Blockchain Papers

Dimitris Karakostas, Aggelos Kiayias, Mario Larangeira

No abstract is available for this record.

Behnam Kiani Kalejahi, Ruslan Eminov, Aga Guliyev

Blockchain can mean many things to many people. It is a set of protocols and encryption technologies for securely storing data on a distributed network for the developers. It is a distributed ledger for business and finance and the technology underlying the explosion of new digital currencies. For technologists, it is the driving force behind the next generation of the internet. On the other hand, it is a transformational technology facilitating large-scale human progress in previously unimagined ways for the rest of the people, a tool for radically reshaping society and economy. Some view it as a disruptive technology that can be the source of a great deal of fraud, illegal activity, where others see opportunities to bring into existing systems by providing decentralization, transparency, and efficiency. This complex technological, economic, and social phenomenon has been the subject of fervent debate. It calls into question what might have been seen to be established parameters of the modern world like currency, economics, trust, value, and exchange. It is a revolutionary new computing paradigm and one of the most significant, fundamental digital platforms’ advances since the internet. It is an emergent technology experiencing very rapid evolution, and so is our understanding of what it is and what it can be. This paper is subject to the use of Blockchain concepts in mobile networks to strengthen the Home Location Registry (HLR) database and make it decentralized for secure transactions and in banking and financial centers. Blockchain also holds potential implications for global commerce. It could make trade more efficient by removing the manual and paper-based processes and introducing streamlined and automated processes.

Geoffroy Couteau, Michael Klooß, Huang Lin, Michael Reichle

No abstract is available for this record.

Benny Applebaum, Eyal Golombek

We study the randomness complexity of interactive proofs and zero-knowledge proofs. In particular, we ask whether it is possible to reduce the randomness complexity, R, of the verifier to be comparable with the number of bits, C_V, that the verifier sends during the interaction. We show that such randomness sparsification is possible in several settings. Specifically, unconditional sparsification can be obtained in the non-uniform setting (where the verifier is modelled as a circuit), and in the uniform setting where the parties have access to a (reusable) common-random-string (CRS). We further show that constant-round uniform protocols can be sparsified without a CRS under a plausible worst-case complexity-theoretic assumption that was used previously in the context of derandomization. All the above sparsification results preserve statistical-zero knowledge provided that this property holds against a cheating verifier. We further show that randomness sparsification can be applied to honest-verifier statistical zero-knowledge (HVSZK) proofs at the expense of increasing the communication from the prover by R-F bits, or, in the case of honest-verifier perfect zero-knowledge (HVPZK) by slowing down the simulation by a factor of 2^{R-F}. Here F is a new measure of accessible bit complexity of an HVZK proof system that ranges from 0 to R, where a maximal grade of R is achieved when zero-knowledge holds against a "semi-malicious" verifier that maliciously selects its random tape and then plays honestly. Consequently, we show that some classical HVSZK proof systems, like the one for the complete Statistical-Distance problem (Sahai and Vadhan, JACM 2003) admit randomness sparsification with no penalty. Along the way we introduce new notions of pseudorandomness against interactive proof systems, and study their relations to existing notions of pseudorandomness.

