Blockchain Papers

Kai Fan, Shangyang Wang, Yanhui Ren, Hui Li · 5 authors

No abstract is available for this record.

Yinghui Zhang, Robert H. Deng, Ximeng Liu, Dong Zheng

No abstract is available for this record.

Amadou Moctar Kane

By comparing cryptocurrencies with other existing payment methods, including banknotes and bank cards, it is clear that the use of Bitcoin and its competitors (Ethereum, \dots) is almost insignificant in world trade. We may also note that these cryptocurrencies have become tools of speculation, which is the antithesis of their primary purpose. Based essentially on the security of electronic signatures, the Ecash introduced here will put the users back to the center of the game and exclude miners and their enormous waste of power energy. Thus, the purpose of this paper is to show that even a piece of paper can be recycled into a secure Ecash, while remaining environmentally friendly. Hence, we create here a cryptocurrency that would use a slight modification of the current banknotes to set up anonymous electronic transactions. By trading with banknotes, we mechanically transfer ownership of the paper money from one owner to another, hence, in this scheme, we introduce the notion of ownership transfer. It implies that at each transaction the elements allowing to authenticate the Ecash does not change, while the ownership certificate will change since the Ecash is transfer towards someone else.

Marcella Atzori

Although the blockchain is widely acknowledged as one of the most disruptive technologies emerged in the last decades, many implementation hurdles at the technical, regulatory and governance level still prevent a widespread adoption of services based on open networks. This research discusses the role Trust Service Providers may play in permissioned blockchains, providing a reliable ecosystem in which services can be safely developed and preserved in the long run. As case study, the paper outlines the main features of TrustedChain®, the first blockchain network of European Trust Service Providers specifically designed for highly sensitive sectors, with cutting-edge applications for public administration, e-government, banking, e-health and industry. Emphasis is thus placed on systemic trust, law compliance, adequate technical performance, confidentiality of transactions and long term preservation of data as essential conditions for blockchain networks to thrive and accomplish complex tasks in an effective and reliable way.

Chien-Nan Wu, Chun‐I Fan, Jheng-Jia Huang, Yi‐Fan Tseng · 5 authors

This article describes how after the concept of anonymous credential systems was introduced in 1985, a number of similar systems have been proposed. However, these systems use zero-knowledge protocols to authenticate users, resulting in inefficient authentication during the stage of proving credential possession. To overcome this drawback, this article presents a signature scheme that uses partially blind signatures and chameleon hash functions such that both the prover and verifier achieve efficient authentication. In addition to providing a computational cost comparison table showing that the proposed signature scheme achieves a more efficient credential possession proving compared to other schemes, concrete security proofs are provided under a random oracle model to demonstrate that the proposed scheme satisfies the properties of anonymous credentials.

Xunhua Wang, Brett Tjaden, Mohammad Heydari

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Roberto Di Pietro, Xavier Salleras, Matteo Signorini, Erez Waisbard

One of the biggest challenges for the Internet of Things (IoT) is to bridge the currently fragmented trust domains. The traditional PKI model relies on a common root of trust and does not fit well with the heterogeneous IoT ecosystem where constrained devices belong to independent administrative domains. In this work we describe a distributed trust model for the IoT that leverages the existing trust domains and bridges them to create end-to-end trust between IoT devices without relying on any common root of trust. Furthermore we define a new cryptographic primitive, denoted as obligation chain designed as a credit-based Blockchain with a built-in reputation mechanism. Its innovative design enables a wide range of use cases and business models that are simply not possible with current Blockchain-based solutions while not experiencing traditional blockchain delays. We provide a security analysis for both the obligation chain and the overall architecture and provide experimental tests that show its viability and quality.

Quinten Stokkink, Johan Pouwelse

Digital identity is unsolved: after many years of research there is still no trusted communication over the Internet. To provide identity within the context of mutual distrust, this paper presents a blockchain-based digital identity solution. Without depending upon a single trusted third party, the proposed solution achieves passport-level legally valid identity. This solution for making identities Self-Sovereign, builds on a generic provable claim model for which attestations of truth from third parties need to be collected. The claim model is then shown to be both blockchain structure and proof method agnostic. Four different implementations in support of these two claim model properties are shown to offer sub-second performance for claim creation and claim verification. Through the properties of Self-Sovereign Identity, legally valid status and acceptable performance, our solution is considered to be fit for adoption by the general public.

