Tom Godden, Ruben De Smet, Christophe Debruyne, Thibaut Vandervelden · 6 authors
Driven by the increased consciousness in data ownership and privacy, zero-knowledge proofs (ZKPs) have become a popular tool to convince a third party of the truthfulness of a statement without disclosing any further information. As ZKPs are rather complex to design, frameworks that transform high-level languages into ZKPs have been proposed. We propose Circuitree, a Datalog reasoner in zero-knowledge. Datalog is a high-level declarative logic language that is generally used for querying. Furthermore, as a logic language, it can also be used to solve logic problems. An application using Circuitree can efficiently generate ZKPs, based on Datalog rules and encrypted data, to prove that a certain conclusion follows from a Datalog ruleset and encrypted input data. Compared to existing frameworks, which generally use their own limited imperative languages, Circuitree uses an existing high-level declarative language. We point out several applications for Circuitree, including EU Digital COVID Certificates and privacy-preserving access control for peer-to-peer (p2p) networks. Circuitree’s performance is evaluated for access control in a p2p network. First results show that our approach allows for fast proofs and proof verification for this application.
The decentralization feature of public and private blockchain-based applications is achieved by selecting different nodes as validator or Certificate Authority (CA) for each transaction. Public blockchain uses Proof of Work (PoW) to search for the validator. PoW causes an enormous amount of energy. Therefore, Proof of Stake (PoS), and Proof of Authority (PoA) emerged as alternate solutions. Selection of a newCAusingPoSorPoAalgorithms for each transaction may improve transaction security. However, a network may have a large number of transactions, and selecting aCAfor each transaction usingPoSorPoAmay cause a significant amount of block propagation delay. Moreover, an increase in the number of participant nodes may increase the block propagation delay even further. Therefore, higher block propagation delay reduces network efficiency drastically. This paper proposes a different approach to increase the efficiency of Blockchain-based Public Key Infrastructure (BC – PKI). The proposed approach creates clusters of participant nodes based on their validation time, response time, and trust. This method selects a cluster based on the budget of response time and validation time given by the node that intends to start a transaction. Thereafter, the node which has the highest trust in that cluster is chosen as aCAfor the next transaction. Instead of searching on all participant nodes, our approach searches on the nodes of the chosen cluster which reduces the searching space of theCAselection process. This research work adopts a trust evaluation approach where the trust factor is quantified based on its experience and reputation. The node trust is reevaluated after every successful and unsuccessful transaction. A node that performs more successful transactions has more trust value. The node that has a higher trust value has a higher probability to be selected as aCAfor a transaction. The trust reevaluation process is followed by the clustering process. The result shows the proposed approach can reduce ~38.5% response time and ~2.2% validation time as compared to infrastructure which does not implement clustering. Additionally, the proposedCTB – PKIcan be used in Blockchain 2.0 and Blockchain 3.0-related applications.
The blockchain identity ecosystem offers the possibility of rejecting the outdated identity system and eliminate the intermediaries. Identity management, through blockchain, can allow individuals to take ownership of their identity by creating a global identity (ID) to serve multiple purposes. For user security and ledger consistency, asymmetric cryptography and distributed consensus algorithms can be implemented. Blockchain technology would be able to save costs and increase efficiency due to its key features such as decentralization, persistence, anonymity and auditability. In addition, the digital identity platform would save citizens' time in accessing or exchanging their personal data and records. Instead of being required to appear physically before the service provider, the user may be provided with a digital ID through his/her personal device, such as a smartphone, through which he/she can share his identity details with the service provider, using distributed ledger technology (DLT).
Most of the blockchain-based identity authentication systems are based on public blockchain, which are still essentially traditional centralized identity management and verification methods, making it difficult to meet the needs of trusted access and fine-grained access control in microgrids. Therefore, based on the FISCO BCOS consortium blockchain technology, a distributed identity authentication system supporting multi-center was designed. A DID-based identity management protocol to achieve autonomous control of user identity in a practical scenarios was designed. Distributed trusted access technology for end nodes in microgrids was studied, and privacy-protecting credentials based on zero-knowledge proof were designed. This scheme meets the requirements of trustworthy and verifiable user identity in different privacy security scenarios, and achieves autonomous control of entity identity, fine-grained access control and trusted data exchange. The usability and effectiveness of the proposed algorithm are demonstrated through system experiments and performance analysis.
