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Data outsourcing has become an industry trend with the popularity of cloud computing. How to search data securely and efficiently has received unprecedented attention. Dynamic Searchable Symmetric Encryption (DSSE) is an effective method to solve this problem, which supports file updates and keyword-based searches over encrypted data. Unfortunately, most existing DSSE schemes have privacy leakages during the addition and deletion phases, thus proposing the concepts of forward and backward privacy. At present, some secure DSSE schemes with forward and backward privacy have been proposed, but most of these DSSE schemes only achieve single-keyword query in the single-client setting, which seriously limits the application in practice. To solve this problem, we propose a multi-client and multi-keyword searchable symmetric encryption scheme with forward and backward privacy (MMKFB). Our scheme focuses on the multi-keyword threshold queries in the multi-client setting, which is a new pattern of multi-keyword search realized with the help of additive homomorphism. And performance analysis and experiments demonstrate that our scheme is more practical for use in small and medium size databases. Especially when a large number of files are updated at once, our scheme has advantages over some existing DSSE schemes in terms of computational efficiency and client storage overhead. [ABSTRACT FROM AUTHOR]

In this paper, we design and consider a new digital signature scheme with an evolving secret key, using random q-ary lattices as its domain. It is proved that, in addition to offering classic eu-cma security, the scheme is existentially forward unforgeable under an adaptive chosen message attack (fu-cma). We also prove that the secret keys are updated without revealing anything about any of the keys from the prior periods. Therefore, we design a polynomial-time reduction and use it to show that the ability to create a forgery leads to a feasible method of solving the well-known small integer solution (SIS) problem. Since the security of the scheme is based on computational hardness of a SIS problem, it turns out to be resistant to both classic and quantum methods. In addition, the scheme is based on the “Fiat-Shamir with aborts” approach that foils a transcript attack. As for the key-updating mechanism, it is based on selected properties of binary trees, with the number of leaves being the same as the number of time periods in the scheme. Forward security is gained under the assumption that one out of two hash functions is modeled as a random oracle. [ABSTRACT FROM AUTHOR]

Dynamic searchable symmetric encryption(DSSE) combines dynamic update with searchable encryption, allowing users to not only achieve keyword retrieval, but also dynamically update encrypted data stored on semi-trusted cloud server, effectively protecting user’s privacy. However, the majority of existing DSSE schemes exhibit inefficiencies in practical applications because of their complex structure. In addition, to store the status of keywords, the storage requirements of the client increase proportionally with the number of keyword/document pairs. Therefore, the client storage will be overwhelmed when confronted with a substantial increase in the volume of keyword/document pairs. To solve these issues, we propose a practical efficient dynamic searchable symmetric encryption scheme with lightweight clients—CoD-DSSE. A novel index structure similar to a chest of drawers is proposed in CoD-DSSE, which allows users to efficiently search all document indexes through XOR operations and keeps the keyword status on the server to lightweight clients. Furthermore, we use a random number generator to construct new search tokens for forward security and achieve backward security by using a Bloom filter to store the deleted document index, which can significantly reduce communication costs. The experimental and security analyses show that CoD-DSSE is efficient and secure in practice.

Ciphertext-Policy Attribute-Based Searchable Encryption (CP-ABSE) is one of the most suitable encryption mechanisms in cloud environments for its fine-grained access structure and keyword retrieval capability over the ciphertext. However, in the CP-ABSE schemes, guaranteeing the forward security of the outsourced cloud data and securely deleting those no longer needed data without relying on the cloud are challenging problems. To handle such challenges, we propose a Puncturable CP-ABSE (Pun-CP-ABSE) scheme that achieves self-controlled data deletion with a fine-grained access structure under the searchable mechanism. The data owner punctures the trapdoor to accomplish the data deletion. Then, the deletion process does not need to communicate with a trusted third party and can guarantee forward security. After the puncturation, the cloud server can no longer search for the corresponding ciphertext. Furthermore, we prove the Pun-CP-ABSE scheme is secure against the Chosen-Plaintext Attack (CPA) and Chosen-Keyword Attack (CKA). We have also implemented the Pun-CP-ABSE scheme to show its efficiency and feasibility.

