Blockchain Papers

Furqan Shahid, Abid Khan, Saif Ur Rehman Malik, Kim‐Kwang Raymond Choo

No abstract is available for this record.

Stavros Kassaras, Λέανδρος Μαγλαράς

How someone can get health insurance without sharing his health information? How you can get a loan without disclosing your credit score? There is a method to certify certain attributes of various data, either this is health metrics or finance information, without revealing the data itself or any other kind of personal data. This method is known as zero-knowledge proofs. Zero-Knowledge techniques are mathematical methods used to verify things without sharing or revealing underlying data. Zero-Knowledge protocols have vast applications from simple identity schemes and blockchains to defense research programs and nuclear arms control

Can Özturan

Direct bartering allows for the trading of assets with or without the use of money. In this paper, we introduce a smart contract written in the Solidity language for the Ethereum blockchain that implements a distributed and autonomous direct barter exchange operated by crowds. Since ERC20 smart contract tokens are widely used for initial coin offerings (ICOs), our implementation provides autonomous bartering services for ERC20 tokens. The non-fungible ERC721 token, as well as Ethereum Name Service (ENS) name bartering, are also supported. Because finding a feasible bartering solution for bids involving multiple tokens is NP-hard in general, our exchange only provides escrow and swapping services. It assumes feasible solutions are submitted by bartering problem solvers from the crowd who run a solver locally on their machines. Bartering problem solvers are incentivized to submit solutions to the autonomous exchange by awarding them with excess tokens that are left over after granting the bidders the tokens they requested in their bids. Our system, called BarterMachine, can perhaps be used to facilitate a global barter economy. The BarterMachine prototype is available for testing on the Ethereum Ropsten network at https://bartermachine.github.io/bartermachine/ropsten/.

César Sabater, Aurélien Bellet, Jan Ramon

Learning from data owned by several parties, as in federated learning, raises challenges regarding the privacy guarantees provided to participants and the correctness of the computation in the presence of malicious parties. We tackle these challenges in the context of distributed averaging, an essential building block of federated learning algorithms. Our first contribution is a scalable protocol in which participants exchange correlated Gaussian noise along the edges of a network graph, complemented by independent noise added by each party. We analyze the differential privacy guarantees of our protocol and the impact of the graph topology under colluding malicious parties, showing that we can nearly match the utility of the trusted curator model even when each honest party communicates with only a logarithmic number of other parties chosen at random. This is in contrast with protocols in the local model of privacy (with lower utility) or based on secure aggregation (where all pairs of users need to exchange messages). Our second contribution enables users to prove the correctness of their computations without compromising the efficiency and privacy guarantees of the protocol. Our verification protocol relies on standard cryptographic primitives like commitment schemes and zero knowledge proofs.

Marcela Tuler de Oliveira, Lúcio Henrik A. Reis, Dianne S. V. Medeiros, Ricardo C. Carrano · 6 authors

Consensus mechanisms in blockchain applications allow mistrusting peers to agree on the global state of the chain. Most of the existing consensus mechanisms, however, are constrained by low efficiency and high energy consumption. In this paper, we propose the Blockchain Reputation-Based Consensus (BRBC) mechanism in which a node must have the reputation score higher than a given network trust threshold before being allowed to insert a new block in the chain. A randomly-selected set of judges monitors the behaviour of each node involved in the consensus and updates the node reputation score. Every cooperative behaviour results in a reward, and a non-cooperative or malicious behaviour results in a punishment. BRBC also uses the reputation score to revoke access to nodes with a reputation score below a given threshold. We present a security analysis, and we demonstrate that BRBC resists against a set of known attacks in the blockchain network. Finally, we simulate a blockchain network to assert the mechanism scalability and resilience to malicious actions in various network scenarios and different rates of malicious actions. The results show BRBC to be efficient to expel all nodes that acted with more than 50% of malicious actions.

Guangsheng Yu, Xuan F. Zha, Xu Wang, Wei Ni · 7 authors

No abstract is available for this record.