Ruba Awadallah, Azman Samsudin, Je Sen Teh, Mishal Almazrooie

Due to its wide accessibility, cloud services are susceptible to attacks. Data manipulation is a serious threat to data integrity which can occur in cloud computing - a relatively new offering under the umbrella of cloud services. Data can be tampered with, and malicious actors could use this to their advantage. Cloud computing clients in various application domains want to be assured that their data is accurate and trustworthy. On another spectrum, blockchain is a tamper-proof digital ledger that can be used alongside cloud technology to provide a tamper-proof cloud computing environment. This paper proposes a scheme that combines cloud computing with blockchain that assures data integrity for all homomorphic encryption schemes. To overcome the cloud service provider's (CSP) ultimate authority over the data, the proposed scheme relies on the Byzantine Fault Tolerance consensus to build a distributed network of processing CSPs based on the client requirements. After certain computations performed by all CSPs, they produce a master hash value for their database. To ensure immutable data is produced, master hash values are preserved in Bitcoin or Ethereum blockchain networks. The master hash values can be obtained by tracking the block header address for verification purposes. A theoretical analysis of the overhead costs associated with creating master hash values for each of the cryptocurrencies is presented. We found that Ethereum leads to lower client financial costs and better online performance than Bitcoin. We also specify the data security requirements the proposed scheme provides, the ground-level implementation, and future work. The proposed verification scheme is based on public cryptocurrency as a back-end service and does not require additional setup actions by the client other than a wallet for the chosen cryptocurrency.

Zhufeng Ye, Zhenghao Wu, Xianglan Tian

Privacy-preservation and effective auditing are two desirable but challenging requirements on distributed ledgers. To meet the requirements, this paper presents an auditing scheme, called as AudiTEE, which can audit a distributed ledger in a generic, efficient, and privacy-preserving manner. AudiTEE leverages Trusted Execution Environment (TEE) to generate confidential but auditable transactions and realize arbitrary, efficient and confidential audit on them. Unfortunately, TEE suffers from some inherent barriers and is itself not a complete solution for fast audit. To tackle these challenges, AudiTEE takes advantage of KAMT (K-anonymity Authentication Based on Merkle Tree) protocol for efficient management on account and user-defined anonymous transactions. Further, to achieve a complete and fast audit with unlinkability, TEE doesn’t process through all but only a comparatively small part of transactions according to a special ktag attached on each transaction to ensure that a user cannot hide transactions from auditor even when auditor is blind with who is involved in each transaction on the ledger. Apart from the above, AudiTEE allows flexible control on user behaviors. We implement a concrete instance of AudiTEE under a bank setting and demonstrate the scalability with all its core functionalities.

Rahul Saha, Gulshan Kumar, Tannishtha Devgun, William J. Buchanan · 8 authors

The decentralization and transparency have provided wide acceptance of blockchain technology in various sectors through numerous applications. The claimed security services by blockchain have been proved using various cryptographic techniques, mainly public key infrastructure and digital signatures. However, the use of generic cryptographic primitives using large prime numbers or elliptic curves with logarithms is going to be an issue with quantum computers as those techniques are vulnerable in post-quantum era. Therefore, the paradigm shift from pre-quantum to the post-quantum era has necessitated new cryptographic developments which are robust against quantum attacks and applicable in blockchain for post-quantum decentralization. Therefore, we have presented a solution for post-quantum decentralization in the blockchain. It uses lattices with polynomials for identity-based encryption (IBE) and aggregate signatures for the consensus to ensure efficiency and suitability in post-quantum blockchain applications. We experiment the proposed approach based on delay, throughput, energy consumption and complexity. The comparative results prove that the presented work is efficient.

Petr Kuznetsov, Yvonne-Anne Pignolet, Pavel Ponomarev, Andrei Tonkikh

Most modern asset transfer systems use consensus to maintain a totally ordered chain of transactions. It was recently shown that consensus is not always necessary for implementing asset transfer. More efficient, asynchronous solutions can be built using reliable broadcast instead of consensus. This approach has been originally used in the closed (permissioned) setting. In this paper, we extend it to the open (permissionless) environment. We present {Pastro}, a permissionless and asynchronous asset-transfer implementation, in which quorum systems, traditionally used in reliable broadcast, are replaced with a weighted Proof-of-Stake mechanism. {Pastro} tolerates a dynamic adversary that is able to adaptively corrupt participants based on the assets owned by them.