Recently, two attacks were presented against Proof-of-Stake (PoS) Ethereum: one where short-range reorganizations of the underlying consensus chain are used to increase individual validators' profits and delay consensus decisions, and one where adversarial network delay is leveraged to stall consensus decisions indefinitely. We provide refined variants of these attacks, considerably relaxing the requirements on adversarial stake and network timing, and thus rendering the attacks more severe. Combining techniques from both refined attacks, we obtain a third attack which allows an adversary with vanishingly small fraction of stake and no control over network message propagation (assuming instead probabilistic message propagation) to cause even long-range consensus chain reorganizations. Honest-but-rational or ideologically motivated validators could use this attack to increase their profits or stall the protocol, threatening incentive alignment and security of PoS Ethereum. The attack can also lead to destabilization of consensus from congestion in vote processing.
Summary Today, the integrity and authenticity of digital documents and data are often hard to verify. Existing public key infrastructures (PKIs) are capable of certifying digital identities but do not provide solutions to store signatures immutably, and the process of certification is often not transparent. We propose Veritaa, a distributed public key infrastructure with an integrated signature store (DPKISS). The central part of Veritaa is the Graph of Trust that manages identity claims and singed declarations between identity claims and document identifiers. An application‐specific distributed ledger is used to store the transactions that form the Graph of Trust immutably. For the distributed certification of identity claims, a reputation system based on signed trust declarations and domain vetting is used. In this work, we have designed and implemented the proposed architecture of Veritaa, created a testbed, and performed several experiments. The experiments show the benefits and the high performance of Veritaa.
Lukas Alber, Stefan More, Sebastian Mödersheim, Anders Schlichtkrull
Trust policies enable the automated processing of trust decisions for electronic transactions. We consider the Trust Policy Language TPL of the LIGHTest project [Mö19] that was designed for businesses and organizations to formulate their trust policies. Using TPL, organizations can decide if and how they want to rely on existing trust schemes like Europe’s eIDAS or trust scheme translations endorsed by them. While the LIGHTest project is geared towards classical approaches like PKI-based trust infrastructures and X.509 certificates, novel concepts are on the rise: one example is the self-sovereign identity (SSI) model that enables users better control of their credentials, offers more privacy, and supports decentralized solutions. Since SSI is based on distributed ledger (DL) technology, it is a question of how TPL can be adapted so that organizations can continue to enjoy the benefits of flexible policy descriptions with automated evaluation at a very high level of reliability. Our contribution is a first step towards integrating SSI and the interaction with a DL into a Trust Policy Language. We discuss this on a more conceptual level and also show required TPL modifications. We demonstrate that we can integrate SSI concepts into TPL without changing the syntax and semantics of TPL itself and have to add new formats and introduce a new built-in predicate for interacting with the DL. Another advantage of this is that the “business logic” aspect of a policy does not need to change, enable re-use of existing policies with the new trust model.
Blockchains combine other technologies, such as cryptography, networking, and incentive mechanisms, to enable the creation, validation, and recording of transactions between participating nodes. A consensus algorithm is used in a blockchain system to determine the shared state among distributed nodes. An important component underlying any blockchain-based system is its consensus mechanism, which principally determines the performance and security of the overall system. As the nature of peer-to- peer(P2P) networks is open and dynamic, the security risk within that environment is greatly increased mostly because nodes can join and leave the network at will. Thus, it is important to have a system that can check against malicious behaviour. In this work, we propose a reputation-based consensus mechanism for blockchain-based systems, Proof-of-Reputation(PoR) where the nodes with the highest reputation values eventually become part of a consensus group that determines the state of the blockchain.