Joshua Lind, Oded Naor, Ittay Eyal, Florian Kelbert · 6 authors

Blockchains such as Bitcoin and Ethereum execute payment transactions securely, but their performance is limited by the need for global consensus. Payment networks overcome this limitation through off-chain transactions. Instead of writing to the blockchain for each transaction, they only settle the final payment balances with the underlying blockchain. When executing off-chain transactions in current payment networks, parties must access the blockchain within bounded time to detect misbehaving parties that deviate from the protocol. This opens a window for attacks in which a malicious party can steal funds by deliberately delaying other parties' blockchain access and prevents parties from using payment networks when disconnected from the blockchain.

Beini Zhou, Hui Li, Li Da Xu

Identity-based encryption is a key distribution system in which the public key of a user is derived directly from his identity information. Compared with PKI, Identity-based encryption simplifies key management issue, but it still suffers from drawbacks inkey escrow and private key delivering. Motivated by this, we propose an improved key distribution solution called BIBE by integrating the technique of blockchain into the identity-based encryption. Specifically, we split the nodes in the chain to complete user authentication and private key protection, respectively. Furthermore, the two sides complete the mutual identity authentication with the identity information key pairs obtained from BIBE. Additionally, to prevent network attack, we employ timestamps, random numbers and hash algorithm in the process of identification. Through the rigorous and mathematical analysis, the proposed scheme demonstratesa far better performance on correctness, safety and efficiency.

Siye Wang, Shaoyi Zhu, Yanfang Zhang

Since radio frequency identification (RFID) technology has been used in various scenarios such as supply chain, access control system and credit card, tremendous efforts have been made to improve the authentication between tags and readers to prevent potential attacks. Though effective in certain circumstances, these existing methods usually require a server to maintain a database of identity related information for every tag, which makes the system vulnerable to the SQL injection attack and not suitable for distributed environment. To address these problems, we now propose a novel blockchain-based mutual authentication security protocol. In this new scheme, there is no need for the trusted third parties to provide security and privacy for the system. Authentication is executed as an unmodifiable transaction based on blockchain rather than database, which applies to distributed RFID systems with high security demand and relatively low real-time requirement. Analysis shows that our protocol is logically correct and can prevent multiple attacks.

Tam Le, Matt W. Mutka

Devices to support pervasive computing and the Internet of Things (IoT) are becoming present in almost every aspect of our lives. Due to their limited power and computation, these devices often need to rely on some more powerful outsourced cloud services, which raises a security and privacy concern as IoT data is often sensitive. On the other hand, blockchain technology has recently gained much attention due to its decentralized, trustless and immutable design. We propose CapChain - an access control framework based on blockchain that allows users to share and delegate their access rights easily to IoT devices in public but still maintain privacy. To protect privacy, we adapt multiple techniques from anonymous crypto-currency blockchain systems to hide sensitive information, including users' identities and related information about the capabilities. We also build a testbed as a proof of concept.

Michal Zima

Bitcoin blockchain is growing big, yet its transaction capacity hit its limits in 2017. One solution heavily discussed within the bitcoin community is to let it grow faster by increasing size of the blocks. However, making transactions smaller instead of blocks bigger is more sustainable and also brings other additional benefits. In this paper, we focus on space wasted by non-cryptographic use of hashes and uncompressed numbers within transaction inputs. In our analyses, we show that transactions can be made approximately 16% smaller, depending on their complexity.

Nachiket Tapas, Giovanni Merlino, Francesco Longo

In a Smart City scenario, the authors envisioned an IoT-Cloud framework for the management of boards and resources scattered over a geographic area. It can also become a tool to let device owners contribute freely to the infrastructure. In comparison to datacenter-oriented Cloud middleware, the administrator and the owner of the infrastructure are not one and the same. This translates into the requirement to support delegation-enabled authorization. In this paper, the authors investigate an authorization and delegation model for the IoT-Cloud based on blockchain technology. In particular, the scheme is implemented in the form of smart contracts over the Ethereum platform. Indeed, this approach represents an enhancement, over a function previously designed in a centralized fashion, by enabling the user to audit authorization operations and inspect how access control is actually performed, without blindly trusting the Cloud as a proxy for access to resources.

