A common approach to protecting data confidentiality again-st potential adversaries is to encrypt the databases. Nevertheless, it is infeasible to perform meaningful computations on a ciphertext. Trusted Execution Environments (TEEs) offer a promising alternative by enabling computations on plaintext within a secure enclave, thereby supporting rich and complex queries. However, existing works either fall short in providing strong oblivious guarantees, fail to support queries such as non-equi joins, or suffer from significant efficiency bottlenecks. In this paper, we first address the oblivious order counting and encoding problem in a parallelized manner, enabling the counting and encoding of elements that satisfy a given order within an unordered sequence. Building on this, we propose parallelizable non-equi join algorithms for both single condition and multiple conditions. The experimental results show that our scheme completes a non-equi-join with a single condition, producing 16,000,000 output records in 26.4 s, and a multiple conditions non-equi-join producing 26,366,724 output records in 19.4 s, achieving up to 4.7 × and 2.04 × speedups over the state-of-the-art scheme, respectively.

The rapid deployment of emerging networks, such as the Internet of Things and cloud computing, has generated massive amounts of data. Data streaming is significant among these various data types due to its widespread use in many critical applications, such as gene sequencing, network intrusion detection, and stock trading. On the other hand, the continuously increased size of data streaming makes it impractical to store and manage the data locally, especially for those resource-constrained devices. Outsourcing the data streaming to cloud servers provides an ideal solution to the above storage issue. However, this raises the problem of how to guarantee the integrity of the outsourced data, as cloud servers may maliciously modify the data. To this end, the primitive of verifiable data streaming (VDS) was introduced to preserve the integrity of the outsourced data streaming, enabling data users to ensure that queried data items, including the contents and corresponding positions, are correct. Despite many proposed VDS protocols, most can only use the position index to query outsourced data streaming. Consequently, they fail to fulfill the requirements of those practical applications that need keyword queries. For example, in the setting of network intrusion detection, the data analyst would like to query all access records from the same IP address. In this paper, we extend the original VDS protocol to support keyword queries, i.e., allowing data users to retrieve outsourced data items with particular keywords. Specifically, we use a prefix tree to maintain keywords and another chameleon authentication tree to store data items. The two trees are bound together with cryptographic query proofs, ensuring the consistency between the position index and keyword queries. The proposed VDS protocol, which supports keyword queries, is proven secure in the standard model and outperforms previous VDS protocols in terms of functionality. The experimental results indicate that our proposal is also efficient and practical.

Data capsule provides a feasible solution for controllable data sharing, where data owners outsource their data capsules containing encrypted data and compliance-checking policies to the cloud server, and only valid users can run a compliant analysis program to process the decrypted data capsules in the Trusted Execution Environment (TEE), without obtaining the raw data. However, existing schemes cannot achieve verifiable accesses and updates, which means that malicious servers may use corrupted/old data capsules to deceive users and TEE. In this paper, we introduce the concept of Verifiable Data Capsule (VDC) for secure and controllable data sharing. Specifically, we first design a lightweight authentication tag, dubbed Locally Verifiable Chameleon Tag (LVCT), which allows the data owner to bind all data capsules to a constant-size tag and enables users to recover the local tags for validating data capsules. On this basis, we present a concrete VDC scheme that utilizes a dual-level authentication structure to realize verifiable data updates, and verifiable state updates triggered by regular access without the aid of the data owner. Furthermore, we propose an efficient trust evaluation protocol to judge the credibility of cloud servers. Finally, both security analysis and performance evaluation demonstrate the practicability of the proposed scheme.

As a promising decentralized paradigm, the verifiable and redactable blockchain offers a feasible solution for achieving authorized and controlled redaction of on-chain data. However, existing schemes suffer from rapidly expanding ledgers caused by authentication data structures and fail to strike a balance between permission supervision and redaction efficiency. In this paper, we propose a novel verifiable and redactable blockchain scheme that introduces a dual-level authentication architecture to achieve lightweight storage and permission supervision. To this end, we first design a dual-level authentication data structure that appends all blocks to a constant-size global tag, while supporting verifiable redaction and query over on-chain data. Likewise, we introduce a dual-level chameleon hash structure, which not only employs committee members holding sub-keys to redact on-chain data but also enables the certificate authority to use the master key to correct malicious redactions executed by corrupted committee members. Furthermore, we propose an efficient auditing protocol to enhance the integrity and consistency of the blockchain ledger during the process of synchronous circulation. Finally, both security analysis and performance evaluation prove that the proposed scheme is practical.

