In December 2015, a bounty emerged to establish both reliable communication and secure transfer of value between the Dogecoin and Ethereum blockchains. This prized "Dogethereum bridge" would allow parties to "lock" a DOGE coin on Dogecoin and in exchange receive a newly minted WOW token in Ethereum. Any subsequent owner of the WOW token could burn it and, in exchange, earn the right to "unlock" a DOGE on Dogecoin. We describe an efficient, trustless, and retrofitting Dogethereum construction which requires no fork but rather employs economic collateral to achieve a "lock" operation in Dogecoin. The protocol relies on bulletproofs, Truebit, and parametrized tokens to efficiently and trustlessly relay events from the "true" Dogecoin blockchain into Ethereum. The present construction not only enables cross-platform exchange but also allows Ethereum smart contracts to trustlessly access Dogecoin. A similar technique adds Ethereum-based smart contracts to Bitcoin and Bitcoin data to Ethereum smart contracts.
The Cloud Computing Paradigm simplified the IT infrastructure management thereby making the organiza-tions and enterprises to rapidly migrate from conventional model to service driven model. The service driven model allows the users to access, maintain and backup the files from remote location over the internet through the central-ized cloud service providers. Inspite of major advantages, there are some concerns for the safety and privacy risks of organizational and users sensitive information in cloud stor-age. The existing service oriented model uses distributed key management which encrypts the data and stores it in cloud servers to provide the authentication to data, but it addresses challenges in identifying ownership of data, boot-strapping problem and securing the keys. The proposed system uses block chain, a distributed ledger for user authentication in cloud server and Hash graph with asynchronous byzantine fault tolerance algorithm is proposed for replicat-ed state machines with guaranteed Byzantine fault-tolerance and it can be utilized in the IT Infrastructure envi-ronment which solves the hassles of maintaining security keys
Recent advances in the cryptographic field of "Zero-Knowledge Proofs" have sparked a new wave of research, giving birth to many exciting theoretical approaches in the last few years. Such research has often overlapped with the need for private and scalable solutions of Blockchain-based communities, resulting in the first practical implementations of such systems. Many of these innovative constructions have developed in parallel, using different terminologies and evolving into a fragmented ecosystem, calling for their consolidation into the more stable domain of "Verifiable Computation". In this master thesis I propose a unifying Verifiable Computation model for the simplification and efficient comparison of all cryptographic proof systems. I take advantage of this model to analyse innovative technologies (Homomorphic Authenticators, Verifiable Delay Functions) which developed into their own specialised domains, and I attempt to make them more accessible for newcomers to the field. Furthermore, I expand on the future of Verifiable Computation, Universal proof compilers and "Proofs of All", by approaching the state-of-the-art zk-STARK construction from a more accessible and informal design perspective.
Davide Frey, Marc X. Makkes, Pierre-Louis Roman, François Taı̈ani · 5 authors
Distributed ledgers are among the most replicated data repositories in the world. They offer data consistency, immutability, and auditability, based on the assumption that each participating node locally verifies their entire content. Although their content, currently extending up to a few hundred gigabytes, can be accommodated by dedicated commodity hard disks, downloading it, processing it, and storing it in general-purpose desktop and laptop computers can prove largely impractical. Even worse, this becomes a prohibitive restriction for smartphones, mobile devices, and resource-constrained IoT devices. In this demo, we present an implementation of Dietcoin, a Bitcoin protocol extension that allows nodes to perform secure local verification of Bitcoin transactions with small bandwidth and storage requirements. This demo presents and benchmarks the main features of Dietcoin that are important for today's cryptocurrencies and smart contract systems, but are missing in the current state-of-the-art: (i) allowing resource-constrained devices to verify the correctness of selected blocks locally without having to download the complete ledger; (ii) enabling devices to join a blockchain quickly yet securely, dropping bootstrap time from days down to a matter of seconds; (iii) providing a generic solution that can be applied to other distributed ledgers secured with Proof-of-Work.