BACKGROUND: Health care systems are currently undergoing a digital transformation that has been primarily triggered by emerging technologies, such as artificial intelligence, the Internet of Things, 5G, blockchain, and the digital representation of patients using (mobile) sensor devices. One of the results of this transformation is the gradual virtualization of care. Irrespective of the care environment, trust between caregivers and patients is essential for achieving favorable health outcomes. Given the many breaches of information security and patient safety, today's health information system portfolios do not suffice as infrastructure for establishing and maintaining trust in virtual care environments. OBJECTIVE: This study aims to establish a theoretical foundation for a complex health care system intervention that aims to exploit a cryptographically secured infrastructure for establishing and maintaining trust in virtualized care environments and, based on this theoretical foundation, present a proof of concept that fulfills the necessary requirements. METHODS: This work applies the following framework for the design and evaluation of complex intervention research within health care: a review of the literature and expert consultation for technology forecasting. A proof of concept was developed by following the principles of design science and requirements engineering. RESULTS: This study determined and defined the crucial functional and nonfunctional requirements and principles for enhancing trust between caregivers and patients within a virtualized health care environment. The cornerstone of our architecture is an approach that uses blockchain technology. The proposed decentralized system offers an innovative governance structure for a novel trust model. The presented theoretical design principles are supported by a concrete implementation of an Ethereum-based platform called VerifyMed. CONCLUSIONS: A service for enhancing trust in a virtualized health care environment that is built on a public blockchain has a high fit for purpose in Healthcare 4.0.
Zero-knowledge proofs allow a prover to convince a verifier of the veracity of a statement without revealing any other information. An interesting class of zero-knowledge protocols are those following the MPC-in-the-head paradigm (Ishai et al., STOC '07) which use secure multiparty computation (MPC) protocols as the basis. Efficient instances of this paradigm have emerged as an active research topic in the last years, starting with ZKBoo (Giacomelli et al., USENIX '16). Zero-knowledge protocols are a vital building block in the design of privacy-preserving technologies as well as cryptographic primitives like digital signature schemes that provide post-quantum security. This work investigates the security of zero-knowledge protocols following the MPC-in-the-head paradigm. We provide the first machine-checked security proof of such a protocol on the example of ZKBoo. Our proofs are checked in the EasyCrypt proof assistant. To enable a modular security proof, we develop a new security notion for the MPC protocols used in MPC-in-the-head zero-knowledge protocols. This allows us to recast existing security proofs in a black-box fashion which we believe to be of independent interest.
Vinícius Lima, Filipe Andrade Bernardi, Rui Rijo, Jó Ueyama · 5 authors
BACKGROUND: Intensified research and innovation and rapid uptake of new tools, interventions, and strategies are crucial to fight Tuberculosis, the world's deadliest infectious disease. The sharing of health data remains a significant challenge. Data consumers must be able to verify the consistency and integrity of data. Solutions based on distributed ledger technologies may be adequate, where each member in a network holds a unique credential and stores an identical copy of the ledger and contributes to the collective process of validating and certifying digital transactions. OBJECTIVES: This work proposes a mechanism and presents a use case in Digital Health to allow the verification of integrity and immutability of TB electronic health records. METHODS: IOTA was selected as a supporting tool due to its data immutability, traceability and tamper-proof characteristics. RESULTS: A mechanism to verify the integrity of data through hash functions and the IOTA network is proposed. Then, a set of TB related information systems was integrated with the network. CONCLUSION: IOTA technology offers performance and flexibility to enable a reliable environment for electronic health records.
In recent years, we have witnessed the evolutionary development of a new breed of distributed systems. Systems of this type share a number of characteristics – highly decentralized, of Internet-grade scalability, and autonomous within their administrative domains. Most importantly, they are expected to operate collaboratively across both known and unknown domains. Prime examples include peer-to-peer applications and open web services. Typically, authorization in distributed systems is identity-based, e.g. access control lists. However, approaches based on predefined identities are unsuitable for the new breed of distributed systems because of the need to deal with unknown users, i.e. strangers, and the need to manage a potentially large number of users and/or resources. Furthermore, effective administration and management of authorization in such systems requires: (1) natural mapping of organizational policies into security policies; (2) managing collaboration of independently administered domains/organizations; (3) decentralization of security policies and policy enforcement. This thesis describes Fidelis, a trust management framework designed to address the authorization needs for the next-generation distributed systems. A trust management system is a term coined to refer to a unified framework for the specification of security policies, the representation of credentials, and the evaluation and enforcement of policy compliances. Based on the concept of trust conveyance and a generic abstraction for trusted information as trust statements, Fidelis provides a generic platform for building secure, trust-aware distributed applications. At the heart of the Fidelis framework is a language for the specification of security policies, the Fidelis Policy Language (FPL), and the inference model for evaluating policies expressed in FPL. With the policy language and its inference model, Fidelis is able to model recommendation-style policies and policies with arbitrarily complex chains of trust propagation. Web services have rapidly been gaining significance both in industry and research as a ubiquitous, next-generation middleware platform. The second half of the thesis describes the design and implementation of the Fidelis framework for the standard web service platform. The goal of this work is twofold: first, to demonstrate the practical feasibility of Fidelis, and second, to investigate the use of a policy-driven trust management framework for Internet-scale open systems. An important requirement in such systems is trust negotiation that allows unfamiliar principals to establish mutual trust and interact with confidence. Addressing this requirement, a trust negotiation framework built on top of Fidelis is developed. This thesis examines the application of Fidelis in three distinctive domains: implementing generic role-based access control, trust management in the World Wide Web, and an electronic marketplace comprising unfamiliar and untrusted but collaborative organizations.