Lightweight devices in the Internet of Things (IoT) typically need to store massive data on a cloud server with strong processing and storage capabilities for later retrieval and usage. Since these data contain the participant’s sensitive information, they cannot be delivered directly to the cloud server. Public-key Encryption with Keyword Search (PEKS) allows customers to search for target encrypted files using keywords. However, the majority of PEKS implementations are unable to repel malicious quantum-capable attackers. And with regard to forward security, they must search for many rounds to obtain the necessary data. To resolve these concerns, we propose a comprehensive Inner Product Outsourcing PEKS system (IPO-PEKS) with forward security based on LWE assumptions, which raises search efficiency by allowing authorized clients to find the information they desire in a single round and achieves more fine-grained searches. Furthermore, we offer an inner product outsourcing calculation technique that allows the server to compute the inner product result without knowing the details of both parties in order to conceal the relevant privacy data of transmitting and decryption states. The paradigm can be utilized for efficient state transition through the use of parallel computing to accomplish the target of one round of iteration.

Dynamic searchable symmetric encryption (DSSE) enables searches over encrypted data as well as data dynamics such as flexible data addition and deletion operations. A major security concern in DSSE is how to preserve forward and backward privacy, which are typically achieved by removing the linkability between the newly added data and previous queries, and between the deleted data and future queries, respectively. After information leakage types were formally defined for different levels of backward privacy (i.e., Type-I, II, III), many backward private DSSE schemes have been constructed under the definitions. However, we observed that the backward privacy can be violated by leveraging additional secondary leakage, which is typically leaked in specific constructions of schemes in spite of their theoretical guarantees. In this paper, in order to understand the security gap between the theoretical definitions and practical constructions, we conduct an in-depth analysis of the root cause for the secondary leakage, and demonstrate how it can be abused to violate Type-II backward privacy (e.g., the exposure of the deletion history) of DSSE constructions in practice. We then propose a novel Type-II backward private DSSE scheme based on Intel SGX, which is resilient to the secondary leakage abuse attack. According to the comparative analysis of our scheme with the state-of-the-art SGX-based DSSE schemes, Bunker-B (EuroSec'19) and SGX-SE1 (ACNS'20), our scheme shows higher efficiency in terms of the search latency with a negligible utility loss under the same security level (cf. Bunker-B) while showing similar efficiency with a higher security level (cf. SGX-SE1). Finally, we formally prove that our scheme guarantees Type-II backward privacy. [ABSTRACT FROM AUTHOR]

Logging is a key mechanism in the security of computer systems. Beyond supporting important forward security properties, it is critical that logging withstands both failures and intentional tampering to prevent subtle attacks leaving the system in an inconsistent state with inconclusive evidence. We propose new techniques combining forward security with crash recovery for secure log data storage. As the support of specifically forward integrity and the online nature of logging prevent the use of conventional coding, we propose and analyze a coding scheme resolving these unique design constraints. Specifically, our coding enables forward integrity, online encoding, and most importantly a constant number of operations per encoding. It adds a new log item by ing it to k cells of a table. If up to a certain threshold of cells is modified by the adversary, or lost due to a crash, we still guarantee recovery of all stored log items. The main advantage of the coding scheme is its efficiency and compatibility with forward integrity. The key contribution of the paper is the use of spectral graph theory techniques to prove that k is constant in the number n of all log items ever stored and small in practice, e.g., k = 5. Moreover, we prove that to cope with up to \(\sqrt {n}\) modified or lost log items, storage expansion is constant in n and small in practice. For k = 5, the size of the table is only 12% more than the simple concatenation of all n items. We propose and evaluate original techniques to scale the computation cost of recovery to several GBytes of security logs. We instantiate our scheme into an abstract data structure which allows to either detect adversarial modifications to log items or treat modifications like data loss in a system crash. The data structure can recover lost log items, thereby effectively reverting adversarial modifications. [ABSTRACT FROM AUTHOR]

In this paper, we design and consider a new digital signature scheme with an evolving secret key, using random q-ary lattices as its domain. It is proved that, in addition to offering classic eu-cma security, the scheme is existentially forward unforgeable under an adaptive chosen message attack (fu-cma). We also prove that the secret keys are updated without revealing anything about any of the keys from the prior periods. Therefore, we design a polynomial-time reduction and use it to show that the ability to create a forgery leads to a feasible method of solving the well-known small integer solution (SIS) problem. Since the security of the scheme is based on computational hardness of a SIS problem, it turns out to be resistant to both classic and quantum methods. In addition, the scheme is based on the "Fiat-Shamir with aborts" approach that foils a transcript attack. As for the key-updating mechanism, it is based on selected properties of binary trees, with the number of leaves being the same as the number of time periods in the scheme. Forward security is gained under the assumption that one out of two hash functions is modeled as a random oracle.