Blockchain technology, successful in cryptocurrency, holds transformative potential for various industries. In decentralized applications driven by blockchain, acquiring non-digitally verifiable data is crucial, particularly in smart contracts. To facilitate the transfer of off-chain data from websites to the blockchain, several studies have proposed various centralized and decentralized blockchain Oracles. However, centralized Oracles reintroduce central risks, such as the Single Point of Failure, while decentralized Oracles consistently rely on a voting mechanism, which incurs additional vulnerabilities and substantial costs. In this work, we uncover a misdirection attack in decentralized Oracles, resulting in a diminished security region in blockchain consensus. This manifests as prolonged settle times and reduced upper bounds for tolerance of adversarial consensus chip. By formalizing the voting process as a discrete-time Markov chain (DTMC), we further demonstrate that the maximum stake of the adversary for launching a misdirection attack is less than 50%. To counteract this threat, we introduce a novel voting model that relies on chain length rather than block data for voting. Formally, we propose the definition of our model named VoteFork. Following this, we present the specific consensus-based blockchain Oracle protocol, PSCBO. This protocol involves blockchain clients collecting and providing Oracle data, with an epoch-based voting mechanism to verify each set of Oracle information. We also analyze the security of the PSCBO backbone VoteFork, demonstrating its security region akin to a typical blockchain. Finally, we implement a proof-of-concept system to validate the security region and further underscore the practicality. Both security analysis and experiments affirm that PSCBO exhibits a higher adversarial fault tolerance and shorter waiting time to confirm transactions.

With the growing popularity of various Internet of Things (IoT) applications, securing data transmission over these networks become critical. The authenticated key exchange (AKE) protocol is a fundamental cryptographic primitive that achieves this goal by creating a shared session key. However, since IoT end devices are usually resource-constrained, devising secure and efficient AKE protocols for IoT applications remains challenging. In this paper, we investigate the design of zero round-trip time (0-RTT) session resumption protocols based on pre-shared keys, which enables an end device to send encrypted data to a server without prior key exchange. Specifically, we first propose a new construction of puncturable pseudo-random function (PRF), and prove its security under the RSA assumption. Then, based on the proposed puncturable PRF and authenticated encryption with associated data, we put forward a new construction of 0-RTT session resumption protocol that simultaneously provides forward security and resistance against replay attacks. We further demonstrate how to combine the proposed 0-RTT session resumption protocol with other symmetric AKE protocols for IoT applications. Both theoretical comparisons and experimental results indicate that our proposal has significant advantages in terms of computation and storage costs for practical parameter settings. Thus, it is especially desirable for constrained devices.

Limited by the local storage resource, data users have to encrypt their data and outsource the encrypted databases to cloud servers to enjoy low-cost, professional data management services, which promotes the rapid development of outsourcing database technology. Despite this, the complex underlying setting and loosely coupled database architecture lead to various security risks and performance bottlenecks, while there is currently no work to achieve a comprehensive evaluation of existing encrypted database solutions from the aspects of underlying settings, security levels, functions, etc. In this work, we first propose an evaluation model to assess SQL functionalities and security from multiple dimensions. Secondly, we categorise the existing SQL query schemes into three categories: software-based construction, hardware-based construction, and hybrid-based construction, that is, a combination of software and hardware components. On this basis, we analyse the framework, advantages, and limitations of classic and state-of-the-art schemes. Finally, we summarise the software-based and hardware-based approaches from dimensions of SQL functionality, security, and efficiency, thus clarifying their ideal application scenarios. Notably, SQL query schemes that exhibit minimal equality of pair leakage and support strong obliviousness can achieve higher levels of security. In addition, hardware-based solutions can achieve more complex SQL queries and superior performance without designing complex and functionally-limited cryptographic tools.