Danyang Liu, Anming Dong, Biwei Yan, Jiguo Yu

Access control is a technology that can guarantee the security of information in network transmission, in which role-based access control is to separate the subject from the permission, and to assign the permission by distributing the corresponding role of the user. However, the traditional role-based access control scheme is generally centralized, the allocation of user’s role lacks fine granularity, and there is static in the allocation of the role and permission, which is not consistent with the distributed and dynamic network architecture nowadays. Hence, we propose a dynamic and fine-grained role-based access control model DF-RBAC, which can realize the flexible assignment of roles by resource owners and security verification of assigned roles. Further, we take advantage of blockchain technology and cryptography technology to combine with the DF-RBAC framework to achieve access to the activity log security audit function, which can ensure the security of the overall architecture. By safety and experimental analysis, our framework has proved to be feasible.

Samuel Dittmer, Yuval Ishai, Rafail Ostrovsky

We introduce and study a simple kind of proof system called line-point zero knowledge (LPZK). In an LPZK proof, the prover encodes the witness as an affine line 𝐯(t) : = at + 𝐛 in a vector space 𝔽ⁿ, and the verifier queries the line at a single random point t = α. LPZK is motivated by recent practical protocols for vector oblivious linear evaluation (VOLE), which can be used to compile LPZK proof systems into lightweight designated-verifier NIZK protocols. We construct LPZK systems for proving satisfiability of arithmetic circuits with attractive efficiency features. These give rise to designated-verifier NIZK protocols that require only 2-5 times the computation of evaluating the circuit in the clear (following an input-independent preprocessing phase), and where the prover communicates roughly 2 field elements per multiplication gate, or roughly 1 element in the random oracle model with a modestly higher computation cost. On the theoretical side, our LPZK systems give rise to the first linear interactive proofs (Bitansky et al., TCC 2013) that are zero knowledge against a malicious verifier. We then apply LPZK towards simplifying and improving recent constructions of reusable non-interactive secure computation (NISC) from VOLE (Chase et al., Crypto 2019). As an application, we give concretely efficient and reusable NISC protocols over VOLE for bounded inner product, where the sender’s input vector should have a bounded L₂-norm.

Anatoly Konkin, Sergey Zapechnikov

Nowadays distributed ledger technology or blockchain is widely used in the corporate sector for various industries. Although implementation issues (coding practice, lack of capabilities, etc.) are not among the major barriers for the technology adaption, there are still some informational security challenges to adjust and scale blockchain networks for corporate usage. One of them is to provide functionality for private transactions stored in a blockchain. Some methods including mix networks, ring signatures, and off-chain protocols were applied to meet the privacy requirements. However, these methods have some limitations associated with the key blockchain characteristics such as decentralized storing system and immutability verification of private data. This article examines zero-knowledge proof (ZKP) methods for corporate blockchain networks. The article provides the review of existing methods for private transactions, discovers the implementation of ZKP methods, also performance and scalability issues are discussed.

Jianlin Niu, Zhiyu Ren

The existing self-sovereign identity management schemes have some problems, such as weak availability and security risks. To solve these problems, we proposed a cross-domain self-sovereign identity management scheme using smart contracts. This scheme takes into account the entire lifecycle of identity, especially including the cross-domain use and recovery. To preserve the privacy data of users on the blockchain, we proposed a data storage method of anchoring on blockchain. Finally, we implemented this scheme using the Solidity programming language for smart contract. This scheme has been experimentally verified to be capable of maintaining the expenditure of resources under control and having good usability. Compared with other self-sovereign identity management schemes, this scheme has better performance in terms of controllability, security and portability.

Thomas Attema, Ronald Cramer, Serge Fehr

No abstract is available for this record.