Hyunjun Jung, Heung-No Lee

Bitcoin is the first cryptocurrency to participate in a network and receive compensation for online remittance and mining without any intervention from a third party, such as financial institutions. Bitcoin mining is done through proof of work (PoW). Given its characteristics, the higher hash rate results in a higher probability of mining, leading to the emergence of a mining pool, called a mining organization. Unlike central processing units or graphics processing units, high-cost application-specific integrated circuit miners have emerged with performance efficiency. The problem is that the obtained hash rate exposes Bitcoin’s mining monopoly and causes the risk of a double-payment attack. To solve this problem, we propose the error-correction code PoW (ECCPoW), combining the low-density parity-check decoder and hash function. The ECCPoW contributes to the phenomenon of symmetry in the proof of work (PoW) blockchain. This paper proposes the implementation of ECCPoW, replacing the PoW in Bitcoin. Finally, we compare the mining centralization, security, and scalability of ECCPoW and Bitcoin.

Antoine Rondelet

In this note, we remark that the aggregation property of the BLS signature scheme yields an efficient Content Extraction Signature (CES). This construction can be used to build digital credentials that support selective disclosure in various settings. Interestingly, this construction is efficient and well suited to build credential issuance schemes with various applications in the client-server or in the distributed ledger models. Finally, we sketch a protocol that combines the CES with the use of a NIZK which allows to prove predicate satisfaction on claims extracted from a credential, while keeping the data secret.

Zoltán Lux, Dirk Thatmann, Sebastian Zickau, Felix Beierle

Authentication with username and password is becoming an inconvenient process\nfor the user. End users typically have little control over their personal\nprivacy, and data breaches effecting millions of users have already happened\nseveral times. We have implemented a proof of concept decentralized OpenID\nConnect Provider by marrying it with Self-Sovereign Identity, which gives users\nthe freedom to choose from a very large pool of identity providers instead of\njust a select few corporations, thus enabling the democratization of the highly\ncentralized digital identity landscape. Furthermore, we propose a verifiable\ncredential powered decentralized Public Key Infrastructure using distributed\nledger technologies, which creates a straightforward and verifiable way for\nretrieving digital certificates.\n

Mohsin Ur Rahman, Barbara Guidi, Fabrizio Baiardi

No abstract is available for this record.

Daniël Reijsbergen, Paweł Szałachowski, Junming Ke, Zengpeng Li · 5 authors

We present ProPoS, a Proof-of-Stake protocol dedicated, but not limited, to cryptocurrencies. ProPoS is a chain-based protocol that minimizes interactions between nodes through lightweight committee voting, resulting in a more simple, robust, and scalable proposal than competing systems. It also mitigates other drawbacks of previous systems, such as high reward variance and long confirmation times. ProPoS can support large node numbers by design, and provides probabilistic safety guarantees whereby a client makes commit decisions by calculating the probability that a transaction is reverted based on its blockchain view. We present a thorough analysis of ProPoS and report on its implementation and evaluation. Furthermore, our new technique of proving safety can be applied more broadly to other Proof-of-Stake protocols.

Authors unavailable

Blockchain technology allows the formation of a distributed record of a digital event in a decentralized manner where no third-party controls data and related transactions. This technology was used early for value transfer but now it has a wide range of applications in various fields such as healthcare, banking, the internet of things and many more. In the education sector, it gives numerous chances for decentralized management of records in educational institutions. Certificates distributed in colleges or universities are mostly hard copy. Students submit these certificates while applying for jobs at public or private sectors, where all these certificates are needed to be verified manually, it is very time-consuming process. There can be incidents where students may produce the fake certificate and it is difficult to identify them. This problem of fake academic certificates has been a longstanding issue in the academic community. There are chances that some may have produce the certificate which is not legit and that may get unnoticed by the verifier during the verification process. Because of the above situation, ineligible candidate will get a chance illegally. The key issues in Certificate verification for Workplace, banks and other businesses are in storage, retrieval and access to data with security. Blockchain technology can be enforced to solve these troubles in storing and accessing of data. This technology provides a common shared platform from where to store, retrieve and access documents securely. The very nature of the technology is in the distributed, shared, open ledgers, verifiable by all. This problem can be solved by storing the digital certificates on the Blockchain.

