Internet of things (IoT) devices generate a massive amount of data every second in our lives. While cloud storage brings convenience to the users, it has the disadvantages of low scalability and weak reliability. Blockchain-based distributed storage eliminates data loss due to the tamper-resistant characteristic. Nonetheless, blockchain storage raises some confidentiality and retrieval efficiency issues of data. Searchable Symmetric Encryption (SSE) is an effective search scheme based on ciphertexts, which ensures data security. However, with the increase of data on the blockchain, the data retrieval on the blockchain will be difficult. In this paper, a Complete Binary Tree Searchable Symmetric Encryption using Blockchain (KCB-BC-SSE) scheme is proposed. According to the number of searchers, the scheme is divided into single searcher and multiple searchers where the search efficiency is improved in theory. And the simulation on ethereum shows the feasibility of our scheme. The security analysis illustrates our scheme achieves security under the chosen keyword attack.
Matteo Loporchio, Anna Bernasconi, Damiano Di Francesco Maesa, Laura Ricci
In many blockchain networks, light nodes (e.g. mobile clients) with few computational resources must rely on more powerful full nodes to retrieve transactions from the chain. However, in this untrusted environment a malicious full node could deliver altered or incomplete information, requiring query authentication techniques to ensure the integrity of the results. To this aim, we study an authentication mechanism for spatial information (i.e. data representing the location, size, and shape of objects in a geographical coordinate system). We assume that light nodes issue range queries to obtain data from a single block. To enable authentication, we propose to construct a Merkle R-tree for each block and embed its root into the corresponding header, so that full nodes can exploit it to fetch information and construct a proof of integrity for lightweight clients. We also develop a new algorithm based on sorting and partitioning for constructing Merkle R-trees from a set of spatial transactions and employ space-filling curves to preserve the locality of elements. We examine its theoretical complexity, evaluate it experimentally on a real data set and compare it against other popular construction strategies. Results show that, as queries become more selective, trees generated with our solution improve query performance and reduce verification times with respect to other approaches. Moreover, we observe that the overhead induced by the tree construction is negligible if compared to the average inter-block time of popular blockchain protocols such as Bitcoin and Ethereum.
Privacy protection and open sharing are the core of data governance in the AI‐driven era. A common data‐sharing management platform is indispensable in the existing data‐sharing solutions, and users upload their data to the cloud server for storage and dissemination. However, from the moment users upload the data to the server, they will lose absolute ownership of their data, and security and privacy will become a critical issue. Although data encryption and access control are considered up‐and‐coming technologies in protecting personal data security on the cloud server, they alleviate this problem to a certain extent. However, it still depends too much on a third‐party organization’s credibility, the Cloud Service Provider (CSP). In this paper, we combined blockchain, ciphertext‐policy attribute‐based encryption (CP‐ABE), and InterPlanetary File System (IPFS) to address this problem to propose a blockchain‐based security sharing scheme for personal data named BSSPD. In this user‐centric scheme, the data owner encrypts the sharing data and stores it on IPFS, which maximizes the scheme’s decentralization. The address and the decryption key of the shared data will be encrypted with CP‐ABE according to the specific access policy, and the data owner uses blockchain to publish his data‐related information and distribute keys for data users. Only the data user whose attributes meet the access policy can download and decrypt the data. The data owner has fine‐grained access control over his data, and BSSPD supports an attribute‐level revocation of a specific data user without affecting others. To further protect the data user’s privacy, the ciphertext keyword search is used when retrieving data. We analyzed the security of the BBSPD and simulated our scheme on the EOS blockchain, which proved that our scheme is feasible. Meanwhile, we provided a thorough analysis of the storage and computing overhead, which proved that BSSPD has a good performance.
