and audition difficulty. Most existing data-sharing architectures did not consider the copious meter–fog communication and fog–cloud bulk data transmission simultaneously, or they relay the trustworthiness of the fog nodes on a single center. In this article, we design a meter–fog–cloud-blockchain data-sharing architecture for smart grids where the fog nodes are not only data relay stations but also semitrusted local data processing points, and the dual blockchains are responsible for device key management and data integrity audit, respectively. Moreover, a certificateless aggregate signcryption between fog and smart meters is designed, and the data sharing between servers is based on an authenticated key agreement mechanism to achieve optimal efficiency overall. Detailed security proofs are demonstrated and performance results show the practicality and efficiency of our data-sharing scheme.

Abstract SM9 is a Chinese cryptography standard, which includes a set of identity-based cryptographic schemes over pairings. SM9 identity-based signature scheme (SM9-IBS) was standardized by ISO/IEC and has been widely used in many real-world applications such as blockchain. Nevertheless, the signing algorithm of SM9-IBS suffers from several heavy calculations (e.g. pairings, scalar multiplications in groups), which might be a bottleneck for lightweight devices such as sensors. In this paper, we modify the SM9-IBS scheme slightly to support fast signing. In order to achieve this, we make the use of online/offline methodology and propose a new online/offline IBS scheme based on SM9. The proposed scheme is proved to be EUF-sID-CMA secure and is about 99% faster than SM9-IBS in terms of signature generation. Precisely, the time cost of online signing is <1 ms. Our scheme is appropriate for the Internet of Things. The theoretical analysis and demonstration show that the proposed scheme is comparable to existing efficient online/offline IBS schemes.

Cloud computing is considered as one of the most prominent paradigms in the information technology industry, since it can significantly reduce the costs of hardware and software resources in computing infrastructure. This convenience has enabled corporations to efficiently use the cloud storage as a mechanism to share data among their employees. At the first sight, by merely storing the shared data as plaintext in the cloud storage and protect them using an appropriate access control would be a nice solution. This is assuming that the cloud is fully trusted for not leaking any information, which is impractical as the cloud is owned by a third party. Therefore, encryption is mandatory, and the shared data will need to be stored as a ciphertext using an appropriate access control. However, in practice, some of these employees may be malicious and may want to deviate from the required sharing policy. The existing protection in the literature has been explored to allow only legitimate recipients to decrypt the contents stored in the cloud storage, but unfortunately,no existing workdeals with issues raised due to the presence of malicious data publishers. Malicious data publishers construct data following the given policy, but the ciphertexts can actually be decrypted by unauthorized users without valid keys, or simply, anyone else who is unauthorized. The impact of the involvement of malicious data publishers is detrimental, as it may damage intellectual properties from the corporations. Therefore, it remains an elusive research problem on how to enable a sound approach to resolve the issue when malicious data publishers are involved in the system, which is a very practical question. In this work, we presenta new direction of researchthat can cope with the presence of malicious data publishers. We resolve the aforementioned problem by proposing the notion of Sanitizable Access Control System (SACS), which is designed for a secure cloud storage that can also resist against malicious data publishers. We define the threat model and its formal security model, as well as its design and scheme which is based on$q$q-Parallel Bilinear Diffie-Hellman Exponent Assumption. We provide the security proof of our construction as well as its performance analysis. We believe that this work has opened a new area of research which has never been explored before, even though it is very practical. Therefore, this work will enhance the adoption of secure cloud storage in practice.

Broadcast encryption provides a promising technique of data access control for specified users in cloud computing. A data uploader can generate a ciphertext for a set of chosen users such that only the intended users are able to access the data. However, with the rapidly increasing of collaboration between users, it is desired to extend the receiver set to grant decryption right for more users. The existing broadcast encryption systems cannot support receiver extension. In this article, we for the first time take this problem into consideration and give a solution. We take the merits of identity-based cryptosystem and propose a notion of EIBBE: a flexible data access control with receiver extendable for cloud computing based on broadcast encryption. It allows the authorized user to extend the receiver set$S$stated in the IBBE ciphertext by adding a new receiver set$S^{\prime }$without re-encryption. Both the users in$S$and$S^{\prime }$can access the data successfully. Moreover, the data uploader determines the maximum number of extended receivers. We then give a concrete construction of EIBBE and provide a rigorous security analysis of our proposed scheme. Finally, we demonstrate the scheme's efficiency and feasibility.