Daniël Reijsbergen, Paweł Szałachowski, Junming Ke, Zengpeng Li · 5 authors

We present Large-scale Known-committee Stake-based Agreement (LaKSA), a chain-based Proof-of-Stake protocol that is dedicated, but not limited, to cryptocurrencies. LaKSA minimizes interactions between nodes through lightweight committee voting, resulting in a simpler, more robust, and more scalable proposal than competing systems. It also mitigates other drawbacks of previous systems, such as high reward variance and long confirmation times. LaKSA can support large numbers of nodes by design, and provides probabilistic safety guarantees in which a client makes commit decisions by calculating the probability that a transaction is reverted based on its blockchain view. We present a thorough analysis of LaKSA and report on its implementation and evaluation. Furthermore, our new technique of proving safety can be applied more broadly to other Proof-of-Stake protocols.

Nasser Alsalami, Bingsheng Zhang

Public blockchains can be abused to covertly store and disseminate potentially harmful digital content which poses a serious regulatory issue. In this work, we show the severity of the problem by demonstrating that blockchains can be exploited to surreptitiously distribute arbitrary content. More specifically, all major blockchain systems use randomized cryptographic primitives, such as digital signatures and non-interactive zero-knowledge proofs; we illustrate how the uncontrolled randomness in such primitives can be maliciously manipulated to enable covert communication and hidden persistent storage. To clarify the potential risk, we design, implement and evaluate our technique against the widely-used ECDSA signature scheme, the CryptoNote's ring signature scheme, and Monero's ring confidential transactions. Importantly, the significance of the demonstrated attacks stems from their undetectability, their adverse effect on the future of decentralized blockchains, and their serious repercussions on users' privacy and crypto funds. Finally, we present a generic framework to immunize blockchains against these attacks.

Hasan Gül

Blok zincir (Blockchain) teknolojisinin bir ürünü olarak ortaya çıkan Bitcoin ve türevi kripto paralar son on yılın en önemli ekonomik yeniliğidir. Bitcoin, eşler arası veri paylaşım ağını (Peer-to-Peer) temel alan, merkezi bir otorite tarafından kontrol edilmeyen (decentralized), kamuya açık hesap kaydı tutma özelliğine sahip (PublicLedger), temelde online ödeme yapmayı sağlayan sanal bir para birimidir. Bitcoin, kripto paraların ekonomik olarak tanınmasında temel teşkil etmiştir. Bununla birlikte günümüzde genel veya özel fonksiyonlu pek çok Bitcoin türevi (Altcoin) kripto para birimi geliştirilmiştir. Kripto paralar her geçen gün daha fazla sayıda ticari işlemde kullanılmaya başlanmıştır. Kripto paralarla yapılan işlemlerin nasıl muhasebeleştirileceğine ilişkin henüz belirgin bir düzenleme bulunmaması farklı yaklaşımları da beraberinde getirmektedir. Bu çalışmanın amacı, mevcut yaklaşımlar ışığında kripto paraların nasıl muhasebeleştirilebileceğini tartışmaktır.<br>

Wan Yeon Lee

Recently the blockchain technology has been actively studied due to its great potentiality. The smart contract is a key mechanism of the blockchain system. Due to the short history of the smart contract, many issues have not been solved yet. One main issue is vulnerability and another main issue is cost optimization. While the vulnerability of smart contract has been actively studied, the cost optimization has been rarely studied. In this paper, we propose two cost optimization methods for smart contracts running on the blockchain system. Triggering a function in a smart contract program code may require costs and it is repeated continuously. So the minimization of costs required to trigger a function of smart contract while maintaining the performance equally is very important. The proposed two methods minimize the usage of expensive permanent variables deployed on the blockchain system. We apply the proposed two methods to three prevalent blockchain platforms: Ethereum, Klaytn and Tron. Evaluation experiments verify that the proposed scheme significantly reduces the costs of functions in the smart contract written with Solidity.

