Forward and Backward Private Searchable Encryption with SGX

Searchable symmetric encryption (SSE) scheme allows a data owner to perform search queries over encrypted documents using symmetric cryptography. SSE schemes are useful in cloud storage and data outsourcing. Most of the SSE schemes in existing literature have been proved to leak a substantial amount of information that can lead to an inference attack. This paper presents, a novel leakage resilient searchable symmetric encryption with periodic updation (LRSSEPU) scheme that minimizes extra information leakage, and prevents an untrusted cloud server from performing document mapping attack, query recovery attack and other inference attacks. In particular, the size of the keyword vector is fixed and the keywords are periodically permuted and updated to achieve minimum leakage. Furthermore, our proposed LRSSEPU scheme provides authentication of the query messages and restricts an adversary from performing a replay attack, forged query attack and denial of service attack. We employ a combination of identity-based cryptography (IBC) with symmetric key cryptography to reduce the computation cost and communication overhead. Our scheme is lightweight and easy to implement with very little communication overhead.

: Cloud storage has now become widely used for the management of sensitive documents, thereby casting a huge shadow over the user’s right to privacy and the security of his data. One of the earliest encryption methods is AES, which is the most widely used among the rest of the traditional methods, and it still provides confidentiality only but not secure searching over the encrypted data. The new research introduces a QKD + AES-based Symmetric Searchable Encryption (SSE) system applicable to dynamic datasets and thus allowing secure keyword-based search without compromising the privacy. Under this scheme, QKD is the method used to send the AES encryption keys to the client and server securely, and thus the quantum adversaries cannot either intercept or manipulate the keys. After that, the AES encryption holds the data securely, while the SHA-256 hashing for the indexing of keywords is employed which allows an efficient and secure search over the encrypted data to be done. The system, besides giving forward privacy which forbids the connection of new data to previous searches, also provides backward privacy which assures that deleted entries will not be accessible in future queries.

Searchable symmetric encryption (SSE) has been proposed that enables the clients to outsource their private encrypted data onto the cloud server and later the data can be searched with limited information leakage. However, existing surveys have not covered most recent advances on SSE technique. To fill the gap, we make a survey on state-of-the-art representative SSE schemes in cloud environment. We mainly focus on dynamic SSE schemes with forward and backward privacy, two vital security elements to maintain query privacy during data update operations. Specifically, we discuss about SSE protocols based on query expressiveness, including single keyword search, conjunctive keyword search, range search, disjunctive keyword search and verifiable search. Finally, through comparison on query expressiveness, security and efficiency, we demonstrate the strengths and weaknesses of the existing SSE protocols.

We point out the risks of protecting relational databases via Searchable Symmetric Encryption (SSE) schemes by proposing an inference attack exploiting the structural properties of relational databases. We also show that record-injection attacks mounted on relational databases have worse consequences than their file-injection counterparts on unstructured databases. Moreover, we discuss some techniques to reduce the effectiveness of inference attacks exploiting the access pattern leakage existing in SSE schemes.

Searchable Symmetric Encryption (SSE) is a mechanism that facilitates search over encrypted data that is outsourced to an untrusted Server. SSE schemes offer practicality at the expense of some information leakage.The last two years, the first dynamic SSE (DSSE) schemes, i.e. schemes that support updates, that are both forward and backward private, were introduced. Two lines of design have been proposed. The first one contains the schemes that use an oblivious data structure, i.e. the Client hides the memory access pattern from the Server. This level of security comes at the expense of significant communication overheads as the oblivious memory access requires several communication roundtrips or the use of expensive primitives that limits the potential of practicality. The second line of design contains solutions that avoid oblivious data structures.In this paper, we introduce a new DSSE solution that offers both forward and the highest level of backward privacy. Our scheme is the first one that follows the first line of design and achieves this level of security with a constant and small number of communication roundtrips. We evaluate the scheme's performance and we show that it is practical.

Based on Sun et al. ’s multi-client symmetric searchable encryption (SSE) scheme (at ESORICS 2016), and combining Zhao’s identity-concealed authenticated encryption (CCS 2016), a new SSE scheme with multi-data-owner functionalities is proposed. By setting two key generation centers, our scheme first implements multi-data-owner SSE. In particular, compared with Sun et al. ’s scheme, the new scheme not only meets the same security requirements stated by them, but also further strengthens the securities of the same category relevant scheme by providing identity-concealment, authentication of data user to server and confidentiality of search token. The identity-concealment aims to provide privacy protection (Forward ID-Privacy) for data users by hiding their identity information, while the authentication is to resist the camouflage attack by applying certificate-based mechanism to our scheme. In particular, the confidentiality of the search token provides replay-attack-resistant by encrypting the plaintext search token generated by data user. While in other works, the adversary can employ the previously generated plaintext search tokens to force the server to perform the same search queries. Furthermore, by efficiency analysis, our scheme reaches almost the same level of efficiency as Sun et al. ’s scheme.

