Using existing resources to create teaching materials can save effort and achieve the desired quality easily. Yet while some resources can be used freely for educational purposes, others such as textbooks or online course materials cannot. This is a particular problem during a pandemic when much teaching has gone online and the risk of teachers violating copyright is even higher. Therefore, a solution that facilitates the usage of copyright-restricted resources for generating teaching materials with royalty sharing is needed. Our work exploits the advantage of blockchain technology and proposes a system to bond participants with a smart contract; it securely registers records of multiple authorships and contribution distribution of a teaching material that reuses in part, existing resources. Such records can be used as authorship evidence to claim economic benefits when a material is used. We implement TMchain on Ethereum-Remix IDE with a core smart contract. To lower the cost of using blockchain, the material files are stored off-chain and tied to the word processing system for the final authorship and contribution share determination when a material is completed. Furthermore, we test TMchain with teaching material creation scenarios to demonstrate its effective and practical potential.
While distributed databases offer great promise their decentralized nature poses a number of security and privacy issues. In what ways can parties misbehave? If a database is truly distributed can a malicious actor hide their misdeeds by presenting conflicting views of the database? Can we overcome such deceit and either prevent it by eliminating trust assumptions or detect such perfidy and hold the malicious party to account? We study these questions across two distributed databases: RPKI (Resource Public Key Infrastructure), which is used to authenticate the allocation and announcement of IP prefixes; and Bitcoin, a cryptocurrency that utilizes a permissionless database called a blockchain to track the transfer and ownership of bitcoins. The first part of this dissertation focuses on RPKI and the potential of RPKI authorities to misbehave. We consider the methods, motivations, and impact of this misbehavior and how an RPKI authority can present inconsistent views to hide this misbehavior. After studying the problem we propose solutions to detect and identify such misbehavior. Now we turn our attention to Bitcoin. We look at ways an attacker can manipulate Bitcoin's Peer-to-Peer network to cause members of the network to have inconsistent views of Bitcoin's blockchain and subvert Bitcoin's core security guarantees. We then propose countermeasures to harden Bitcoin against such attacks. The final part of this dissertation discusses the problem of privacy in Bitcoin. Many of the protocols developed to address Bitcoin's privacy limitations introduce trusted parties. We instead design privacy enhancing protocols that use an untrusted intermediary to mix \aka anonymize, bitcoin transactions via blind signatures. To do this we must invent a novel blind signature fair-exchange protocol that runs on Bitcoin's blockchain. This dissertation favors a dirty slate design process. We work to layer protections on existing protocols and when we must make changes to the underlying protocol we carefully weigh compatibility and deployment considerations. This philosophy has resulted in some of the research described in this dissertation influencing the design of deployed protocols. In the case of Bitcoin our research is currently used to harden a network controlling approximately a trillion dollars.
With the development of electronic systems, ideas have repeatedly arisen to create an electronic analogue of cash for remote payment. Cryptocurrency technology was originally aimed at the absence of a trusted node - one whose actions are guaranteed to be true and who can confirm the correctness of other people's operations. For the first time, this problem was solved in the Bitcoin system due to the artificial complication of making changes to the transaction history register.
Adeeba Naaz, T. V. Pavan Kumar B, Maria Francis, Kotaro Kataoka
Authentication while maintaining anonymity when availing a service over the internet is a significant privacy challenge. Anonymous credentials (AC) address this by providing the user with a credential issued by a trusted entity that convinces the service provider (SP) that the user is authenticated but reveals no other information. The existing AC schemes assume a single trusted authority (certifier) that validates all the user attributes. In practice, however, a user may require different attributes to be attested by different certifiers. This means that the user has to get multiple credentials, increasing the burden on theSPwho has to verify each one of them. Moreover, complete anonymity can be misused. We propose adecentralized threshold revocable anonymous credential (DTRAC)scheme over blockchains that supports – a) attestation of attributes by multiple certifiers, and b) anonymity revocation through a set of distributed openers, by integrating threshold opening to the state-of-the-art threshold anonymous credential issuance scheme, Coconut [34]. DTRAC generates a single credential on attributes that are attested by multiple certifiers, freeing the SP from the hassle of verifying multiple credentials. We analyze the security of DTRAC formally in the universal composability (UC) framework. We also implement a prototype on Ethereum using smart contracts and give a detailed analysis of its performance.We compare the verification time for credentials with attributes attested by multiple certifiers in both DTRAC and Coconut and see that in terms of execution time and gas consumption, DTRAC performs significantly better than Coconut. It also scales better, with the performance gain of DTRAC over Coconut increasing linearly with the number of certifiers.
