Searchable Encryption for Healthcare Clouds: A Survey

Efficient and secure searchable encryption protocol for cloud-based Internet of Things

Proxy re-encryption with keyword search

Searchable encryption schemes provide an important mechanism to cryptographically protect data while keeping it available to be searched and accessed. In a common approach for their construction, the encrypting entity chooses one or several keywords that describe the content of each encrypted record of data. To perform a search, a user obtains a trapdoor for a keyword of her interest and uses this trapdoor to find all the data described by this keyword. We present a searchable encryption scheme that allows users to privately search by keywords on encrypted data in a public key setting and decrypt the search results. To this end, we define and implement two primitives: public key encryption with oblivious keyword search (PEOKS) and committed blind anonymous identity-based encryption (IBE). PEOKS is an extension of public key encryption with keyword search (PEKS) in which users can obtain trapdoors from the secret key holder without revealing the keywords. Furthermore, we define committed blind trapdoor extraction, which facilitates the definition of authorisation policies to describe which trapdoor a particular user can request. We construct a PEOKS scheme by using our other primitive, which we believe to be the first blind and anonymous IBE scheme. We apply our PEOKS scheme to build a public key encrypted database that permits authorised private searches, i.e., neither the keywords nor the search results are revealed.

Public key encryption with keyword search (PKES) enables senders to send encrypted data to a Freceiver like traditional public key encryption (PKE) schemes. The difference between PKES and PKE is that the receiver in PKES can search on the encrypted data which is stored on the third-party server (like a cloud storage server). As far as we know, most of the existed PKES schemes are based on bilinear map, so they are costly in computation and hard to be used in practice. In this paper, we construct a PKES scheme based on factoring, it's computational efficient and secure. The public parameters in our scheme is also short, we just need a public modules and a random element of the set of integers.

We survey the notion of provably secure searchable encryption (SE) by giving a complete and comprehensive overview of the two main SE techniques: searchable symmetric encryption (SSE) and public key encryption with keyword search (PEKS). Since the pioneering work of Song, Wagner, and Perrig (IEEE S&P '00), the field of provably secure SE has expanded to the point where we felt that taking stock would provide benefit to the community.The survey has been written primarily for the nonspecialist who has a basic information security background. Thus, we sacrifice full details and proofs of individual constructions in favor of an overview of the underlying key techniques. We categorize and compare the different SE schemes in terms of their security, efficiency, and functionality. For the experienced researcher, we point out connections between the many approaches to SE and identify open research problems.Two major conclusions can be drawn from our work. While the so-called IND-CKA2 security notion becomes prevalent in the literature and efficient (sublinear) SE schemes meeting this notion exist in the symmetric setting, achieving this strong form of security efficiently in the asymmetric setting remains an open problem. We observe that in multirecipient SE schemes, regardless of their efficiency drawbacks, there is a noticeable lack of query expressiveness that hinders deployment in practice.

Attribute-based encryption with keyword search (ABEKS) is a novel cryptographic paradigm that can be used to implement fine-grained access control and retrieve ciphertexts without disclosing the sensitive information. It is a perfect combination of attribute-based encryption (ABE) and public key encryption with keyword search (PEKS). Nevertheless, most of the existing ABEKS schemes have limited search capabilities and only support single or simple conjunctive keyword search. Due to the weak search capability and inaccurate search results, it is difficult to apply these schemes to practical applications. In this paper, an efficient expressive ABEKS (EABEKS) scheme supporting unbounded keyword universe over prime-order groups is designed, which supplies the expressive keyword search function supporting the logical connectives of “AND” and “OR”. The proposed scheme not only leads to low computation and communication costs, but also supports unbounded keyword universe. In the standard model, the scheme is proven to be secure under the chosen keyword attack and the chosen plaintext attack. The comparison analysis and experimental results show that it has better performance than the existing EABEKS schemes in the storage, computation and communication costs.

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.

Currently, the security situation of data security and user privacy protection is increasingly serious in cloud environment. Ciphertext data storage can prevent the risk of user's privacy disclosure. But how to search keyword on ciphertext data without revealing keyword information becomes a new challenge. Searchable encryption (SE) is put forward for this reason, which can be used to realize ciphertext-search directly. In terms of multi-user data sharing, public-key encryption with keywords search (PEKS) is more widely used than symmetric searchable encryption. PEKS has been widely studied and developed by researchers in recent years. However, the existing PEKS scheme often lacks flexible access policy. Therefore, combining the advantage of policy control on attribute-based encryption (ABE), and as that the bilinear pairing related assumption is fragile in post-quantum era, lattice-based cryptography is considered as one of secure encryption technology against quantum attack. With this background, in this paper, we give a keyword-searchable ABE scheme based on the hardness of lattice problems, our scheme supports flexible attribute control policy by integrating ABE and PEKS, and the security of new scheme is proved under the learning with errors (LWE) assumption. As lattice-based cryptographic technology is currently thought to be resistant to quantum attacks, so the new scheme has stronger security in a quantum era.

