Bitcoinin julkaisu merkitsi samalla lohkoketjusovellusten syntymää. Johtuen muun muassa julkisen todennettavuuden tarpeesta, lohkoketjussa säilytettävä tieto on tyypillisesti läpinäkyvää, joka voi olla ongelmallista yksityisyyden kannalta. Yksityisyyden parantamiseksi on kehitetty menetelmiä, jotka hämärtävät lohkoketjun tietojen läpinäkyvyyttä säilyttäen niiden eheyden ja todennettavuuden. Lupaava kryptografinen menetelmä tähän tarkoitukseen on nollatietotodistus, joka mahdollistaa väitteen todistamisen siten, että ainoa todistuksessa paljastuva tieto on väitteen totuusarvo. \n \nNollatietotodistuksiin perehtyminen aloitetaan niiden teoreettisesta perustasta. Lohkoketjujen kannalta tärkeitä vaatimuksia nollatietotodistuksille ovat ei-interaktiivisuus ja ytimekkyys, ja nämä ehdot täyttäviä todistusrakenteita kutsutaan yleisesti nimellä zk-SNARK. Fiat-Shamir muunnos on käyttökelpoinen menetelmä ei-interaktiivisen nollatietotodistuksen muodostamiseen tapauksissa, joissa ytimekkyys ei ole tärkeää. Nollatietotodistusten käyttöä tutkitaan erityisesti yksityisyyden ja käyttökelpoisuuden kannalta kolmessa lohkoketjusovelluksessa, jotka ovat Zcash, Ethereum ja Monero.
Zero-knowledge proofs have always provided a clear solution when it comes to conveying information from a prover to a verifier or vice versa without revealing essential information about the process. Advancements in zero-knowledge have helped develop proofs which are succinct and provide non-interactive arguments of knowledge along with maintaining the zero-knowledge criteria. zk-SNARKs (Zero knowledge Succinct Non-Interactive Argument of Knowledge) are one such method that outshines itself when it comes to advancement of zero-knowledge proofs. The underlying principle of the Zcash algorithm is such that it delivers a full-fledged ledger-based digital currency with strong privacy guarantees and the root of ensuring privacy lies fully on the construction of a proper zk-SNARK. In this paper we elaborate and construct a concrete zk-SNARK proof from scratch and explain its role in the Zcash algorithm.
Haya R. Hasan, Khaled Salah, Raja Jayaraman, Raja Wasim Ahmad · 6 authors
Spare parts are essential assets to maintain productivity and operations. A spare part is used for the repair or replacement of failed units. Tracing and tracking of spare parts ownership can help to ensure reliable outcomes in terms of manufacturing operations and service delivery. However, today's spare part inventory systems fall short of providing reliable tracing and tracking of spare parts ownership which poses serious threats to their authenticity. Also, current approaches and systems leveraged for spare part inventory management are vulnerable to the single point of failures. In this paper, we propose a blockchain-based smart contract to trace and track the spare parts ownership details from the original equipment manufacturer to the supplier and end-users. We exploit blockchain features to build a secure and trusted spare part inventory system that is tamper-proof, traceable, trackable, accessible immutable, resilient, and reliable. The proposed system integrates decentralized storage of interplanetary file systems (IPFS) to store and share spare parts data. We present algorithms along with their full implementation details. We perform testing and validation of the smart contract. Furthermore, we provide security and cost analysis, and show how the proposed system ensures reliable tracing and tracking of spare parts ownership. We make the smart contract source code publicly available on Github.
Tingting Song, Bo Cui, Ru Li, Jing Liu · 5 authors
Named Data Networking (NDN) is a new clean-slate architecture for the future Internet. Efficient content retrieval is the original intention of NDN design. The content retrieval process driven by content consumers in NDN includes the following challenges, consumers do not know whether the content exists and whether the content producer is reliable. Invalid interest packets could cause the occupation of limited network resources and DoS attack problem. To ensure the authenticity and integrity of the data packets, consumers need to pre-configure the trust schema, which is centralized and prone to the single point of failure problem. Blockchain has widespread attention to build trust in a distributed way, and Ethereum is a programmable blockchain, a decentralized smart contract platform. To lighten the burden of consumers, we proposed a Smart Contract-based Trusted Content Retrieval Mechanism (SCTCRM) for NDN in this paper. The mechanism contains a trustworthy information base for content and producers based on smart contracts, and provides content retrieval and name resolution services for content consumers. The purpose of this mechanism is to improve the efficiency and security of content retrieval process. We described the framework and the workflow of SCTCRM, and used Colored Petri Nets to create a formal mathematical model and analyze the security of the mechanism. Finally, the cost of storage and Gas in smart contracts are evaluated through the prototype deployment. From the results, we can see that the proposed mechanism is security and practicality.