It has become a truism that the speed of technological progress leaves law and policy scrambling to keep up. But in addition to creating new challenges, technological advances also enable new improvements to issues at the intersection of law and technology. In this thesis, I develop new cryptographic tools for informing and improving our law and policy, including specific technical innovations and analysis of the limits of possible interventions. First, I present a cryptographic analysis of a legal question concerning the limits of the Fifth Amendment: can courts legally compel people to decrypt their devices? Our cryptographic analysis is useful not only for answering this specific question about encrypted devices, but also for analyzing questions about the wider legal doctrine. The second part of this thesis turns to algorithmic fairness. With the rise of automated decision-making, greater attention has been paid to statistical notions of fairness and equity. In this part of the work, I demonstrate technical limits of those notions and examine a relaxation of those notions; these analyses should inform legal or policy interventions. Finally, the third section of this thesis describes several methods for improving zero-knowledge proofs of knowledge, which allow a prover to convince a verifier of some property without revealing anything beyond the fact of the prover's knowledge. The methods in this work yield a concrete proof size reduction of two plausibly post-quantum styles of proof with transparent setup that can be made non-interactive via the Fiat-Shamir transform: "MPC-in-the-head," which is a linear-size proof that is fast, low-memory, and has few assumptions, and "Ligero," a sublinear-size proof achieving a balance between proof size and prover runtime. We will describe areas where zero-knowledge proofs in general can provide new, currently-untapped functionalities for resolving legal disputes, proving adherence to a policy, executing contracts, and enabling the sale of information without giving it away.
Open access
Cryptography and Data Security
Digital and Cyber Forensics
Physical Unclonable Functions (PUFs) and Hardware Security
The classic Elliptic curve digital Signature Algorithm (ECDSA) uses one inversion operation in the process of signature and verification, which greatly reduces the efficiency of digital signatures. Up to now, most research schemes improve efficiency by reducing reverse operations, but they fail to attach importance to such issues as forgery signature attack. At the same time, in the blockchain, the weak randomness of ECDSA will lead to the attack of forging random numbers, which is a potential problem of digital currency transactions. In consideration of this reason, in this article, an improved provably secure elliptic curve digital signature scheme is constructed. First, the new scheme introduces double parameters in the signature process, that can effectively resist the weak randomness attack of ECDSA in Bitcoin, and can be applied to blockchain digital currency trading systems. Second, in the random oracle model, it is provably indistinguishable against Elliptic Curve Discrete Logarithm Problem (ECDLP) under the super type I and type II adversary. Third, the new scheme avoids the inverse operation in the signature and verification phase. Compared with the ECDSA, the running speed is optimized by 50.1%. Similarly, the proposed scheme has higher computational efficiency than other existing algorithms.
After its debut with Bitcoin in 2009, Blockchain has attracted enormous attention and been used in many different applications as a trusted black box. Many applications focus on exploiting the Blockchain-native features (e.g. trust from consensus, and smart contracts) while paying less attention to the application-specific requirements. In this paper, we initiate a systematic study on the applications in the education and training sector, where Blockchain is leveraged to combat diploma fraud. We first present a general system structure for digitized diploma management systems and identify both functional and non-functional requirements. We then show that all existing Blockchain-based systems fall short in meeting these requirements. Inspired by the analysis, we propose a Blockchain-facilitated solution by leveraging some basic cryptographic primitives and data structures. Our analysis shows that the proposed solution respects all the identified requirements by design and can be further extended to enhance its security and privacy guarantees. Finally, we investigate the proposed solution’s computational complexity and demonstrate its practicality.
Open access
Blockchain Technology Applications and Security
Cryptography and Data Security
Advanced Steganography and Watermarking Techniques
The Notarial Office(NO), working on providing various essential certificates, still relies on manual handling and requires paper materials from other government departments. That brings lots of inconvenience. The Notarial Office rejects non-local paper materials for their lower credibility in the local place and then cannot provide cross-borders services. It also easily cause sensitive information leakage as copies of paper materials have been stored. In this case, a blockchain-based system is suitable to address challenges in this scenario because of its advantages (e.g, decentralized, immutability, transparency, auditability). We implemented this system on top of the Hyperledger Fabric. Moreover, we replace manual operations with smart contracts, set extra ledgers to off-load different types of transactions and provide encryption for private information when needed. In the end, we get an expected result. That is, the modification outperformed the unmodified network in experiments.