Wentong Wang, Ning Hu, Xin Liu

In a distributed network environment, companies and institutions have their own sharing resource. To prevent unauthorized users to access these shared resources, cross-domain authentication is necessary. For ensuring the safety and efficiency to access resources in different domain, we propose a blockchain-based cross-domain authentication model called BlockCAM and designed the cross-domain authentication protocol. BlockCAM employs consortium blockchain technology to construct a decentralized network with the root Certificate Authorities as the verification nodes. The hash values of the authorized certificates are stored in each block and the verification process only needs to compare whether the hash calculated by the certificate provided by the user is consistent with the hash stored in the blockchain. The authentication process omits the key encryption and decryption overhead. BlockCAM has the characteristics of decentralization, anonymity and temper-resistant. Analyses show that BlockCAM has the advantage over the existing public key infrastructure (PKI) cross-domain authentication schemes at efficiency.

He Simeng, Chao Yang, Qi Jiang, Yang Li · 5 authors

No abstract is available for this record.

Rafaël del Pino

Preuves à divulgation nulle de connaissance efficaces à base de réseaux euclidiens et applications Le chiffrement à base de réseaux euclidiens a connu un grand essor durant les vingt dernières années. Autant grâce à l’apparition de nouvelles primitives telles que le chiffrement complètement homomorphe, que grâce à l’amélioration des primitives existantes, comme le chiffrement á clef publique ou les signatures digitales, qui commencent désormais à rivaliser avec leurs homologues fondés sur la théorie des nombres. Cela dit les preuves à divulgation nulle de connaissance, bien qu’elles représentent un des piliers des protocols de confidentialité, n’ont pas autant progressé, que ce soit au niveau de leur expressivité que de leur efficacité. Cette thèse s’attelle dans un premier temps à améliorer l’état de l’art en matière de preuves à divulgation nulle de connaissance. Nous construisons une preuve d’appartenance à un sous ensemble dont la taille est indépendante de l’ensemble en question. Nous construisons de même une preuve de connaissance amortie qui est plus efficace et plus simple que toutes les constructions qui la précèdent. Notre second propos est d’utiliser ces preuves à divulgation nulle de connaissance pour construire de nouvelles primitives cryptographiques. Nous concevons une signature de groupe dont la taille est indépendante du groupe en question, ainsi qu’un schéma de vote électronique hautement efficace, y compris pour des élections à grand échelle.

Bogdan Florea

This paper describes the use of blockchain technology as a data provider in Internet of Things (IoT) applications. Blockchain is a novel technology, which has gained a lot of attention in the last years, mainly due to its use as a backbone for cryptocurrencies. The main purpose of blockchain technology is to provide anonymous transactions between participants, over a peer-to-peer network, using a decentralized distributed ledger. The goal of this novel approach is to eliminate any 3rdparty validation and replace the trust of a central authority for transaction validation with cryptographic proof. While most applications of the blockchain revolve around cryptocurrencies, the blockchain can be used in many other fields, such as finance, distributed data storage, health and medicine, automation, etc. By creating an open, decentralized network, the blockchain can be used to develop decentralized applications and enable data access and sharing on a much higher level than the common implementations of client-server architectures which are in use today. In this paper, we will present a proof of concept method for field devices to store and share data using a distributed ledger built on the IOTA tangle, as well as provide means of access to the data which can be used in IoT and decentralized applications.

Ravi Kiran Raman, Lav R. Varshney

Blockchain uses the idea of storing transaction data in the form of a distributed ledger wherein each node in the network stores a current copy of the sequence of transactions (ledger) in the form of a hash chain. Storing the entire ledger incurs a high storage cost that grows undesirably large for high transaction rates and large networks. In this work we use secret key sharing, private key encryption, and distributed storage to design a coding scheme such that each node stores only a part of each transaction thereby reducing storage cost to a fraction of the original. When further using dynamic zone allocation, we show the coding scheme can also improve the data integrity.