Electronic medical records (EMRs) are electronically-stored highly sensitive and private information related to the diagnosis and treatment of patient, and needs to be frequently shared among peers. Sharing of medical records between participants is very challenging because the data might be revealed or tampered during the operational process. To address these challenges, a blockchain-based electronic medical records system is the key solution. In this research, we have discussed how blockchain technology can help in better healthcare data management. We have proposed a blockchain-based records management system for efficient management and sharing of electronic medical records (EMRs). We have implemented a prototype of Electronic Medical Records Management System using permissioned blockchain platform “Hyperledger”. This system ensures privacy, security and easy accessibility and availability of medical records.
We survey the state-of-the-art non-interactive zero-knowledge argument schemes and their applications in confidential transactions and private smart contracts on blockchain. The main goal of this paper is to serve as a reference for blockchain application developers in finding the most suitable scheme for a particular use case. We give an overview and compare the state-of-the-art protocols for confidential transactions and private smart contracts regarding the protection of the transaction graph and amounts, data and functionality. However, our main focus is on state-of-the-art zero-knowledge argument schemes. We briefly describe their backgrounds, proof lengths and computational complexities and discuss their cryptographic security models. Our focus is on seminal, otherwise notable and, especially, implemented methods that are ready to be applied in practice. We also survey the existing implementations of transforming computations into circuit representations required by those methods. We note that the existing schemes have different strengths and drawbacks regarding usability, setup, proof length and proving and verification costs.
Blockchain technologies enable decentralized applications (DApps) that run on distributed infrastructures without any central authority. All transactions for communication and data storage are public and can be verified by all participants. DApps interacting with a smart contract typically require client-side code, which is not part of the smart contract, and therefore do not hold the same verifiability properties. Following the vision of a verifiable DApp, we propose SmartDHX, a Diffie-Hellman key exchange (DHKE) scheme, fully implemented as a smart contract. That is, SmartDHX communicates only via the Ethereum blockchain and provides both backend and client-side code with the smart contract. The application code can therefore be verified and deployed without external trust requirements. By executing DHKE on-chain, we gain a number of properties, including asynchronicity as well as message integrity and authenticity. We generalize the two-party SmartDHX to emphasize that our approach is able to handle complex cryptographic protocols. In our analysis, we expose an efficiency tradeoff when executed on chain. In particular, we provide a proof-of-concept implementation and analyze the runtime and transaction fees. Since DHKE is used by many cryptographic algorithms, SmartDHX contributes a fundamental building block in the domain of DApps.
The Internet of Things (IoT) is a network that integrates a variety of heterogeneous nodes, such as connected devices (sensors, robots, and smart phones ...), connected cars, smart homes, etc. These smart objects communicate and collaborate in distributed and dynamic environments that are facing several security challenges. Trust management is one of the most important challenges in IoT. Existing trust management solutions do not meet the new requirements of IoT such as heterogeneity, mobility, and scalability. In this article, we propose a hierarchical and scalable blockchain-based trust management protocol with mobility support in massively distributed IoT systems. In our protocol, mobile smart objects disseminate trust information on service providers to the blockchain. Thus, all the objects will have a global view on each service provider in the architecture, which speeds up the trust evaluation process. In addition, our protocol is resilient against the most known malicious attacks such asbad-mouthing,ballot-stuffing, andcooperative attacks. We confirm the efficiency of our proposal through theoretical analysis and extensive simulations. Finally, we show that it outperforms existing solutions, especially in terms of scalability, mobility support, communication, and computation costs.
The healthcare industry electronically maintains medical data which includes patients' information such as patients' personal information, diagnostic reports, and doctor prescriptions. However, the centralized storage model is currently used for storing such sensitive information. One main disadvantage of the centralized model is the difficulty in preserving user privacy. Threats relating to user (patient) privacy include unauthorized access of critical information such as identity details and diseases from which a patient is suffering, and misuse of patients' data and their medical reports. To address this issue, we propose a distributed off-chain storage of medical data using IPFS (Interplanetary File System) and blockchain technology. The proposed framework while preserving patient privacy facilitates easy access of medical data by authorized entities such as healthcare providers (e.g., doctors and nurses). Moreover, it achieves consistency, integrity, and availability.