Santeri Paavolainen, Christopher Carr, Essam Ghadafi
The Ethereum blockchain is one of the most popular permissionless blockchains. A consequence of its popularity has been the growth of processing and data storage requirements for any node participating in the Ethereum blockchain network. For constrained devices such requirements are often infeasible to meet. To cater for such nodes, a so-called light protocol has been proposed for Ethereum where the responsibility of maintaining a correct state representation is delegated to light protocol servers. Previous research has identified dependence on external state management as a potential security vulnerability that exclusively impacts light nodes. Although a simple mitigation strategy is available, it comes at the expense of increased latency. In this work, we propose a new Ethereum node type, which we call a subset node, as an extension of the light protocol. Our proposal allows subset nodes to gain a lower latency than a pure light node with comparable or even higher security assurances by tracking and evaluating only a subset of all of the transactions issued on the blockchain. We provide a formal proof on the correctness of the blockchain state used by the subset node under the proposed model. To evaluate the practical feasibility of the subset node model, we analyze one year of historical transaction data from Ethereum, and demonstrate that a subset node tracking the state of a single account can achieve a significant reduction in storage and computational requirements when compared to a full node.
Bong Gon Kim, Young-Seob Cho, Seok-Hyun Kim, Hyoungshick Kim · 5 authors
Decentralized identifiers (DID) has shown great potential for sharing user identities across different domains and services without compromising user privacy. DID is designed to enable the minimum disclosure of the proof from a user's credentials on a need-to-know basis with a contextualized delegation. At first glance, DID appears to be well-suited for this purpose. However, the overall security of DID has not been thoroughly examined. In this paper, we systemically explore key components of DID systems and analyze their possible vulnerabilities when deployed. First, we analyze the data flow between DID system components and analyze possible security threats. Next, we carefully identify potential security threats over seven different DID functional domains, ranging from user wallet to universal resolver. Lastly, we discuss the possible countermeasures against the security threats we identified.
This paper considers the problem of expanding a language class that can be proven by a non-interactive zero-knowledge proof system (NIZK) in a black-box manner in the common reference string model. Namely, given NIZKs for two languages,L0andL1, can we construct an NIZK forL0vL1in a black-box manner? NIZKs for disjunctive languages have a large number of applications, such as electronic voting. Therefore, such a black-box construction may enable the efficient constructions of such applications. However, Abe et al. (PKC 2020) showed that this is impossible if the two given NIZKs are simulation-sound. In this paper, we prove that it is also impossible if the two given NIZKs are constructed by the commit-and-prove methodology that is typically used in many cryptographic protocols, including NIZKs. This result suggests that if we want to augment the capability of NIZKs in terms of the languages they can prove, we should rely on certain properties or structures of the underlying NIZKs, such as algebraic structures.
Abstract With the promotion of “Internet +” and smart cities, as an important data voucher, electronic certificate brings great convenience to people’s life. However, the phenomenon of “data island” based on the electronic certificate database of each city hinders the sharing of an electronic certificate. In addition, problems such as centralization of data storage, poor security, and tamper-proof modification are common in electronic certificate libraries. To solve these problems, we present a blockchain-based electronic certificate sharing scheme, which uses the InterPlanetary File System (IPFS) and Ethereum smart contract to achieve secure storage and data sharing of electronic certificate by taking advantage of the non-tampering and decentralization of blockchain. At the same time, we achieve fine-grained access control by using attribute-based encryption of ciphertext policy and assigning attribute keys to users without affecting retrieval efficiency. Finally, through the simulation and performance analysis of the Ethereum test network, the analysis results show that our scheme is effective and feasible.
Abstract It is well known that several cryptographic primitives cannot be achieved without a common reference string (CRS). Those include, for instance, non-interactive zero-knowledge for NP, or maliciously secure computation in fewer than four rounds. The security of those primitives heavily relies on the assumption that the trusted authority, who generates the CRS, does not misuse the randomness used in the CRS generation. However, we argue that there is no such thing as an unconditionally trusted authority and every authority must be held accountable for any trust to be well-founded. Indeed, a malicious authority can, for instance, recover private inputs of honest parties given transcripts of the protocols executed with respect to the CRS it has generated. While eliminating trust in the trusted authority may not be entirely feasible, can we at least move towards achieving some notion of accountability? We propose a new notion in which, if the CRS authority releases the private inputs of protocol executions to others, we can then provide a publicly-verifiable proof that certifies that the authority misbehaved. We study the feasibility of this notion in the context of non-interactive zero knowledge and two-round secure two-party computation.