Cloud computing offers the possibility of providing suitable access within a network for a set of resources. Many users use different services for outsourcing their data within the cloud, saving and mitigating the local storage and other resources involved. One of the biggest concerns is represented by storing sensitive data on remote servers, which can be found to be extremely challenging within different situations related to privacy. Searchable Encryption (SE) represents a particular case of Fully Homomorphic Encryption (FHE) and at the same time represents a method composed from a set of algorithms meant to offer protection for users’ sensitive data, while it preserves the searching functionality on the server-side. There are two main types of SE: Searchable Symmetric Encryption (SSE), where the ciphertexts and trapdoors for searching are performed using private key holders, and Public Key Searchable Encryption (PKSE), in which a specific number of users have the public key based on which are capable of outputting ciphertexts and giving the possibility of producing the trapdoors by using the private key from the holder. In this article, we propose a searchable encryption system that uses biometric authentication. Additionally, biometric data are used in the trapdoor generation process, such that an unauthorized user cannot submit search queries. The proposed system contains three components: classic user authentication (based on username, password, and a message with a code using short message service (SMS), biometric authentication, and the searchable encryption scheme. The first two components can be seen as two-factor authentication (2FA), and the second component represents the initialization step of the searchable encryption scheme. In the end, we show and demonstrate that the proposed scheme can be implemented with success for medium to complex network infrastructures. We have granted special attention to the trapdoor function, which generates a value that can be used to perform the search process and search function that is based on the trapdoor pair for searching within the index structure. We provide the correctness and security proof of the operations, which gives us the guarantee that the cloud servers return the correct documents. Additionally, we discuss measuring the performance of the authentication scheme in terms of performance indicators, introducing two indicators for measuring purposes—namely, cloud average number of non-legitim the user actions for cloud purposes (CANNL) and cloud average number of legitim user actionsCANLU.

With the development of cloud computing, data sharing has a new effective method, i.e., outsourced to cloud platform. In this case, since the outsourced data may contain privacy, they only allow to be accessed by the authorized users. Encrypting the data before outsourcing is a commonly used approach, where the data owners only need to send the corresponding encryption key to the authorized users. However, in such approach it is difficult to use the data since the encrypted data obsoletes comprehensive search functionalities of plaintext keyword search. In this paper, we leverage the secure k-nearest neighbor to propose a secure dynamic searchable symmetric encryption scheme. Our scheme can achieve two important security features, i.e., forward privacy and backward privacy which are very challenging in Dynamic Searchable Symmetric Encryption (DSSE) area. In addition, we evaluate the performance of our proposed scheme compared with other DSSE schemes. The comparison results demonstrate the efficiency of our proposed scheme in terms of the storage, search and update complexity.

With the wide spread of Cloud service, users are outsourcing their data to the third party servers. When we delegate our data to the cloud servers, there is such a potential risk that the data stored in the servers is stolen. If the data are stored in the encrypted form, the damage caused by data theft is low because the data will not leak to other parties. However, a new problem arises, that is, users are not able to operate encrypted data, which loses the merit of cloud computing. To solve such a problem, searchable symmetric encryption(SSE) is proposed. SSE is a cryptographic protocol that can execute keyword search over encrypted documents without decrypting them. Secure Indexes is one of realizations of SSE that provides constant time keyword search per document with the help of pseudo-random function and Bloom filters. However, Secure Indexes dose not support addition and deletion of documents. Tekin and Sahin proposed an improved Secure Indexes scheme that supports addition and deletion by employing Bloom filter and counting Bloom filter. The drawback of their scheme is that these operations are implemented in user side, which is not desired in the cloud computing since the aim of cloud computing is to delegate as many operations as possible. This paper proposes new SSE scheme. The proposed scheme also employ counting Bloom filter, but provide more fine-grained operations compared to the scheme by Tekin and Sahin in the sense that the proposed scheme provides not only search documents but add and delete the elements of document. Moreover, these operations are executed in the server side. The performance of the proposed SSE is comparable to the existing scheme which provides constant time for search, add and delete per document. We also implemented this SSE scheme, and verified that the scheme performed well not only theoretically but also in practice.