Santiago Figueroa-Lorenzo, Javier Añorga, Saioa Arrizabalaga
The growing adoption of Radio-frequency Identification (RFID) systems, particularly in the healthcare field, demonstrates that RFID is a positive asset for healthcare institutions. RFID offers the ability to save organizations time and costs by enabling data of traceability, identification, communication, temperature and location in real time for both people and resources. However, the RFID systems challenges are financial, technical, organizational and above all privacy and security. For this reason, recent works focus on attribute-based access control (ABAC) schemes. Currently, ABAC are based on mostly centralized models, which in environments such as the supply chain can present problems of scalability, synchronization and trust between the parties. In this manuscript, we implement an ABAC model in RFID systems based on a decentralized model such as blockchain. Common criteria for the selection of the appropriate blockchain are detailed. Our access control policies are executed through the decentralized application (DApp), which interfaces with the blockchain through the smart contract. Smart contracts and blockchain technology, on the one hand, solve current centralized systems issues as well as being flexible infrastructures that represent the relationship of trust and support essential in the ABAC model in order to provide the security of RFID systems. Our system has been designed for a supply chain environment with an use case suitable for healthcare systems, so that assets such as surgical instruments containing an associated RFID tag can only access to specific areas. Our system is deployed in both a local and Testnet environment in order to stablish a deep comparison and determining the technical feasibility.
Emmanuelle Anceaume, Marina Papatriantafilou, Maria Potop-Butucaru, Philippas Tsigas
This paper continues the recent line of academic effort dedicated to formalizing distributed ledgers. This work is the first one to propose a specification of distributed ledger register that matches the Lamport hierarchy from safe to atomic. Moreover, we propose implementations of distributed ledger registers with safe, regular and atomic guaranties in a model of communication specific to distributed ledgers technology that we also formalize. Then, we propose an implementation of a distributed ledger register that satisfies the atomic specification and the k-consistency property that characterises the permissionless distributed blockchains such as Bitcoin and Ethereum.
Ghareeb Falazi, Vikas Khinchi, Uwe Breitenbücher, Frank Leymann
Traditional distributed transaction processing (TP) systems, such as replicated databases, faced difficulties in getting wide adoption for scenarios of enterprise integration due to the level of mutual trust required. Ironically, public blockchains, which promised to solve the problem of mutual trust in collaborative processes, suffer from issues like scalability, probabilistic transaction finality, and lack of data confidentiality. To tackle these issues, permissioned blockchains were introduced as an alternative approach combining the positives of the two worlds and avoiding their drawbacks. However, no sufficient analysis has been done to emphasize their actual capabilities regarding TP. In this paper, we identify a suitable collection of TP criteria to analyze permissioned blockchains and apply them to a prominent set of these systems. Finally, we compare the derived properties and provide general conclusions.
Danil Annenkov, Jakob Botsch Nielsen, Bas Spitters
We present a new way of embedding functional languages into the Coq proof assistant by using meta-programming. This allows us to develop the meta-theory of the language using the deep embedding and provides a convenient way for reasoning about concrete programs using the shallow embedding. We connect the deep and the shallow embeddings by a soundness theorem. As an instance of our approach, we develop an embedding of a core smart contract language into Coq and verify several important properties of a crowdfunding contract based on a previous formalisation of smart contract execution in blockchains.
The Ethereum blockchain is essentially a globally replicated public database.\nPrograms called smart contracts can access this database. Over 10 million smart\ncontracts have been deployed on the Ethereum blockchain. Executing a method of\na smart contract generates a transaction that is also stored on the blockchain.\nThere are over 1 billion Ethereum transactions to date. Smart contracts that\nare transparent about their function are more successful than opaque contracts.\nWe have therefore developed a tool (ContractVis) to explore the transparency of\nsmart contracts. The tool generates a replay script for the historic\ntransactions of a smart contract. The script executes the transactions with the\nsame arguments as recorded on the blockchain, but in a minimal test\nenvironment. Running a replay script provides insights into the contract, and\ninsights into the blockchain explorer that was used to retrieve the contract\nand its history. We provide five concrete recommendations for blockchain\nexplorers like Etherscan to improve the transparency of smart contracts.\n
Open access
3 source records
Blockchain Technology Applications and Security
Auction Theory and Applications
Advanced Steganography and Watermarking Techniques
Eugenia Politou, Fran Casino, Efthimios Alepis, Constantinos Patsakis
Abstract—Blockchain’s evolution during the past decade is astonishing: from bitcoin to over 2.000 altcoins, and from decentralised electronic payments to transactions programmable by smart contracts and complex tokens governed bydecentralised organisations. While the new generation of blockchain appli- cations is still evolving, blockchain’s technical characteristics are also advancing. Yet, immutability, a hitherto indisputable property according to which blockchain data cannot be edited nor deleted, remains the cornerstone of blockchain’s security. Nevertheless, blockchain’s immutability is being called into ques- tion lately in the light of the new erasing requirements imposed by the GDPR’s “Right to be Forgotten (RtbF)” provision. As the RtbF obliges blockchain data to be editable in order restricted content redactions, modifications or deletions to be applied when requested, blockchains compliance with the regulation is indeed challenging, if not impracticable. Towards resolving this contradiction, various methods and techniques for mutable blockchains have been proposed in an effort to satisfy regulatory erasing requirements while preserving blockchains’ security. To this end, this work aims to provide a comprehensive review on the state-of-the-art research approaches, technical workarounds and advanced cryptographic techniques that have been put forward to resolve this conflict and to discuss their potentials, constraints and limitations when applied in the wild to either permissioned or permissionless blockchains. Index Terms—Blockchain, immutability, Right to be forgotten, GDPR
Abhinav Aggarwal, Mahnush Movahedi, Jared Saia, Mahdi Zamani
We propose a protocol that allows the participants of a permissionless decentralized system to agree on a set of identities in the presence of a computationally-bounded Byzantine adversary. Our protocol guarantees that the fraction of identities belonging to the adversary in the set of identities is at most equal to the total computational hash power of the adversary.