Wei Wu, Erwu Liu, Xinglin Gong, Rui Wang

With the development of precise positioning technology, a growing number of location-based services (LBSs) facilitate people's life. Most LBSs require proof of location (PoL) to prove that the user satisfies the service requirement, which exposes the user's privacy. In this paper, we propose a zero-knowledge proof of location (zk-PoL) protocol to better protect the user's privacy. With the zk-PoL protocol, the user can choose necessary information to expose to the server, so that hierarchical privacy protection can be achieved. The evaluation shows that the zk-PoL has excellent security to resist main attacks, moreover the computational efficiency is independent of input parameters and the zk-PoL is appropriate to delay-tolerant LBSs.

Rui Xie, Yuhui Wang, Mingzhou Tan, Wei Zhu · 7 authors

Traditional paper certificates and electronic certificates have difficulties in preservation and management, not to mention other problems concerning inconvenient verification, poor reliability, anti-counterfeiting and anti-tampering. This paper proposes a scheme designed to build a decentralized certificate system that is based on blockchain technology and smart contract, in which a set of blockchain certificate system aiming at providing blockchain certificate services for college students' innovation and entrepreneurship competition is developed. In this system, certain functions of the certificate about management, issuing, verification and revocation are realized via smart contract. Signer information, certificate template and certificate information are stored in a smart contract that adopts structured data, thereby realizing more convenient callings in querying and validating certificate.

Alevtina Dubovitskaya, Furqan Baig, Zhigang Xu, Rohit Shukla · 15 authors

BACKGROUND: With increased specialization of health care services and high levels of patient mobility, accessing health care services across multiple hospitals or clinics has become very common for diagnosis and treatment, particularly for patients with chronic diseases such as cancer. With informed knowledge of a patient's history, physicians can make prompt clinical decisions for smarter, safer, and more efficient care. However, due to the privacy and high sensitivity of electronic health records (EHR), most EHR data sharing still happens through fax or mail due to the lack of systematic infrastructure support for secure, trustable health data sharing, which can also cause major delays in patient care. OBJECTIVE: Our goal was to develop a system that will facilitate secure, trustable management, sharing, and aggregation of EHR data. Our patient-centric system allows patients to manage their own health records across multiple hospitals. The system will ensure patient privacy protection and guarantee security with respect to the requirements for health care data management, including the access control policy specified by the patient. METHODS: We propose a permissioned blockchain-based system for EHR data sharing and integration. Each hospital will provide a blockchain node integrated with its own EHR system to form the blockchain network. A web-based interface will be used for patients and doctors to initiate EHR sharing transactions. We take a hybrid data management approach, where only management metadata will be stored on the chain. Actual EHR data, on the other hand, will be encrypted and stored off-chain in Health Insurance Portability and Accountability Act-compliant cloud-based storage. The system uses public key infrastructure-based asymmetric encryption and digital signatures to secure shared EHR data. RESULTS: In collaboration with Stony Brook University Hospital, we developed ACTION-EHR, a system for patient-centric, blockchain-based EHR data sharing and management for patient care, in particular radiation treatment for cancer. The prototype was built on Hyperledger Fabric, an open-source, permissioned blockchain framework. Data sharing transactions were implemented using chaincode and exposed as representational state transfer application programming interfaces used for the web portal for patients and users. The HL7 Fast Healthcare Interoperability Resources standard was adopted to represent shared EHR data, making it easy to interface with hospital EHR systems and integrate a patient's EHR data. We tested the system in a distributed environment at Stony Brook University using deidentified patient data. CONCLUSIONS: We studied and developed the critical technology components to enable patient-centric, blockchain-based EHR sharing to support cancer care. The prototype demonstrated the feasibility of our approach as well as some of the major challenges. The next step will be a pilot study with health care providers in both the United States and Switzerland. Our work provides an exemplar testbed to build next-generation EHR sharing infrastructures.