Zhonghao Yuan, Jiaojiao Wu, Jianpeng Gong, Yao Liu · 6 authors
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.
The cloud storage service provides the storage and access function for massive data, reducing the management cost for large amounts of data. The data integrity verification scheme in cloud storage can be employed to help users confirm the integrity of outsourced data. Although public data integrity verification schemes allow users to outsource data integrity verification to third-party auditor (TPA), there are still many problems with centralized TPA in terms of security and efficiency. In recent years, researchers have tried to apply blockchain technology to solve the centralization problem of traditional methods, but these schemes do not pay attention to the problem of efficiency degradation caused by the use of blockchain technology. This paper proposes an efficient data integrity verification scheme for multi-cloud storage services by using blockchain technology. The overall verification can verify the integrity of multiple CSPs, which solves the problems of low computational efficiency. Local verification can trace the source to the specific damaged CSP, which is more secure and reliable. In addition, this paper puts the data verification process directly in the blockchain for public execution and provides data integrity verification services without the assistance of any third-party audit platform, avoiding the security problems caused by untrusted TPA. Theoretical analysis and experiments verify the safety and effectiveness of the scheme.
Junaid Arshad, Muhammad Ajmal Azad, Alousseynou Prince, Jahid Ali · 5 authors
Reputation systems are an important means to facilitate trustworthy interactions between on-and off-chain services and users. However, contemporary reputation systems are typically dependent on a trusted central authority to preserve privacy of raters or on adding noise into the user feedback. Moreover, the accuracy of reputation values relies on the integrity of user feedback or input; this feedback should not be tampered with or misused for other purposes. This paper presents blockchain-based reputation system named REPUTABLE (A Decentralized Reputation System for blockchain-based Ecosystems), which computes the reputation of service providers and external services within a blockchain ecosystem through decentralized on-chain and off-chain implementation. Specifically, REPUTABLE not only ensures privacy, but also reliability, integrity and accuracy of reputation values, while incurring minimal overhead. It also enables performing certain data or statistical analytics functions on user feedback, whilst preserving security, privacy, accountability and unlinkability of participants and their feedback. We present a proof-of-concept implementation and a demonstration of the REPUTABLE system. Finally, by means of formal and empirical evaluation, we show the effectiveness of our proposed system to preserve the anonymity of user feedback and the high performance of its blockchain-based implementation.
Yongli Tang, Yuanhong Li, Qing Ye, Ying Li · 5 authors
Although the existing group signature schemes from lattice have been optimized for efficiency, the signing abilities of each member in the group are relatively single. It may not be suitable for complex applications. Inspired by the pioneering work of Bellare and Fuchsbauer, we present a primitive called policy-based group signature. In policy-based group signatures, group members can on behalf of the group to sign documents that meet their own policies, and the generated signatures will not leak the identity and policies of the signer. Moreover, the group administrator is allowed to reveal the identity of signer when a controversy occurs. Through the analysis of application scenarios, we concluded that the policy-based group signature needs to meet two essential security properties: simulatability and traceability. And we construct a scheme of policy-based group signature from lattice through techniques such as commitment, zero-knowledge proof, rejection sampling. The security of our scheme is proved to be reduced to the module short integer solution (MSIS) and module learning with errors (MLWE) hard assumptions. Furthermore, we make a performance comparison between our scheme and three lattice-based group signature schemes. The result shows that our scheme has more advantages in storage overhead and the sizes of key and signature are decreased roughly by 83.13%, 46.01%, respectively, compared with other schemes.