Eduardo Morais, Tommy Koens, Cees van Wijk, Aleksei Koren
In last years, there has been an increasing effort to leverage Distributed Ledger Technology (DLT), including blockchain. One of the main topics of interest, given its importance, is the research and development of privacy mechanisms, as for example is the case of Zero Knowledge Proofs (ZKP). ZKP is a cryptographic technique that can be used to hide information that is put into the ledger, while still allowing to perform validation of this data. In this work we describe different strategies to construct Zero Knowledge Range Proofs (ZKRP), as for example the scheme proposed by Boudot in 2001; the one proposed in 2008 by Camenisch et al, and Bulletproofs, proposed in 2017. We also compare these strategies and discuss possible use cases. Since Bulletproofs is the most efficient construction, we will give a detailed description of its algorithms and optimizations. Bulletproofs is not only more efficient than previous schemes, but also avoids the trusted setup, which is a requirement that is not desirable in the context of Distributed Ledger Technology (DLT) and blockchain. In case of cryptocurrencies, if the setup phase is compromised, it would be possible to generate money out of thin air. Interestingly, Bulletproofs can also be used to construct generic Zero Knowledge Proofs (ZKP), in the sense that it can be used to prove generic statements, and thus it is not only restricted to ZKRP, but it can be used for any kind of Proof of Knowledge (PoK). Hence Bulletproofs leads to a more powerful tool to provide privacy for DLT. Here we describe in detail the algorithms involved in Bulletproofs protocol for ZKRP. Also, we present our implementation, which was open sourced.
The Internet of things (IoT) presents new opportunities and challenges due to its scale and dynamic nature. One significant challenge for the IoT is the need for security, in particular access control solutions, that are designed to meet the characteristics of these systems. Delegation of rights, from one entity to another, is a crucial component of an access control system. The IoT requires a secure, flexible, and fine-grained delegation model. While there has been considerable work in the area of delegation, much of it assumes a centralized, well-resourced system and these solutions have limited capacity in the context of the IoT. Where delegation models for the IoT have been proposed they typically provide only coarse-grained control over the delegation of rights. Moreover, many of them require a centralized trusted authority, which can suffer from a single-point failure and is not an ideal base for a large and dynamic system like the IoT. In this paper, we propose an identity-less, asynchronous, and decentralized delegation model for the IoT based on blockchain technology. We describe system components, architecture, and key aspects related to the security of the system. We use attributes to validate an entity rather than depending upon unique identities. We demonstrate the feasibility of our model through use-case examples and analyze the performance with a proof of concept testbed implementation using Ethereum private blockchain.
Devrim Ünal, Mohammad Hammoudeh, Mehmet Sabır Kiraz
Blockchain offers unprecedented opportunities for innovation in financial transactions. A whole new world of opportunities for banking, lending, insurance, money transfer, investments, and stock markets awaits. However, the potential for wide-scale adoption of blockchain is hindered with cybersecurity and privacy issues. We provide an overview of the risks and security requirements and give an outlook for future research that could be helpful in solving some of the challenges. We also present an approach for policy specification and verification of financial transactions based on smart contracts.
Bitcoin is a peer-to-peer payment system proposed by Nakamoto in 2008. Properties of the bitcoin backbone protocol have been investigated in some depth: the blockchain growth property quantifies the number of blocks added to the blockchain during any time intervals; the blockchain quality property ensures the honest miners always contribute at least a certain fraction of the blockchain; the common prefix property ensures if a block is deep enough, it will eventually be adopted by all honest miners with high probability. Following the spirit of decoupling various functionalities of the blockchain, the Prism protocol is proposed to dramatically improve the throughput while maintaining the same level of security. Prior analyses of the bitcoin and Prism backbone protocols assume the lifespan of blockchain is finite. This paper presents a streamlined and strengthened analysis without the finite horizon assumption. Specifically, the results include a blockchain growth property, a blockchain quality property, and a common prefix property of the bitcoin backbone protocol, as well as the liveness and persistence of the Prism backbone protocol regardless of whether the blockchains have a infinite lifespan. We also express the properties of bitcoin and Prism backbone protocols in explicit expressions rather than order optimal results, which lead to tighter bounds and practical references for public transaction ledger protocol design.