Outsourcing medical data and their search services to a third party cloud have been a popular trend for many medical practices, because using healthcare cloud services can help cut down the cost of Electronic Health Records (EHR) systems in terms of front-end ownership cost and IT maintenance burdens. Healthcare cloud applications need searchable encryption with the following two capabilities for protecting data privacy and access privacy: (1) the healthcare providers need to share the encrypted data with authorized users and enable querying over encrypted data, and (2) they also need to keep the query keywords and associated search operations private such that healthcare data hosting service providers cannot gain access to unauthorized content or trace and infer sensitive data stored in the healthcare cloud. This survey paper describes the notion of searchable encryption (SE) in the context of healthcare applications and characterize the SE use cases into four scenarios in healthcare. Then we provide a comprehensive overview of the four representative SE techniques: searchable symmetric encryption (SSE), public key encryption with keyword search (PEKS), attribute-based encryption with keyword search (ABKS), and proxy re-encryption with keyword search (PRES) according to different EHR retrieving scenarios and requirements. We categorize and compare the different SE schemes in terms of their security, efficiency, and functionality. The survey is designed to benefit both experienced researchers in the computer science (CS) field and non-specialists who are domain scientists or healthcare professionals with limited CS and information security background. Thus, we are in favor of technological overview of the state of art searchable encryption models and the underlying key techniques, instead of detailed proofs and constructions of the respective SE algorithms. We describe how the existing SE schemes relate to and differ from one another, and point out the connections between the SE techniques and the security and privacy requirements of healthcare applications and the open research problems.

Searchable Symmetric Encryption (SSE) allows a client to search over the encrypted database, which protects privacy while maintaining the searchability of the data. Later, Dynamic SSE (DSSE) has been introduced, which supports the update of the encrypted database. However, most existing DSSE schemes either achieve less security level or support single keyword queries only. To tackle this problem, this thesis gives enhanced security definition and introduces several different DSSE schemes with enhanced security and supporting richer queries.

Searchable encryption allows us to perform a keyword search over encrypted data. However, we cannot efficiently perform some complex search (e.g., a wildcard search) with traditional searchable encryption schemes because they can deal with only equality matches. Our symmetric searchable encryption can deal with partial matches. This allows us to efficiently perform a wildcard search, partial match search, and so on. We also examine the feasibility of our scheme by experiments on a smartphone and tablet, and confirm our scheme can be used in these environments. Availability on portable devices will offer high convenience. Copyright © 2013 John Wiley & Sons, Ltd.

Existing Oblivious RAM protocols do not support the storage of data items of variable size in a non-trivial way. While the study of ORAM for items of variable size is of interest in and of itself, it is also motivated by the need for more performant and more secure Searchable Symmetric Encryption (SSE) schemes. In this article, we introduce the notion of weighted ORAM, which supports the storage of blocks of different sizes. We introduce a framework to build efficient weighted ORAM schemes, based on an underlying standard ORAM satisfying a certain suitability criterion. This criterion is fulfilled by various Tree ORAM schemes, including Simple ORAM and Path ORAM. We deduce several instantiations of weighted ORAM, with very little overhead compared to standard ORAM. As a direct application, we obtain efficient SSE constructions with attractive security properties.

Searchable symmetric encryption (SSE) enables users to efficiently search ciphertext in the cloud and ensures the security of encrypted data. Recent works show that forward security is an important property in dynamic SSE. Many forward secure searchable symmetric encryption (FSSE) schemes supporting single-keyword search have been proposed. Only a few SSE schemes can satisfy the forward security and support conjunctive keyword search at the same time, which are realized by adopting inefficient or complicated cryptography tools. Very recently, Hu proposed a novel construction to achieve conjunctive-keyword search, that is, using inner-product encryption (IPE) to design a conjunctive-keyword FSSE scheme. However, IPE scheme is a conceptually complex and low efficient scheme. In this paper, we use a more efficient cryptographic tool, asymmetric scalar-product-preserving encryption (ASPE), to design an efficient and secure conjunctive-keyword FSSE scheme. To improve practicality, we design our scheme to support multi-user setting. Our scheme achieves sub-linear efficiency, and can easily be used in any single-keyword FSSE scheme to obtain a conjunctive-keyword FSSE scheme supporting multi-user. Compared with the current conjunctive-keyword FSSE scheme, our scheme has a better update and search efficiency.

Although searchable encryption schemes allow secure search over the encrypted data, they mostly support conventional Boolean keyword search, without capturing any relevance of the search results. This leads to a large amount of post-processing overhead to find the most matching documents and causes an unnecessary communication cost between the servers and end-users. Such problems can be addressed efficiently using a ranked search system that retrieves the most relevant documents. However, existing state-of-the-art solutions in the context of Searchable Symmetric Encryption (SSE) suffer from either (a) security and privacy breaches due to the use of Order Preserving Encryption (OPE) or (b) non-practical solutions like using the two non-colluding servers. In this paper, we present a generic solution for multi-keyword ranked search over the encrypted cloud data. The proposed solution can be applied over different symmetric searchable encryption schemes. To demonstrate the practicality of our technique, in this paper we leverage the Oblivious Cross Tags (OXT) protocol of Cash et al. (2013) due to its scalability and remarkable flexibility to support different settings. Our proposed scheme supports the multi-keyword search on Boolean, ranked and limited range queries while keeping all of the OXT’s properties intact. The key contribution of this paper is that our scheme is resilience against all common attacks that take advantage of OPE leakage while only a single cloud server is used. Moreover, the results indicate that using the proposed solution the communication overhead decreases drastically when the number of matching results is large.