A deterministic random bit generator (DRBG) generates pseudorandom bits from an unpredictable seed, i.e., a seed drawn from any random source with sufficient entropy. The current paper formalizes a security notion for a DRBG, in which an attacker may make any legal sequence of requests to the DRBG and sometimes compromise the DRBG state, but should still not be able to distingush DRBG outputs from ideal random bits. The paper proposes XDRBG, a new DRBG based on any eXtendable Output Function (XOF) and proves the security of the XDRBG in the ideal-XOF model. The proven bounds are tight, as demonstrated by matching attacks. The paper also discusses the security of XDRBG against quantum attackers. Finally, the paper proposes concrete instantiations of XDRBG, employing either the SHAKE128 or the SHAKE256 XDRBG. Alternative instantiations suitable for lightweight applications can be based on ASCON.

Remote sensing is considered to be a key technology for the development of smart cities. By analysing the data obtained by remote sensing, it is effective to manage and develop smart cities. However, with the rapid urbanisation and the increase in data capacity, how to store and retrieve remote sensing data which have more potential value and privacy with a more effective and safe method has become an imminent issue. In this paper, we propose an efficient verifiable and dynamic multi-keyword searchable encryption scheme for remote sensing data in smart cities. Moreover, we construct a double-chain index to support a multi-keyword search, where the Verification Index Chain is used to identify the users and the Keyword Index Chain is used to store the information of keywords. In addition, we adopt extended bitmap technology to realise update operations and verify the correctness and integrity of the search results. Experiments show that compared to the related existing schemes, the search time of the proposed scheme is reduced by 35% at most, the verification time is reduced by 14% at most and the update time is reduced by 57% at most. [ABSTRACT FROM AUTHOR]

With the continuous development of the Internet of Things (IOT) and cloud computing, smart devices are playing an increasingly important role in users' daily life. Dynamic searchable symmetric encryption (DSSE) schemes are popular on smart devices because of their efficient retrieval performance and low computational overhead. Traditional DSSE with forward update privacy and backward security can resist file injection attack and statistical inference attack. However, it is high cost and not suitable for smart devices due to large local storage and low storage capacity. To achieve forward update privacy, we design a novel index structure called RC-II (Inverted Index with Retrieve Control) for search control which improves the security of DSSE. Besides, we combine on and off-chain to decrease client's local storage to a constant. Specifically, we transfer a significant amount of local overhead to the service peers off blockchain. We solve the trust problem between the client and the service by putting authentication data on blockchain. Compared with the state-of-the-art schemes, our scheme has a constant client storage overhead and an excellent retrieval performance which provides guarantee for smart devices under IOT environment. [ABSTRACT FROM AUTHOR]

Public key encryption with keyword search is a promising primitive which enables search over encrypted data in secure data outsourcing services. In traditional construction, the associated keywords may be recovered from a given trapdoor by a malicious server through keyword guessing attacks. Therefore, the notion of public-key authenticated encryption with keyword search (PAEKS) was introduced, where a sender encrypts (and authenticates) the keywords using a receiver's public key and its secret key. In this paper, we consider the forward security for PAEKS and introduce a new primitive: forward secure public-key authenticated encryption with keyword search (FS-PAEKS), which captures the information leakage risk from previously issued queries due to the updates on the outsourced data. Technically, we embed a non-interactively agreed key into the cipher-keyword generation algorithm, and bind the cipher-keyword and the trapdoor with a set converted from algorithm-generation time. Finally, we present an efficient FS-PAEKS scheme supporting conjunctive query, and prove its forward security against chosen keyword attacks and keyword guessing attacks. To illustrate practical performance, we implement our FS-PAEKS and related PAEKS schemes based on Enron dataset in real cloud environment. [ABSTRACT FROM AUTHOR]