Antoine Durand, Emmanuelle Anceaume, Romaric Ludinard
Our work focuses on the design of a scalable permissionless blockchain in the\nproof-of-stake setting. In particular, we use a distributed hash table as a\nbuilding block to set up randomized shards, and then leverage the sharded\narchitecture to validate blocks in an efficient manner. We combine verifiable\nByzantine agreements run by shards of stakeholders and a block validation\nprotocol to guarantee that forks occur with negligible probability. We impose\ninduced churn to make shards robust to eclipse attacks, and we rely on the UTXO\ncoin model to guarantee that any stakeholder action is securely verifiable by\nanyone. Our protocol works against adaptive adversary, and makes no synchrony\nassumption beyond what is required for the byzantine agreement.\n
IOTA opened recently a new line of research in distributed ledgers area by targeting algorithms that ensure a high throughput for the transactions generated in IoT systems. Transactions are continuously appended to an acyclic structure called tangle and each new transaction selects as parents two existing transactions (called tips) that it approves. G-IOTA, a very recent improvement of IOTA, targets to protect tips left behind offering hence a good confidence level. However, this improvement had a cost: the use of an additional tip selection mechanism which may be critical in IoT systems since it needs additional energy consumption. In this paper we propose a new metamorphic algorithm for tip selection that offers the best guaranties of both IOTA and G-IOTA. Our contribution is two fold. First, we propose a parameterized algorithm, E-IOTA, for tip selection which targets to reduce the number of random walks executed in previous versions (IOTA and G-IOTA) while maintaining the same security guaranties as IOTA and the same confidence level and fairness with respect to tips selection as G-IOTA. Then we propose a formal analysis of the security guaranties offered by E-IOTA against various attacks mentioned in the original IOTA proposal (e.g. large weight attack, parasite chain attack and splitting attack). Interestingly, to the best of our knowledge this is the first formal analysis of the security guaranties of IOTA and its derivatives.
In this paper, we propose a system for mixing transactions in payment networks such as credit networks. Credit networks like Ripple and Stellar are increasingly popular, and can facilitate crosscurrency transactions in a fraction of the time it would take for banks or other financial institutions to process the same transaction, and at a fraction of the cost. Unlike for cryptocurrencies, there has been little work in the area of designing secure and private mixers for credit networks. Mixers for cryptocurrencies such as Bitcoin cannot be directly applied to the credit network domain because credit networks have an inherently different structure and purpose than cryptocurrencies. We design a system that uses cryptographic constructs such as ring signatures, commitments, and zero knowledge proofs to provide security/integrity of all transactions, ensures privacy of the users involved in a transaction, as well as privacy of the amount transacted. We also provide preliminary experimental results.
We study the relationship between problems solvable by quantum algorithms in polynomial time and those for which zero-knowledge proofs exist. In prior work, Aaronson [arxiv:quant-ph/0111102] showed an oracle separation between BQP and SZK, i.e. an oracle $A$ such that $\mathrm{SZK}^A \not\subseteq \mathrm{BQP}^A$. In this paper we give a simple extension of Aaronson's result to non-interactive zero-knowledge proofs with perfect security. This class, NIPZK, is the most restrictive zero-knowledge class. We show that even for this class we can construct an $A$ with $\mathrm{NIPZK}^A \not\subseteq \mathrm{BQP}^A$.