Driven by cloud computing technologies, public-key encryption with keyword search (PEKS) is becoming a common practice from aspects of the Industrial Internet of Things, smart healthcare, vehicular social networks, and so on. However, a dozen years of PEKS development is accompanied by some security and privacy issues in the encrypted data search and access processes. The keyword guessing attack is a typical user privacy threat model, that is, an adversary could guess the user’s retrieval keyword given a search trapdoor. On the other hand, the emergence of quantum computers make traditional PEKS schemes no longer secure. Although scholars put forward some postquantum secure PEKS schemes, these schemes are based on lattice cryptography with a larger key size. To the best of our knowledge, there is no quantum-resist PEKS scheme established on elliptic curve cryptography. This article utilizes PEKS with designated tester primitive and quantum resistance of isogeny. Then, we put forward a postquantum searchable encryption scheme named Isoga, which fights against keyword guessing attacks. We prove Isoga’s searchable ciphertext security and trapdoor indistinguishability under isogeny-related difficult assumptions. Performance evaluation indicates that the Isoga scheme is more practical in the quantum environment, considering seven schemes’ security properties, communication cost, and computing overload among.

The emergence of public-key encryption with keyword search (PEKS) has provided an elegant approach to enable keyword search over encrypted content. Due to its high computational complexity proportional to the number of intended receivers, the trivial way of deploying PEKS for data sharing with multiple receivers is impractical, which motivates the development of a new PEKS framework for broadcast mode. However, existing works suffer from either the vulnerability to keyword guessing attacks (KGA) or high computation and communication complexity. In this work, a new primitive for keyword search in broadcast mode, named broadcast authenticated encryption with keyword search (BAEKS), is introduced, in which the sender not only encrypts the keyword but also authenticates it, eliminating the threats of KGA. Moreover, on top of keyword privacy, we formalize the notion of user anonymity (or key privacy) for BAEKS, which echoes the notion of key privacy for public-key encryption introduced by Bellare et al. (ASIACRYPT’01). We present a practical BAEKS construction that achieves all the desirable features, including keyword privacy of both searchable ciphertext and trapdoor, KGA-resistance, receiver anonymity of both searchable ciphertext and trapdoor, and universal keyword set scalability. Moreover, the trapdoor of our scheme achieves constant computation and communication cost, making it more suitable for broadcast mode where trapdoors are generated by multiple receivers in the search operations. The security of our scheme is proved under the standard DBDH assumption.

In this paper, we study the problem of secure integrating public key encryption with keyword search (PEKS) with public key data encryption (PKE). We argue the previous security model is not complete regarding keyword privacy and the previous constructions are secure only in the random oracle model. We solve these problems by first defining a new security model, then give a generic construction which is secure in the new security model without random oracles. Our construction is based on secure PEKS and tag-KEM/DEM schemes and achieves modular design. We also give some applications and extensions for our construction. For example, instantiate our construction with proper components, we have a concrete scheme without random oracles, whose performance is even competitive to the previous schemes with random oracles.

Abdalla et al.[1, 6] proposed a transform of an anonymous IBE (A-IBE) scheme to a PEKS (Public key encryption with keyword search) scheme. Boneh et al. proposed a transform of a PEKS scheme to an A-IBE scheme for only one-bit message. A transform for constructing an A-IBE scheme for polynomially many-bit message by using a PEKS scheme has not been proposed yet. To construct a transform from any PEKS scheme to an A-IBE scheme for a polynomially many-bit message, we firstly define a multiple PEKS (mPEKS) scheme and show that a mPEKS scheme can be constructed from a PEKS scheme. We also prove that if a PEKS scheme is confidential, so is the resulting mPEKS scheme. We then provide a transform from a mPEKS scheme to an A-IBE scheme for a polynomially many-bit message.

Witness-based searchable encryption with optimal overhead for cloud-edge computing

The Snowden incident illustrates that an adversary may launch an algorithm substitution attack (ASA) by tampering with the algorithms of protocol participants to obtain users' secret information. A measure against ASA is to equip the protocol participants with cryptographic reverse firewalls (CRF). Public key encryption with keyword search (PEKS) as a cryptographic primitive allows users to search encrypted file in cloud servers while ensuring the security of the original file. The existing CRF constructions for PEKS does not consider the trust level of CRFs, leaving honest-but-curious CRF to deal with trapdoors that should be sent in the secure channels, which brings new security risks. This paper firstly introduces the notion of malleable designated tester public key encryption with keyword search (M-DPEKS). Based on M-DPEKS, we propose the generic construction of public key encryption with keyword search with cryptographic reverse firewalls to overcome the privacy leakage issue in cloud storage. Security proof indicates the generic construction is secure against ASA. Lastly, we instantiate the generic construction with a concrete M-DPEKS scheme and analyze the computation cost and communication overhead to evaluate the efficiency.

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.