Filtering refers to an operation to determine whether the concerned data should be accepted and transferred, or be blocked and marked as a malicious traffic flow. It mitigates the inter-domain bandwidth overhead, local computational cost and storage cost for data identification. In many sensitive applications, the identity of the data provider needs to be hidden. This creates challenges how to filter the transmitted data packet with an encrypted form. It is non-trivial to hide this data provider's identity while enabling filtering, as the policy used as a matching criteria will need to determine whether the data needs to be transferred or not without knowing the origin of that data. In this work, we designPPFilter, a privacy-aware encrypted filtering mechanism which allows the filtering to be conducted without the need to know the identity of the data provider. PPFilter achieves the integrity protection of the data packets and the provider privacy Level 3. PPFilter is built on top of a novel notion calledidentity-based encryption with sender search (IESS), which supports anonymous sender identity in an encrypted searching. We present a provably secure IESS instantiation, and apply it to achieve a PPFilter protocol. PPFilter allows the data provider's identity to be hidden from both the transferred data and policy while enabling the filtering capability, which solves the aforementioned problem. The analysis and evaluation show that PPFilter maintains cost-reasonable filtering while preserving provider privacy, and hence it guarantees its practicality.

In the identity-based broadcast encryption (IBBE), only these users whose identities are chosen in the ciphertext computing can decrypt the encrypted message. In this paper, we introduce an extension of IBBE, namely Identity-Based Broadcast Encryption for Inner Product (IBBE-IP), where message encryption is replaced by inner product encryption (IPE) introduced by Abdalla et al. (PKC 2015). Precisely, in the IBBE-IP, the private key is associated with a pair of an identity and a vector (ID,y→)⁠. The user with private key of (ID,y→) can decrypt the encrypted vector x→ for an identity set S selected by the encryptor and learn the inner product 〈x→,y→〉 if and only if ID∈S⁠. Differing from the IBBE, the decryption in the IBBE-IP yields the inner product associated with the encrypted vector without leaking any information of the vector. The encrypted vector is protected as long as the number of selected identities is less than their length. We present a construction of IBBE-IP with constant-size private keys and it supports unbounded private key queries, which was unachieved in the previous works of IPE in the public-key setting. The security of our proposed scheme is proved in the random oracle model.

A revocable ID-based broadcast encryption scheme allows an authorized third party to revoke any receiver (decryptor) from the initial receiver set S of the original broadcast ciphertext without the need of decryption. However, the existing revocable ID-based broadcast encryption schemes in the literature cannot fully preserve the receiver privacy and have a large size of ciphertext when the revoked user sets are large. To solve these problems, in this paper, we propose a novel scheme: fully privacy-preserving ID-based broadcast encryption with authorization. Our scheme allows an authorized party to dynamically handle the decryption rights of receivers via an authorized user set L without knowing the message and the identities of the initial receivers. Only those users who are both in S and L can decrypt the ciphertext successfully. The final ciphertext reveals nothing about the identity information of receivers and the authorized users. Our scheme achieves full collusion resistance and is applicable to anonymous data sharing where the receivers are decided by the authorized third party (or multiple authorized third parties) excluding the data owner. We show that our proposed scheme is provably secure under the defined security models in the random oracle model.

Abstract Centralized approaches are widely adopted to improve the qualities of outsourced services owing to its feature of efficient system management. Because the cloud is untrusted, data are usually encrypted before outsourcing. One of the interesting applications is searchable encrypted keywords, a well‐known cryptographic primitive that allows encryption while enabling search for keywords. However, achieving data retrieval without revealing privacy in a cloud‐based centralized system is still a challenging problem. In this paper, we introduce centralized approaches to searchable encryption and present a novel centralized system for retrieval services. In our system, the centralized manager can search and access all the encrypted data from authorized users, while each user can only search and access his or her own data. The system builds on a new cryptographic notion calledcentralized keyword search on encrypted data. We formalize its security model and propose a centralized keyword search on encrypted data construction that is featured by short ciphertext and search result verification. We further extend the construction for removing secure channel and enabling batch authentication on data legalities. The experiment demonstrates the performance of our proposals. Copyright © 2016 John Wiley & Sons, Ltd.