Yuki Nishida, Hiromasa Saito, Ran Chen, Akira Kawata · 7 authors

Abstract A smart contract is a program executed on a blockchain, based on which many cryptocurrencies are implemented, and is being used for automating transactions. Due to the large amount of money that smart contracts deal with, there is a surging demand for a method that can statically and formally verify them. This tool paper describes our type-based static verification tool Helmholtz for Michelson, which is a statically typed stack-based language for writing smart contracts that are executed on the blockchain platform Tezos. Helmholtz is designed on top of our extension of Michelson’s type system with refinement types. Helmholtz takes a Michelson program annotated with a user-defined specification written in the form of a refinement type as input; it then typechecks the program against the specification based on the refinement type system, discharging the generated verification conditions with the SMT solver Z3. We briefly introduce our refinement type system for the core calculus Mini-Michelson of Michelson, which incorporates the characteristic features such as compound datatypes (e.g., lists and pairs), higher-order functions, and invocation of another contract. Helmholtz successfully verifies several practical Michelson programs, including one that transfers money to an account and that checks a digital signature.

Stefan More, Peter Grassberger, Felix Hörandner, Andreas Abraham · 5 authors

Recruiters and institutions around the world struggle with the verification of diplomas issued in a diverse and global education setting. Firstly, it is a nontrivial problem to identify bogus institutions selling education credentials. While institutions are often accredited by qualified authorities on a regional level, there is no global authority fulfilling this task. Secondly, many different data schemas are used to encode education credentials, which represents a considerable challenge to automated processing. Consequently, significant manual effort is required to verify credentials. In this paper, we tackle these challenges by introducing a decentralized and open system to automatically verify the legitimacy of issuers and interpret credentials in unknown schemas. We do so by enabling participants to publish transformation information, which enables verifiers to transform credentials into their preferred schema. Due to the lack of a global root of trust, we utilize a distributed ledger to build a decentralized web of trust, which verifiers can query to gather information on the trustworthiness of issuing institutions and to establish trust in transformation information. Going beyond diploma fraud, our system can be generalized to tackle the generalized problem for other domains lacking a root of trust and agreements on data schemas.

Emanuel Onica, Cosmin-Ionuţ Schifirneţ

No abstract is available for this record.

Yuxin Zhong, Mi Zhou, Jiangnan Li, Jiahui Chen · 7 authors

Authentication and authorization (A & A) mechanisms are critical to the security of Internet of Things (IoT) applications. Smart grid system processing and exchanging data without human intervention, known as smart grids, are well‐known as IoT scenarios. Entities in such smart grid systems need to identify and validate one another and ensure the integrity of data exchange mechanisms. However, at present, most commonly used A & A protocols are centralized, resulting in security risks such as information leaks, illegal access, and identity theft. In this study, we propose a new distributed A & A protocol for smart grid networks based on blockchain technology to address with these risks. The proposed protocol integrates the decentralized authentication and immutable ledger characteristics of blockchain architectures suitable for power systems with a novel blockchain technique to realize both identity authentication and resource authorization for smart grid systems. We discuss the security of and threat models for prior A & A protocols and demonstrate how our protocol protects against these threats. We further demonstrate an approach to a real deployment of our A & A protocol using the FISCO consortium platform, applying algorithms from smart contract systems. Finally, we present the results of experimental simulations showing the efficacy and efficiency of our proposed protocol.

Mingyue Wang, Yu Guo, Chen Zhang, Cong Wang · 6 authors

Electronic Health Record (EHR) and its privacy have attracted widespread attention with the development of the healthcare industry in recent years. As locking medical data in a single healthcare center causes information isolation, healthcare centers are motivated to build medical data sharing systems. However, existing systems highly rely on the trusted centralized servers, which are vulnerable to distributed denial of service (DDoS) attacks and the single point of failure. Moreover, it is a non-trivial matter to authorize multiple users to search and access EHR in a privacy-preserving manner. In this paper, we propose MedShare, a decentralized framework for secure EHR sharing. Our design utilizes the smart contract technique of blockchain to establish a trusted platform for healthcare centers to share their encrypted EHR. Considering that fine-grained access control is essential in practical EHR sharing service, we devise a constant-size attribute-based encryption (ABE) scheme, where the access policy is embedded in search result on the blockchain. Besides, we propose an efficient scheme that enables authorized MedShare users to perform multi-keyword boolean search operations over encrypted EHR. We formally analyze the security strengths and implement the system prototype on Ethereum. Evaluation results demonstrate that MedShare is efficient for EHR sharing.