Pascal Lafourcade, Marius Lombard-Platet

No abstract is available for this record.

Ioannis Sfyrakis, Thomas Groß

Current cloud and network infrastructures do not employ privacy-preserving methods to protect their assets. Anonymous credential schemes are a cryptographic building block that enables the certification of data structures and prove properties over their representations without disclosing the innards of their data structures in zero-knowledge. The GRaph Signature (GRS) scheme enables the certification and proof methods to sign infrastructure topologies represented as graph data structures and use zero-knowledge to prove properties over their certificates. As such, they represent a powerful privacy-preserving method that proves properties over a signed topology graph to another party without disclosing the blueprint of its topology. In this paper, we report our efforts in designing, implementing and benchmarking a Graph Signature Library (GSL). GSL is a cryptographic library realized in Java that implements the graph signature scheme.

Tatsuya Sasaki, Daiki Miyahara, Takaaki Mizuki, Hideaki Sone

In 2009, Gradwohl, Naor, Pinkas, and Rothblum proposed physical zero-knowledge proof protocols for Sudoku. That is, for a puzzle instance of Sudoku, their excellent protocols allow a prover to convince a verifier that there is a solution to the Sudoku puzzle and the prover knows it, without revealing any information about the solution. The possible drawback is that the existing protocols have an extractability error with a non-zero probability, or need special cards (such as scratch-off cards). Thus, in this study, we propose new protocols to perform zero-knowledge proof of knowledge for Sudoku using a normal deck of playing cards with no extractability error. Our protocols can be easily implemented by humans with a reasonable number of playing cards.

Yue Liu, Qinghua Lu, Hye-Young Paik, Xiwei Xu

Self-sovereign identity is a new identity management paradigm that allows entities to really have the ownership of their identity data and control their use without involving any intermediary. Blockchain is an enabling technology for building self-sovereign identity systems by providing a neutral and trustable storage and computing infrastructure, and can be viewed as a component of the systems. Both blockchain and self-sovereign identity are emerging technologies which could present a steep learning curve for architects. We collect and propose 12 design patterns for blockchain-based self-sovereign identity systems to help the architects understand and easily apply the concepts in system design. Based on the lifecycles of three main objects involved in self-sovereign identity, we categorise the patterns into three groups: key management patterns, decentralised identifier management patterns, and credential design patterns. The proposed patterns provide a systematic and holistic guide for architects to design the architecture of blockchain-based self-sovereign identity systems.

Jacob Swambo, Spencer Hommel, Bob McElrath, Bryan Bishop

A bitcoin \textit{covenant} is a mechanism to enforce conditions on future bitcoin transactions. A bitcoin \textit{vault} is a specific type of covenant transaction that enforces a time-lock on the transfer of control of funds to a hot wallet, but enables an immediate transfer of funds into a deep cold recovery wallet. This paper demonstrates how to integrate a bitcoin vault into a custody protocol and demonstrates the security properties of that protocol. The vault is implemented using pre-signed transactions with secure key deletion (as proposed in \cite{Swambo2020cov}). It is shown that vault-custody protocols enable the wallet owner to specify their desired balance for an inherent trade-off between the security of and accessibility of bitcoin holdings by adjusting the length of time-locks used. It is also demonstrated that wallet owners have increased control of risk-management by compartmentalizing funds across numerous vault transactions. While it isn't realistic to completely prevent theft, the most likely theft scenarios (compromising the hot wallet) have severely limited profitability for an attacker, deterring attempts at theft from the beginning. The proposed architecture was designed to offer defence-in-depth through redundancy and fault-tolerant functionality as well as countermeasures for class breaks through diversity across hardware and software layers. Finally, the architecture employs a detection (a watchtower) and response system that enables fail-safe recovery from attempted or partial thefts through a second type of covenant transaction, a push-to-recovery-wallet transaction.