Lin Chen, Lei Xu, Zhimin Gao, Yang Lü · 5 authors

Proof-of-work was originally proposed by Dwork and Naor in 1992 and has proved its powerfulness in Bitcoin as a decentralized mechanism for blockchain construction. Proof-of-work is the basis of most popular cryptocurrencies and smart contract systems, where participating miners are required to solve difficult mathematical problems to validate transactions. One of the major challenges that proof-of-work faces is the 51% attack, i.e., if an adversary controls more than half of the computation power, he/she can control the blockchain construction and determine which blocks will be included. This is not a major concern when the number of miners is large. However, for an early stage blockchain system with a limited number of users, it is relatively easy for an attacker to launch the 51% attack. To mitigate such risk, we propose a new hybrid blockchain construction scheme that uses the combination of proof-of-work and the stake, which is the number of coins produced by a miner, to determine whether this miner is allowed to construct a block. We prove that stakes play an important role in the hybrid scheme at the beginning, so that an attacker is not able to launch the 51% attack even if he/she controls the majority of the computational power. Meanwhile, the hybrid scheme will converge to pure proof-of-work after sufficiently many blocks are generated, and thus captures the desired properties of proof-of-work. Most importantly, such a convergence is "smooth" in the sense that neither changes in the rules nor parameters are introduced, and thus no hard/soft-forks will be triggered. We also demonstrate the effectiveness of the new scheme using simulations with different configurations, which can help a designer to select adequate parameters for a specific blockchain application.

Kazım Rıfat Özyılmaz, Mehmet Ug̃ur Dog̃an, Arda Yurdakul

Today, Internet of Things (IoT) devices are the powerhouse of data generation with their ever-increasing numbers and widespread penetration. Similarly, artificial intelligence (AI) and machine learning (ML) solutions are getting integrated to all kinds of services, making products significantly more "smarter". The centerpiece of these technologies is "data". IoT device vendors should be able keep up with the increased throughput and come up with new business models. On the other hand, AI/ML solutions will produce better results if training data is diverse and plentiful. In this paper, we propose a blockchain-based, decentralized and trustless data marketplace where IoT device vendors and AI/ML solution providers may interact and collaborate. By facilitating a transparent data exchange platform, access to consented data will be democratized and the variety of services targeting end-users will increase. Proposed data marketplace is implemented as a smart contract on Ethereum blockchain and Swarm is used as the distributed storage platform.

Rodelio Arenas, Proceso Fernandez

Blockchain, the underlying technology that powers cryptocurrencies such as Bitcoin and Ethereum, is gaining so much attention from different industry stakeholders, governments and research communities. Its application is extending beyond cryptocurrencies and has been exploited in different domains such as finance, E-commerce, Internet of Things (IoT), healthcare, and governance. Some key attributes of the technology are decentralization, immutability, security and transparency. This paper aims to describe how permissioned Blockchain can be applied to a specific educational use case - decentralized verification of academic credentials. The proposed Blockchain-based solution, named `CredenceLedger', is a system that stores compact data proofs of digital academic credentials in Blockchain ledger that are easily verifiable for education stakeholders and interested third party organizations.

Iain Stewart, Dragos Ilie, Alexei Zamyatin, Sam M. Werner · 6 authors

Quantum computers are expected to have a dramatic impact on numerous fields due to their anticipated ability to solve classes of mathematical problems much more efficiently than their classical counterparts. This particularly applies to domains involving integer factorization and discrete logarithms, such as public key cryptography. In this paper, we consider the threats a quantum-capable adversary could impose on Bitcoin, which currently uses the Elliptic Curve Digital Signature Algorithm (ECDSA) to sign transactions. We then propose a simple but slow commit-delay-reveal protocol, which allows users to securely move their funds from old (non-quantum-resistant) outputs to those adhering to a quantum-resistant digital signature scheme. The transition protocol functions even if ECDSA has already been compromised. While our scheme requires modifications to the Bitcoin protocol, these can be implemented as a soft fork.

Peter Gaži, Aggelos Kiayias, Alexander Russell

We describe a general attack on proof-of-stake (PoS) blockchains without checkpointing. Our attack leverages transaction fees, the ability to treat transactions "out of context," and the standard longest chain rule to completely dominate a blockchain. The attack grows in power with the number of honest transactions and the stake held by the adversary, and can be launched by an adversary controlling any constant fraction of the stake. With the present statistical profile of blockchain protocols, the attack can be launched given a few years of prior blockchain operation; hence it is within the realm of feasibility for PoS protocols. Most importantly, it demonstrates how closely transaction fees and rewards are coupled with the security properties of PoS protocols. More broadly, our attack must be reflected and countered in any future PoS design that avoids checkpointing, as well as any effort to remove checkpointing from existing protocols. We describe several mechanisms for protecting against the attack that include context-sensitivity of transactions and chain density statistics.