Sunoo Park, Michael A. Specter, Neha Narula, Ronald L. Rivest

Abstract Voters are understandably concerned about election security. News reports of possible election interference by foreign powers, of unauthorized voting, of voter disenfranchisement, and of technological failures call into question the integrity of elections worldwide. This article examines the suggestions that “voting over the Internet” or “voting on the blockchain” would increase election security, and finds such claims to be wanting and misleading. While current election systems are far from perfect, Internet- and blockchain-based voting would greatly increase the risk of undetectable, nation-scale election failures. Online voting may seem appealing: voting from a computer or smartphone may seem convenient and accessible. However, studies have been inconclusive, showing that online voting may have little to no effect on turnout in practice, and it may even increase disenfranchisement. More importantly, given the current state of computer security, any turnout increase derived from Internet- or blockchain-based voting would come at the cost of losing meaningful assurance that votes have been counted as they were cast, and not undetectably altered or discarded. This state of affairs will continue as long as standard tactics such as malware, zero day, and denial-of-service attacks continue to be effective. This article analyzes and systematizes prior research on the security risks of online and electronic voting, and shows that not only do these risks persist in blockchain-based voting systems, but blockchains may introduce ‘additional’ problems for voting systems. Finally, we suggest questions for critically assessing security risks of new voting system proposals.

Javier Herranz, Ramiro Pinilla, Manuel Sánchez-Raya

In an electronic voting procedure, mixing networks are used to ensure anonymity of the casted votes. Each node of the network re-encrypts the input list of ciphertexts and randomly permutes it in a process named shuffle, and must prove (in zero-knowledge) that the process was applied honestly. To maintain security of such a process in a post-quantum scenario, new proofs are based on different mathematical assumptions, such as lattice-based problems. Nonetheless, the best lattice-based protocols to ensure verifiable shuffling have linear communication complexity on N, the number of shuffled ciphertexts.

Akram Alkouz, Ahmed HajYasien, Abdulsalam Alarabeyyat, Khalid Samara · 5 authors

There has been a great deal of discussion of the challenges on privacy, data interoperability and quality of Educational Professional Personal Record (EPPR). Therefore, there is a need to reassess the current models, in which various parties generate, exchange and observe a huge amount of personal data with regard to EPPR. Ethereum blockchain has shown that trusted, auditable transactions is detectible using a decentralized network of nodes accompanied by a general ledger. Thus, due to the fast-moving development of educational and professional data generators such as online universities and distance learning, requires learners to engage in detail into their EPPR as well as the educational and professional data generators. In this paper, we propose a novel decentralized framework to manage EPPR using Ethereum blockchain technology. The framework provides the owner of the EPPR a comprehensive immutable log and ease of access to their educational records across the educational record editors and consumers. Furthermore, it provides a recommender engine to endorse skills and competencies to the education record owners and similar candidates for educational records editors and consumers. Ethereum blockchain can provide solutions in terms of exchanging of data among parties by ensuring privacy, accountability and data interoperability. The aim of the proposed framework is to enable educational stakeholders (universities and employing agencies) to participate in the network as blockchain miners rewarded by pseudonymized data in compliance with General Data Protection Rules in United Arab Emirates.