Karim Baghery, Cyprien Delpech de Saint Guilhem, Emmanuela Orsini, Nigel P. Smart · 5 authors
This paper introduces M-Circuits, a program representation which generalizes arithmetic and binary circuits. This new representation is motivated by the way modern multi-party computation (MPC) systems based on linear secret sharing schemes actually operate. We then show how this representation also allows one to construct zero knowledge proof (ZKP) systems based on the MPC-in-the-head paradigm. The use of the M-Circuit program abstraction then allows for a number of program-specific optimizations to be applied generically. It also allows to separate complexity and security optimizations for program compilation from those for application protocols (MPC or ZKP).
Carmit Hazay, Muthuramakrishnan Venkitasubramaniam, Mor Weiss
Zero-Knowledge PCPs (ZK-PCPs; Kilian, Petrank, and Tardos, STOC `97) are PCPs with the additional zero-knowledge guarantee that the view of any (possibly malicious) verifier making a bounded number of queries to the proof can be efficiently simulated up to a small statistical distance. Similarly, ZK-PCPs of Proximity (ZK-PCPPs; Ishai and Weiss, TCC `14) are PCPPs in which the view of an adversarial verifier can be efficiently simulated with few queries to the input. Previous ZK-PCP constructions obtained an exponential gap between the query complexity q of the honest verifier, and the bound q^* on the queries of a malicious verifier (i.e., q = poly log (q^*)), but required either exponential-time simulation, or adaptive honest verification. This should be contrasted with standard PCPs, that can be verified non-adaptively (i.e., with a single round of queries to the proof). The problem of constructing such ZK-PCPs, even when q^* = q, has remained open since they were first introduced more than 2 decades ago. This question is also open for ZK-PCPPs, for which no construction with non-adaptive honest verification is known (not even with exponential-time simulation). We resolve this question by constructing the first ZK-PCPs and ZK-PCPPs which simultaneously achieve efficient zero-knowledge simulation and non-adaptive honest verification. Our schemes have a square-root query gap, namely q^*/q = O(√n) where n is the input length. Our constructions combine the "MPC-in-the-head" technique (Ishai et al., STOC `07) with leakage-resilient secret sharing. Specifically, we use the MPC-in-the-head technique to construct a ZK-PCP variant over a large alphabet, then employ leakage-resilient secret sharing to design a new alphabet reduction for ZK-PCPs which preserves zero-knowledge.
The features of decentralization and tamper-proof enable blockchain to be an emerging technology for integrity protection of important data stored on it. Blockchains are also used to combine with cloud storage for access control and sharing of private data. To protect the confidentiality of the private data, attribute-based encryption (ABE) schemes that can provide one-to-many encryption are commonly used as the solutions. However, there are problems, such as inefficiency, key abuse, and inflexibility of access control policy, when adopting ABE solutions. This paper proposes an efficient traceable attribute-based encryption with dynamic access control (TABE-DAC) scheme based on blockchain for fine-grained sharing of encrypted private data on cloud. The proposed TABE-DAC scheme supports traceability for the accountability of malicious users who leak the private key. The proposed solution also realizes dynamic access control where data owners have the flexibility to update access control policy. We also prove the security of the proposed TABE-DAC scheme. Finally, through theoretical comparison and experimental analysis, we verify the efficiency of the proposed solution.
Cloud computing has now become a very standardised concept in our society. However, many modern applications need a better level of security that includes saving data from internal breaches. Thus, cloud databases need effective security mechanisms to keep track of data modifications. This paper will introduce the enhanced structure of cloud relational database (RDB) based on blockchain technology (BC) named BC over cloud-RDB. To provide the client with an effective self-verification process to detect and prevent erroneous manipulation of RDBs. We proposed two systems to improve cloud-RDB: agile BC-based RDB and secure BC-based RDB. Both are distributed among several cloud service providers based on the Byzantine Fault Tolerance consensus. Additionally, both rely on linking records to each other using the SHA-256. At the same time, secure BC-based RDB uses a proof-of-work consensus to make data offensive operation impossible. Based on both systems’ performance and security analysis, the agile BC-based RDB is highly suggested for the high throughput database. On the other hand, the secure BC-based RDB is recommended for RDB that contains sensitive data and low throughput performance. The improved RDB is flexible and can be operated based on the data owner’s specifications.