We study the relationship between problems solvable by quantum algorithms in\npolynomial time and those for which zero-knowledge proofs exist. In prior work,\nAaronson [arxiv:quant-ph/0111102] showed an oracle separation between BQP and\nSZK, i.e. an oracle $A$ such that $\\mathrm{SZK}^A \\not\\subseteq\n\\mathrm{BQP}^A$. In this paper we give a simple extension of Aaronson's result\nto non-interactive zero-knowledge proofs with perfect security. This class,\nNIPZK, is the most restrictive zero-knowledge class. We show that even for this\nclass we can construct an $A$ with $\\mathrm{NIPZK}^A \\not\\subseteq\n\\mathrm{BQP}^A$.\n
Quan Nguyen, André Cronje, Michael Kong, Alex Kampa · 5 authors
Trustless systems, such as those blockchain enpowered, provide trust in the system regardless of the trust of its participants, who may be honest or malicious. Proof-of-stake (PoS) protocols and DAG-based approaches have emerged as a better alternative than the proof of work (PoW) for consensus. This paper introduces a new model, so-called \emph{\stakedag}, which aims for PoS consensus in a DAG-based trustless system. We address a general model of trustless system in which participants are distinguished by their stake or trust: users and validators. Users are normal participants with a no assumed trust and validators are high profile participants with an established trust. We then propose a new family of stake-based consensus protocols $\mathfrak{S}$, operating on the DAG as in the Lachesis protocol~\cite{lachesis01}. Specifically, we propose a stake-based protocol $S_φ$ that leverages participants' stake as validating weights to achieve more secure distributed systems with practical Byzantine fault tolerance (pBFT) in leaderless asynchronous Directed Acyclic Graph (DAG). We then present a general model of staking for asynchronous DAG-based distributed systems.
Abstract A major line of research on blockchains is geared towards enhancing the privacy of transactions through anonymity using generic non-interactive proofs. However, there is a good cluster of application scenarios where complete anonymity is not desirable and accountability is in fact required. In this work, we utilize non-interactive proofs of knowledge of elliptic curve discrete logarithms to present membership and verifiable encryption proof, which offers plausible anonymity when combined with the regular signing process of the blockchain transactions. The proof system requires no trusted setup, both its communication and computation complexities are linear in the number of set members, and its security relies on the discrete logarithm assumption. As a use-case for this scenario, we present Mesh which is a blockchain-based framework for supply chain management using RFIDs. Finally, the confidentiality of the transacted information is realized using a lightweight key chaining mechanism implemented on RFIDs. We formally define and prove the main security features of the protocol, and report on experiments for evaluating the performance of the modified transactions for this system.
Open access
Cryptography and Data Security
Blockchain Technology Applications and Security
Advanced Steganography and Watermarking Techniques
Michael N. Jones, Matthew Johnson, Mark Shervey, Joel T. Dudley · 5 authors
BACKGROUND: The protection of private data is a key responsibility for research studies that collect identifiable information from study participants. Limiting the scope of data collection and preventing secondary use of the data are effective strategies for managing these risks. An ideal framework for data collection would incorporate feature engineering, a process where secondary features are derived from sensitive raw data in a secure environment without a trusted third party. OBJECTIVE: This study aimed to compare current approaches based on how they maintain data privacy and the practicality of their implementations. These approaches include traditional approaches that rely on trusted third parties, and cryptographic, secure hardware, and blockchain-based techniques. METHODS: A set of properties were defined for evaluating each approach. A qualitative comparison was presented based on these properties. The evaluation of each approach was framed with a use case of sharing geolocation data for biomedical research. RESULTS: We found that approaches that rely on a trusted third party for preserving participant privacy do not provide sufficiently strong guarantees that sensitive data will not be exposed in modern data ecosystems. Cryptographic techniques incorporate strong privacy-preserving paradigms but are appropriate only for select use cases or are currently limited because of computational complexity. Blockchain smart contracts alone are insufficient to provide data privacy because transactional data are public. Trusted execution environments (TEEs) may have hardware vulnerabilities and lack visibility into how data are processed. Hybrid approaches combining blockchain and cryptographic techniques or blockchain and TEEs provide promising frameworks for privacy preservation. For reference, we provide a software implementation where users can privately share features of their geolocation data using the hybrid approach combining blockchain with TEEs as a supplement. CONCLUSIONS: Blockchain technology and smart contracts enable the development of new privacy-preserving feature engineering methods by obviating dependence on trusted parties and providing immutable, auditable data processing workflows. The overlap between blockchain and cryptographic techniques or blockchain and secure hardware technologies are promising fields for addressing important data privacy needs. Hybrid blockchain and TEE frameworks currently provide practical tools for implementing experimental privacy-preserving applications.
Samvid Dharanikota, Michael Jensen, Sebastian Rom Kristensen, Mathias Sass Michno · 7 authors
Randomness beacons are services that periodically emit a random number, allowing users to base decisions on the same random value without trusting anyone: ideally, the randomness beacon does not only produce unpredictable values, but is also of low computational complexity for the users, bias-resistant and publicly verifiable. Such randomness beacons can serve as an important primitive for smart contracts in a variety of contexts. This paper first presents a structured security analysis, based on which we then design, implement, and evaluate a trustworthy and efficient randomness beacon. Our approach does not require users to register or run any computationally intensive operations. We then compare different implementation and deployment options on distributed ledgers, and report on an Ethereum smart contract-based lottery using our beacon.