In cloud computing applications, users need to encrypt data locally before uploading it to the cloud server to ensure the security of private data. Searchable encryption technology allows users to directly search encrypted data on the server. Users with search permission can search ciphertext without limitation. In practical applications, the loss of user key and malicious attacks are easy to cause security threats to private data, and users should not keep the ability to retrieve data. This paper proposed a public-key searchable encryption scheme that supported the revocation of user retrieval rights. It divided the whole life cycle of the system into different periods. The ciphertext in the next period was evolved from the ciphertext in the last period. It revoked the user permission through the ciphertext evolution and time key distribution control. The scheme supports multi-keyword retrieval, reduces the computing cost, and cancels the search ability of all ciphertexts at the previous time to ensure the forward security of ciphertexts. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new digital signature primitive, called expander signature, and discuss its application in blockchain. The most promising advantage of expander signature is that a signer can generate all signatures at once using a powerful computer, and stores expander keys personally. Each time the signer wants some of his signatures to be verified, he releases the related expander key. No matter when or where, the signer can do this via a resource-limited device, for example, a personal portable terminal. We formally define the syntax and security of expander signature. Under our precisely defined security model, we give generic constructions of expander signature from both public key infrastructure-based and identity-based signature schemes. The security of our constructed expander signature schemes rigorously depends on the underlying public key signature schemes. The expander keys do not leak any information about the signer’s secret key and the size of the expander keys is constant no matter how many times the expander has been occurred. Finally, we give an application example of expander signature in blockchain.

Puncturable encryption allows recipients to revoke the decryption capability of ciphertexts flexibly, thus provides a fine-grained way to achieve forward security. So far, puncturable encryption and its variants have found many interesting applications, including the design of advanced cryptographic protocols and messaging systems. In this paper, we put forward the first generic construction of incremental symmetric puncturable encryption that can support an arbitrary number of punctures and achieve semantic security without random oracles. To this end, we introduce the notion of extended key-homomorphic puncturable PRF (EKHP-PRF) by abstracting the properties implicitly desired in many applications of almost key-homomorphic PRFs, which essentially removes the influence of errors due to almost key-homomorphism. Moreover, we present an efficient instantiation of EKHP-PRF based on a variant of Module Learning with Errors (MLWE) problem, namely non-uniform MLWE (NMLWE). Thus, we get the first lattice-based puncturable encryption featuring an arbitrary number of punctures in the standard model. [ABSTRACT FROM AUTHOR]

Dynamic searchable symmetric encryption (DSSE) enables searches over encrypted data as well as data dynamics such as flexible data addition and deletion operations. A major security concern in DSSE is how to preserve forward and backward privacy, which are typically achieved by removing the linkability between the newly added data and previous queries, and between the deleted data and future queries, respectively. After information leakage types were formally defined for different levels of backward privacy (i.e., Type-I, II, III), many backward private DSSE schemes have been constructed under the definitions. However, we observed that the backward privacy can be violated by leveraging additional secondary leakage, which is typically leaked in specific constructions of schemes in spite of their theoretical guarantees. In this paper, in order to understand the security gap between the theoretical definitions and practical constructions, we conduct an in-depth analysis of the root cause for the secondary leakage, and demonstrate how it can be abused to violate Type-II backward privacy (e.g., the exposure of the deletion history) of DSSE constructions in practice. We then propose a novel Type-II backward private DSSE scheme based on Intel SGX, which is resilient to the secondary leakage abuse attack. According to the comparative analysis of our scheme with the state-of-the-art SGX-based DSSE schemes, Bunker-B (EuroSec’19) and SGX-SE1 (ACNS’20), our scheme shows higher efficiency in terms of the search latency with a negligible utility loss under the same security level (cf. Bunker-B) while showing similar efficiency with a higher security level (cf. SGX-SE1). Finally, we formally prove that our scheme guarantees Type-II backward privacy.