In Internet of Things ecosystems, where various entities trade data and data analysis results, public key infrastructure plays an important role in establishing trust relationships between these entities to specify who trusts whose private keys. The owner of a private key is provided with a public key certificate issued by a certificate authority (CA) representing a trusted third party. Although this certificate ensures the reliability of the ecosystem by verifying the data source and preventing the denial of trading, it often causes an overconcentration of trust in a particular CA. Consequently, if that CA is infringed, all the related trust relationships become compromised. The paper proposes a distributed authentication infrastructure called Meta-PKI that decentralizes such overconcentration via a cross-certification procedure performed by multiple CAs. Although cross-certification is capable of establishing mutual trust relationships, it does not evaluate the trustworthiness of other CAs in a standardized manner. Therefore, this paper also proposes a new cross-certification method using a distributed ledger technology for building trust relationships based on unified criteria. It also describes the implementation of a Meta-PKI system for Hyperledger Fabric as a proof of concept. Once trust relationships have been established, it takes approximately 65.7 ms to validate them using the proposed system, which is secure against CA takeover and spoofing by outsider attackers.
In blockchain, transactions between parties are regrouped into blocks, in order to be added to the blockchain's distributed ledger. Miners are nodes of the network that generate new blocks that meet the consensus protocol. Thus, when a miner adds a valid block to the distributed ledger, the miner is rewarded. Due to the difficulty of the problem to be solved by the miner in order to find a valid block, it becomes difficult to a single miner to gain rewards. Therefore, miners join mining pools, where the powers of miners are federated to ensure stable revenues for miners. In public blockchains, access to mining pools is not restricted, which makes mining pools vulnerable to considerable threats such as: block withholding (BWH) attacks and distributed denial of service (DDoS) attacks. In the present work, we a new blockchain named PoolCoin that manages reputation in mining pools. In addition, we provide a trust model for PoolCoin, inspired by the job market signaling model. The proposed PoolCoin blockchain allows pool managers to accept trusted miners in their mining pools, while miners are able to evaluate pool managers. The performance evaluation is conducted and the obtained simulation results are presented and discussed. In order to study the efficiency of the proposed trust model, a performance evaluation was provided. Thus, the model parameters' are optimized in order to detect and exclude misbehaving miners, while honest miners are maintained in the mining pool.
OAuth 2.0 is the industry-standard protocol for authorization. It facilitates secure service provisioning, as well as secure interoperability among diverse stakeholders. All OAuth 2.0 protocol flows result in the creation of an access token, which is then used by a user to request access to a protected resource. Nevertheless, the definition of access tokens is transparent to the OAuth 2.0 protocol, which does not specify any particular token format, how tokens are generated, or how they are used. Instead, the OAuth 2.0 specification leaves all these as design choices for integrators. In this paper, we propose a new type of OAuth 2.0 token backed by a distributed ledger. Our construction is secure, and it supports proof-of-possession, auditing, and accountability. Furthermore, we provide added-value token management services, including revocation, delegation, and fair exchange by leveraging smart contracts. We realized a proof-of-concept implementation of our solution using Ethereum smart contracts and the ERC-721 token specification.
Electronic health record (EHR) management systems require the adoption of effective technologies when health information is being exchanged. Current management approaches often face risks that may expose medical record storage solutions to common security attack vectors. However, healthcare-oriented blockchain solutions can provide a decentralized, anonymous and secure EHR handling approach. This paper presents PREHEALTH, a privacy-preserving EHR management solution that uses distributed ledger technology and an Identity Mixer (Idemix). The paper describes a proof-of-concept implementation that uses the Hyperledger Fabric's permissioned blockchain framework. The proposed solution is able to store patient records effectively whilst providing anonymity and unlinkability. Experimental performance evaluation results demonstrate the scheme's efficiency and feasibility for real-world scale deployment.
Blockchain is widely recognized as a potential disruptive technology that has gained much popularity recently. Despite many promising results, the current blockchain landscape is fragmented, in which many blockchain systems exist in silos. Interoperability becomes a critical functionality to facilitate broad blockchain adoption and starts to attract attention in both industry and academia research. In this paper, we propose a new consensus protocol, Multi-tokens Proof of Stake (MPoS), for blockchain interoperability architecture. The MPoS protocol is able to strengthen the token network effects in a cross-chain ecosystem and grow the user base of blockchain systems dramatically. We also provide an analytical model to analyze and prove that the MPoS protocol can offer better security than traditional single-token PoS consensus protocols.