Chaosheng Feng, Keping Yu, Ali Kashif Bashir, Yasser D. Al‐Otaibi · 7 authors

The drone's open and untrusted environment may create problems for authentication and data sharing. To address this issue, we propose a blockchain-enabled efficient and secure data sharing model for 5G flying drones. In this model, blockchain and attribute-based encryption (ABE) are applied to ensure the security of instruction issues and data sharing. The authentication mechanism in the model employs a smart contract for authentication and access control, public key cryptography for providing accounts and ensuring accounts' security, and a distributed ledger for security audit. In addition, to speed up out-sourced computations and reduce electricity consumption, an ABE model with parallel outsourced computation (ABEM-POC) is constructed, and a generic parallel computation method for ABE is proposed. The analysis of the experimental results shows that parallel computation significantly improves the speed of outsourced encryption and decryption compared to serial computation.

Xavier Salleras, Vanesa Daza

Zero-Knowledge Proofs (ZKPs) are cryptographic primitives allowing a party to prove to another party that the former knows some information while keeping it secret. Such a premise can lead to the development of numerous privacy-preserving protocols in different scenarios, like proving knowledge of some credentials to a server without leaking the identity of the user. Even when the applications of ZKPs were endless, they were not exploited in the wild for a couple of decades due to the fact that computing and verifying proofs was too computationally expensive. However, the advent of efficient schemes (in particular, zk-SNARKs) made this primitive to break into the scene in fields like cryptocurrencies, smart-contracts, and more recently, self-sovereign scenarios: private-by-design identity management and authentication. Nevertheless, its adoption in environments like the Internet of Things (IoT) remains unexplored due to the computational limitations of embedded systems. In this paper, we introduce ZPiE, a C library intended to create ZKP applications to be executed in embedded systems. Its main feature is portability: it can be compiled, executed, and used out-of-the-box in a wide variety of devices. Moreover, our proof-of-concept has been proved to work smoothly in different devices with limited resources, which can execute state-of-the-art ZKP authentication protocols.

Daniel Benarroch, Matteo Campanelli, Dario Fiore, Kobi Gurkan · 5 authors

Abstract We consider the problem of proving in zero knowledge that an element of a public set satisfies a given property without disclosing the element, i.e., for some u , “ $$u \in S$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>u</mml:mi><mml:mo>∈</mml:mo><mml:mi>S</mml:mi></mml:mrow></mml:math> and P ( u ) holds”. This problem arises in many applications (anonymous cryptocurrencies, credentials or whitelists) where, for privacy or anonymity reasons, it is crucial to hide certain data while ensuring properties of such data. We design new modular and efficient constructions for this problem through new commit-and-prove zero-knowledge systems for set membership , i.e. schemes proving $$u \in S$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>u</mml:mi><mml:mo>∈</mml:mo><mml:mi>S</mml:mi></mml:mrow></mml:math> for a value u that is in a public commitment $$c_u$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>c</mml:mi><mml:mi>u</mml:mi></mml:msub></mml:math> . We also extend our results to support non-membership proofs , i.e. proving $$u \notin S$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>u</mml:mi><mml:mo>∉</mml:mo><mml:mi>S</mml:mi></mml:mrow></mml:math> . Being commit-and-prove, our solutions can act as plug-and-play modules in statements of the form “ $$u \in S$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>u</mml:mi><mml:mo>∈</mml:mo><mml:mi>S</mml:mi></mml:mrow></mml:math> and P ( u ) holds” by combining our set (non-)membership systems with any other commit-and-prove scheme for P ( u ). Also, they work with Pedersen commitments over prime order groups which makes them compatible with popular systems such as Bulletproofs or Groth16. We implemented our schemes as a software library, and tested experimentally their performance. Compared to previous work that achieves similar properties—the clever techniques combining zkSNARKs and Merkle Trees in Zcash—our solutions offer more flexibility, shorter public parameters and $$3.7 \times $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>3.7</mml:mn><mml:mo>×</mml:mo></mml:mrow></mml:math> – $$30\times $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>30</mml:mn><mml:mo>×</mml:mo></mml:mrow></mml:math> faster proving time for a set of size $$2^{64}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mn>2</mml:mn><mml:mn>64</mml:mn></mml:msup></mml:math> .