The rapid development of both hardware and software has promoted the popularization of various real-time applications like health monitoring and intrusion detection that are widely deployed in outsourcing scenarios, e.g., mobile edge computing and cloud computing. In these applications, end devices continuously generate unbounded sequences of data items at a fast rate, i.e., the so-called streaming data. Nevertheless, storing and processing massive amounts of streaming data poses a challenge for resources-restricted end devices. Although outsourcing data items to edge servers or cloud servers is an attractive solution to the above problem, it also brings a new challenge, i.e., how to guarantee the integrity of outsourced data, since streaming data applications are usually sensitive of both location and the corresponding context, and servers are not completely trusted. To this end, the primitive of verifiable data streaming (VDS) protocol was introduced to maintain outsourced streaming data, while preserving its integrity. However, existing VDS constructions mainly use the structure of Merkle hash tree, and inherently have logarithmic costs. Consequently, they are infeasible for real-time applications that are delay sensitive and generate unpredictable size of streaming data. In this paper, we optimize previous VDS protocols from the aspects of communication overhead and computation cost. Specifically, we adopt a technical route different from Merkle hash tree, i.e, combining the digital signature with the cryptographic accumulator. In our construction, we employ Boneh-Lynn-Shacham (BLS) signature to guarantee the integrity of the context and position of each outsourced data item, and adopt an RSA accumulator to invalidate the old signature after the corresponding data item was updated. This immediately yields an optimal VDS construction that has constant costs even under concurrent queries, which is more desirable for those resource-limited mobile devices. In addition, the aggregability of BLS signature makes our VDS construction capable of data auditing, which enables the user to remotely verify the integrity of outsourced streaming data. We provide a formal security proof of the proposed VDS construction under well-studied complexity assumptions in the random oracle model. As a proof-of-concept, we also implement our proposal, and conduct extensive experiments to demonstrate its practicability.

The primitive of verifiable data streaming (VDS) provides a secure data outsourcing solution for resource-constrained users, that is, they can stream their continuously-generated data items to untrusted servers while enabling publicly verifiable query and update. However, existing VDS schemes either require the server to store the authentication tags of all data items to support data query and auditing, or bind all data items into a constant-size tag to achieve optimal storage on the server side, but cannot achieve public auditing. To close this gap, in this paper, we first design a novel authentication data structure, dubbed retrievable homomorphic verifiable tags (RHVTs), which allows users to aggregate the authentication tags of all data items into a constant-size tag, and enables them to retrieve the original tags from the aggregated tag when necessary. Based on this, we propose a compact verifiable and auditable data streaming (CVADS) scheme, which adopts a single-level authentication mechanism to achieve more efficient data append and update, as well as optimal storage and public auditing. For better robustness and performance, we introduce a nested dual-level authentication mechanism and propose a blockchain-based CVADS (BCVADS) scheme to achieve a distributed CVADS with self-auditing. Finally, we prove the security of our schemes in the random oracle model and demonstrate their practicality through a visual performance evaluation.

Multi-signature schemes have attracted considerable attention in recent years due to their popular applications in PoS blockchains. However, the use of general multi-signature schemes poses a critical threat to the security of PoS blockchains once signing keys get corrupted. That is, after an adversary obtains enough signing keys, it can break the immutable nature of PoS blockchains by forking the chain and modifying the history from some point in the past. Forward-secure multi-signature (FS-MS) schemes can overcome this issue by periodically updating signing keys. The only FS-MS construction currently available is Drijvers et al's Pixel, which builds on pairing groups and only achieves forward security at the time period level. In this work, we present new FS-MS constructions that either are free from pairing or capture forward security at the individual message level (i.e., fine-grained forward security). Our first construction Pixel+ works for a maximum number of time periods T. Pixel+ signatures consist of only one group element, and can be verified using two exponentiations. It is the first FS-MS from RSA assumption, and has 3.5x and 22.8x faster signing and verification than Pixel, respectively. Our second FS-MS construction Pixel++ is a pairing-based one. It immediately revokes the signing key's capacity of re-signing the message after creating a signature on this message, rather than at the end of the current time period. Thus, it provides more practical forward security than Pixel. On the other hand, Pixel++ is almost as efficient as Pixel in terms of signing and verification. Both Pixel+ and Pixel++ allow for non-interactive aggregation of signatures from independent signers and are proven to be secure in the random oracle model. In addition, they also support the aggregation of public keys, significantly reducing the storage overhead on PoS blockchains. We demonstrate how to integrate Pixel+ and Pixel++ into PoS blockchains. As a proof-of-concept, we provide implementations of Pixel+ and Pixel++, and conduct several representative experiments to show that Pixel+ and Pixel++ have good concrete efficiency and are practical.

Secure client-side deduplication enables cloud server to efficiently save storage space and communication bandwidth without compromising privacy. However, the potential duplicate-faking attack (DFA) may cause data users to lose their outsourced data. Existing solutions can either only detect DFA and fail to avoid data loss, or have high storage costs. In this paper, we propose a blockchain-based secure deduplication scheme against DFA in decentralised storage. Specifically, we firstly propose a client-side deduplication protocol, in which the server does not need to store additional metadata to check subsequent uploaders, who only need to encrypt the challenged partial blocks instead of the entire file. Besides, we design a battle mechanism based on smart contract to protect users from losing data. When an uploader detects a DFA, he can apply for a battle with the previous uploader to achieve an effective punishment. Finally, security and performance analysis indicate the practicality of the proposed scheme.