The electronic know your customer (e-KYC) is a system for the banking or identity provider to establish a customer identity data verification process between relying parties. Due to the efficient resource consumption and the high degree of accessibility and availability of cloud computing, most banks implement their e-KYC system on the cloud. Essentially, the security and privacy of e-KYC related documents stored in the cloud becomes the crucial issue. Existing e-KYC platforms generally rely on strong authentication and apply traditional encryption to support their security and privacy requirement. In this model, the KYC system owner encrypts the file with their host’s key and uploads it to the cloud. This method induces encryption dependency and communication and key management overheads. In this paper, we introduce a novel blockchain-based e-KYC scheme called e-KYC TrustBlock based on the public key encryption method binding with the client consent enforcement to deliver trust, security and privacy compliance. In addition, we introduce attribute-based encryption to enable the privacy preserving and fine-grained access of sensitive transactions stored in the blockchain. Finally, we conduct experiments to show that our system is efficient and scalable in practice.
This paper proposes a novel lattice-based aggregate signature (LAS) scheme that bring post-quantum security to the Bitcoin system without sacrificing its transaction efficiency. Bitcoin currently employs Elliptic Curve Digital Signature Algorithm (ECDSA), which is insecure against the emerging quantum technology, so post-quantum signature schemes like the proposed LAS will become necessary in the near future. However, most of the post-quantum signatures schemes have large signature sizes which decrease Bitcoin’s efficiency while our proposed scheme does not have this negative side effect. Our LAS scheme is based on CRYSTALS-Dilithium and a zero-knowledge Scalable Transparent Arguments of Knowledge (STARK) protocol. CRYSTALS-Dilithium is the most prominent algorithm chosen by the National Institute of Standards and Technology (NIST), yet it still has an adverse limitation: it would cause Bitcoin’s transaction efficiency to fall by 17 times due to its relatively large signature size. On the other hand, the proposed LAS scheme takes full advantage of signature aggregation using the STARK protocol and Dilithium’s easy and fast implementation, thus generating signatures with post-quantum security and small signature sizes which are critical to transaction efficiency. Our proofs convey the correctness, compactness, and post-quantum security of our construction in the quantum random oracle model, and our implementation conveyed that the proposed scheme would only decrease Bitcoin’s transaction efficiency by 3 times, a significant improvement from using Dilithium and other lattice-based aggregate signature schemes. Our proposed scheme has many advantages over the existing schemes and may become very valuable to Bitcoin.
Engin Zeydan, Jorge Baranda, Josep Mangues‐Bafalluy
Existing network service provisioning and lifecycle management (LCM) workflows rely on heterogeneous devices from multiple vendors and collaboration between multiple network actors, which can lead to numerous trust management and interoperability issues. Blockchain networks (BCNs) are a revolutionary way to establish trust in untrusted environments. In this complex environment, BCNs can help ensure transparency and security for network service LCM. However, BCNs are also vulnerable to quantum attacks. Advances in quantum computing will challenge the security of existing blockchain technology based on Public Key Infrastructure (PKI) technologies. In this paper, we explore how network services can be managed in a multiple administrative scenario. Our approach uses BCNs to track the operational steps of network service instantiation metrics while benefiting from the security features of post-quantum cryptography (PQC). Together with the use of N-th degree Truncated polynomial Ring Units (NTRU) as an example of a PQC algorithm that relies on the parallelization power of the Toom-Cook computation method with different security levels, we have shown that Quorum can provide a lower average time-to-write value compared to other BCNs considered (Ethereum and Hyperledger). At the end of the paper, we discuss the evaluation results and future directions regarding the coexistence of PQC algorithms and BCNs for network service orchestration and service federation between multiple administrative domains.