Group signatures allow users to sign messages on behalf of a group without revealing authority is capable of identifying the user who generated it. However, the exposure of the user's signing key will severely damage the group signature scheme. In order to reduce the loss caused by signing key leakage, Song proposed the first forward-secure group signature. If a group signing key is revealed at the current time period, the previous signing key will not be affected. This means that the attacker cannot forge group signatures regarding messages signed in the past. To resist quantum attacks, many lattice-based forward-secure group signatures have been proposed. However, their key-update algorithm is expensive since they require some costly computations such as the Hermite normal form (HNF) operations and conversion from a full-rank set of lattice vectors into a basis.In this paper, we propose the group signature with forward security from lattice. In comparison with previous works, we have several advantages: Firstly, our scheme is more effective since we only need to sample some vectors independently from a discrete Gaussian during the key-update algorithm. Secondly, the derived secret key size is linear instead of quadratic with the lattice dimensions, which is more friendly towards lightweight applications. Anonymous authentication plays an increasingly critical role in protecting privacy and security in the environment where private information could be collected for intelligent analysis. Our work contributes to the anonymous authentication in the post-quantum setting, which has wide potential applications in the IoT environment.

Dynamic searchable encryption satisfies users' needs for ciphertext retrieval on semi-trusted servers, while allowing users to update server-side data. However, cloud servers with dynamically updatable data are vulnerable to information abuse and file injection attacks, and current public key-based dynamic searchable encryption algorithms are often complicated in construction and high in computational overhead, which is not efficient for practical applications. In addition, the client's storage costs grow linearly with the number of keywords in the database, creating a new bottleneck when the size of the keyword set is large. To solve the above problems, a dynamic searchable encryption scheme that uses a double-layer structure, while satisfying forward and backward security, is proposed. The double-layer structure maintains a constant client-side storage cost while guaranteeing forward and backward security and further reduces the algorithm overhead by avoiding bilinear pairings in the encryption and decryption operations. The analysis results show that the scheme is more advantageous in terms of security and computational efficiency than the existing dynamic searchable encryption scheme under the public key cryptosystem. It is also suitable for the big data communication environment. [ABSTRACT FROM AUTHOR]

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Abstract The explosive growth of big data is pushing forward the paradigm of cloud-based data store today. Among other, distributed storage systems are widely adopted due to their superior performance and continuous availability. However, due to the potentially wide attacking surfaces of the public cloud, outsourcing data store inevitably raises new concerns on user privacy exposure and unauthorized data access. Besides, directly introducing a centralized third-party authority for query authorization management does not work because it still can be compromised. In this paper, we propose a blockchain-assisted framework that can support trustworthy data sharing services. In particular, data owners allow to outsource their sensitive data to distributed systems in encrypted form. By leveraging smart contracts of blockchain, a data owner can distribute secret keys for authorized users without extra round interaction to generate the permitted search tokens. Meanwhile, such blockchain-assisted framework naturally solves the trust issues of query authorization. Besides, we devise a secure local index framework to support encrypted keyword search with forward privacy and mitigate blockchain overhead. To validate our design, we implement the prototype and deploy it at Amazon Cloud. Extensive experiments demonstrate the security, efficiency, and effectiveness of the blockchain-assisted design.

Dynamic searchable symmetric encryption(DSSE) combines dynamic update with searchable encryption, allowing users to not only achieve keyword retrieval, but also dynamically update encrypted data stored on semi-trusted cloud server, effectively protecting user's privacy. However, the majority of existing DSSE schemes exhibit inefficiencies in practical applications because of their complex structure. In addition, to store the status of keywords, the storage requirements of the client increase proportionally with the number of keyword/document pairs. Therefore, the client storage will be overwhelmed when confronted with a substantial increase in the volume of keyword/document pairs. To solve these issues, we propose a practical efficient dynamic searchable symmetric encryption scheme with lightweight clients—CoD-DSSE. A novel index structure similar to a chest of drawers is proposed in CoD-DSSE, which allows users to efficiently search all document indexes through XOR operations and keeps the keyword status on the server to lightweight clients. Furthermore, we use a random number generator to construct new search tokens for forward security and achieve backward security by using a Bloom filter to store the deleted document index, which can significantly reduce communication costs. The experimental and security analyses show that CoD-DSSE is efficient and secure in practice. [ABSTRACT FROM AUTHOR]