Driven by various legal obligations and service requirements, the redactable blockchain was introduced to balance the modifiability and immutability of blockchain technology. However, such a blockchain inevitably generates one or even more acceptable versions for the same block data, enabling malicious full nodes to deceive light/new nodes with old data and even disrupt the consistency of the blockchain ledger. In this paper, we introduce the concept of verifiable redactable blockchain (VRBC) to provide efficient validity verification for on-chain data. To this end, we design a novel authentication data structure, called blockchain authentication tree (BAT), which utilizes a chameleon hash function and aggregatable vector commitment to bind continuously-appended blocks. Based on this, we propose an efficient VRBC scheme supporting integrity auditing, which not only allows light nodes to query and validate on-chain data, but also enables new nodes to check the integrity of the blockchain ledger before synchronizing it, effectively avoiding resource waste and security risks caused by invalid queries and ledger synchronization. Furthermore, we introduce some optimized strategies to improve the performance of the proposed scheme and extend it to transaction-level and permissionless VRBC, respectively. Finally, we demonstrate the practicability of the proposed scheme through detailed security analysis and visual performance evaluation.

With the prevalence of distributed network storage services, the security and dynamicity of cloud storage data have become essential focuses of attention. Meanwhile, research on secure deduplication, integrity audit, and dynamic operations has been extensively conducted. However, in existing research, many data deduplication schemes supporting auditing focus on static file storage. This paper proposes a blockchain-based dynamic data deduplication scheme that supports public auditing, enabling data’s dynamic operations. In addition, the existing proof of ownership is designed only to meet the needs of the server. Therefore, we adopt BLS short signature to design a secure and efficient bidirectional proof of ownership mechanism, supporting the server and client to prove they have the same data. Based on this, we design a multi-server storage mechanism under the supervision of blockchain, which achieves public auditing without a trusted third party and supports block-level deduplication within a server and file-level deduplication across servers. Finally, we demonstrate the feasibility and performance of the proposed scheme through experimental analysis.

The collaborative intrusion detection technique is an effective solution to protect users from various cyber-attacks, among which the large-scale trusted sharing and real-time updating of attack instances are the main challenges. However, the existing collaborative intrusion detection systems (CIDS) either can only achieve real-time instance sharing in a centralised setting or implement large-scale instance sharing through blockchain. In this paper, we propose a novel blockchain-based CIDS scheme. Specifically, we present a reputation-based consensus protocol, which incentivises service providers (SP) to evaluate the attack instances collected from collectors and punishes the malicious evaluators. Then, only trusted attack instances will be published on the blockchain to provide large-scale trusted intrusion detection services. Furthermore, we introduce a redactable blockchain technique to achieve dynamic instances update, which enables our scheme to provide a real-time intrusion detection service. Finally, we demonstrate the practicality of the proposed scheme through security analysis, theoretical analysis and performance evaluation.

As a main component of blockchain technology, smart contracts support multiple functions and hold large amounts of assets, which makes them a target for attackers. Statistics show that attacks on smart contracts account for three-quarters of all attacks on the blockchain applications, causing huge economic losses to users of smart contracts. The existing research mainly focuses on vulnerability detection of contracts that cannot achieve real-time protection of deployed contracts. In this paper, we propose a practical detection and defense scheme against smart contract attacks. Specifically, We use an attack detection method based on transaction features to detect attacks using miner nodes and use the attack detection results as a consensus to block the executions of attacks and achieve real-time defense against attacks. Theoretical analysis and simulation results show that our scheme only requires a small increase in storage and computational overhead to achieve effective defense against smart contract attacks.

Consensus mechanism, as the soul-building-block of decentralized settings, enables a series of blockchain applications, such as Bitcoin and Ethereum. For better security and soundness, more and more blockchain systems tend to adopt proof-of-authority (PoA) to avoid or alleviate the various security risks caused by their peer-to-peer (P2P) networks. However, the PoA protocol is also vulnerable to cloning attack (CA), which provides a potential pathway for double-spending attack and has not been well solved. In this paper, we propose a heartbeat-based defense scheme to achieve an effective CA detection in PoA blockchians. To this end, we first analyze two PoA algorithms, Aura and Clique, along with their CA. On this basis, we propose a heartbeat-based defense scheme that can detect CA effectively regardless of the underlying consensus algorithm of the blockchain. Then, to avoid the potential efficiency reduction caused by the increase of sealers, we further design an enhanced hierarchical node selection algorithm, in which sealers can challenge partial nodes selected randomly according our strategy to detect CA in an efficient manner. Finally, we theoretically estimate the precision rate model of our scheme and then establish a prototype PoA blockchain system to test the performance of our scheme. As expected, the experiment results are consistent with our theoretical analysis, which powerfully demonstrates the efficiency and practicability of the proposed scheme.

Secure deduplication and data auditing are significant in improving the resource utilization and data integrity protection of data outsourcing services. However, existing audit-enabled deduplication schemes cannot implement block-level deduplication over audit tags since they contain file information, and have to bear the consequent storage burden. Also, they suffer from the low coupling problem caused by the difference in optimal data chunking between deduplication and auditing. In this paper, we propose a blockchain-based compact audit-enabled deduplication scheme in decentralized storage. Specifically, we introduce the concept of N-ary tag commitment tree (NTCT), which integrates the information of all data blocks into a file authenticator to support integrity verification and enable block-level deduplication over audit tags. On this basis, we propose a blockchain-based compact audit-enabled deduplication protocol, which adopts an aggregatable vector commitment to generate audit tags, thereby overcoming the low coupling problem between deduplication and auditing. Notably, data users can outsource the task of tag generation to storage servers. Meanwhile, the capabilities of duplication detection, proof of ownership (PoW), and integrity verification are integrated into audit tags to reduce tag redundancy. Furthermore, we present an update protocol to allow data users to achieve a lightweight data update without uploading the entire new data. Finally, security analysis and performance evaluation demonstrate that our scheme is practical.

Data owners outsource their data to remote storage providers without keeping local replicas to save their precious storage resources. However, the ownership and management of data are separated after outsourcing. How to ensure the integrity and recoverability of outsourced data becomes a significant problem. Provable Data Possession (PDP) and Proofs of Retrievability (POR) are two cryptographic protocols that enable users to verify the integrity of outsourced data. Nevertheless, the state-of-the-art PDP and POR schemes either need users to perform the complicated audit tasks by themselves or delegate these tasks to a Third-Party Auditor (TPA). Moreover, these schemes are constructed on a centralized storage framework which vulnerably suffers single-point-of-failure. In this paper, we propose a blockchain-based decentralized self-auditing scheme with batch verification. Firstly, data owners outsource their data to decentralized storage nodes, which can achieve self-auditing based on blockchain without TPA. Secondly, our scheme uses Pedersen-based polynomial commitment to significantly reduce the number of authenticators. Furthermore, we propose a batch verification algorithm, which can verify multiple proofs from different storage nodes to improve the verification efficiency. Finally, we analyze the security of our scheme and implement a gas-efficient system prototype using the smart contracts of the Ethereum Reposten test network. The results demonstrate that the scheme is practical.

Data deduplication and public auditing are significant for providing secure and efficient network storage services. However, the existing data deduplication schemes supporting auditing not only cannot effectively alleviate the threats of the single point of failure and duplicate-faking attack, but also have to bear the massive waste of computation and storage resources caused by metadata redundancy and repetitive audit tasks. In this article, we propose a blockchain-based secure deduplication and shared auditing scheme in decentralized storage. Specifically, our scheme utilizes a novel deduplication protocol based on the double-server storage model to achieve efficient space-saving while protecting data users from losing data under a single point of failure and duplicate-faking attack. Besides, it sharply reduces the computation and storage costs of metadata by introducing a lightweight authenticator generation algorithm and update protocol. On this basis, our scheme further adopts a blockchain-based two-way shared auditing mechanism to achieve decentralized public auditing without the third-party auditor, in which the audit authenticators and results of outsourced data are shared among its users to avoid repetitive audit tasks. Security and performance analysis indicates the practicability of our scheme.

In cloud storage, public auditing is a more popular data integrity verification technique since it allows users to delegate auditing tasks to a fully trusted third-party auditor (TPA). However, it is difficult to find such a TPA in practical application. Besides, the centralised auditing model makes TPA have to bear burdensome work pressure, which limits the practicability of existing schemes. In this paper, we firstly proposed a blockchain-based generalised shared auditing mechanism BCSA in the cross-user scenario, which aims at achieving available public auditing with a non-fully trusted TPA, and reducing the user's auditing fees and TPA's work pressure by allowing data users to share their auditing procedure with others. Furthermore, we initialise a concrete construction BCSAD with Diffie–Hellman protocol for the cross-user auditing scenario with different data. Likewise, we also propose a novel construction BCSAI for the cross-user auditing scenario with identical data, which utilises a password-authenticated key exchange (PAKE) protocol to achieve shared auditing and ciphertext deduplication, reducing data storage and auditing fees for data users and alleviating service pressure on the cloud server and TPA. Security and performance analysis evaluate the practicability of the proposed scheme.