Access control management in a collaborative environment composed of a multitude of distributed autonomous organizations is a challenging task. To answer the challenge, in this paper we propose a novel approach that incorporates semantic technologies in the Attribute-Based Access Control (ABAC) approach. Building on the basic principles of ABAC, our approach allows for a highly expressive modeling of the context in which access decisions are made, by providing mechanisms to describe rich relationships among entities, which can evolve over time. In addition, our system works in a truly decentralized manner, which makes it suitable for geographically distributed enterprise systems. We show the feasibility in practice of our approach through some experimental results.
Jan 1, 2021·Proceedings of the 36th IFIP TC 11 International Conference on ICT Systems Security and Privacy Protection (IFIP SEC 2021)/IFIP Advances in Information and Communication Technology, vol. 625, 2021, 19-35
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.
The quick jumps in developing new digital identity technologies have resulted in this trend of developing privacy-preserving solutions in Know Your Customer (KYC) verification systems. This article delves into the evolution of an Advanced Digital Identity Orchestration Engine to enhance privacy protection in the KYC processes. With the rise of concerns surrounding data privacy and security, traditional knowledge of customer systems which are based on centralized database, have faced major challenges including data breaches and unauthorized access. In contrast, the proposed identity orchestration engine draws on the use of Self-Sovereign Identity (SSI) principles, blockchain technology, and verifiable credentials to offer a decentralized, secure and privacy-preserving solution to identity management problem. This engine allows users to manage their personal identity information, and selectively share their information with entities they trust without losing their privacy. By leveraging decentralized identifiers (DIDs) and public key cryptography, the system is enabled to ensure the sensitive data isn't kept in a central place causing reduction in the odds of unauthorized access. Furthermore, features such as zero knowledge proofs (ZKPs) and selective disclosure provide the option for a granular control on what data is shared to ensure that only the required information is provided to comply with regulation requirements. This article also talks about integrating the orchestration engine with existing frameworks for KYC and explores the scalability, interoperability, and potential for this engine to help increase inclusivity in digital identity management. Through case studies and real-world examples, the paper points out the efficiency in working of this engine in getting better security and privacy and user experience in the process of KYC verification. Ultimately, the solution proposed creates a major step forward to privacy-preserving and user-centric digital Identity systems adapted both globally to regulatory requirements and to increase trust in digital financial services.
Proof of stake (PoS), aiming at replacing Proof of work (PoW) in blockchain consensus, has drawn great attention from academia and industry. We present “Baguena”, a novel PoS protocol for public blockchain with high practicality and security. It uses a special designed algorithm with properties of uniqueness and anonymity for leader selection, and uses the longest chain rule for chain selection. Besides, entropy is introduced to prevent manipulation of leader selection process by simulating a random beacon based on Publicly verifiable secret sharing (PVSS) and threshold signature with only a linear number of exponentiations. We analyze the protocol's security by a threat model and design a robust delegation mechanism based on triple Elliptic curve digital signature algorithm (ECDSA) proxy signature. We implement Baguena and evaluate its performance on 100 Amazon EC2 virtual machines simulating 50k users, which shows that Baguena confirms transactions in 2 minutes, achieves 2.16x of Algorand's throughput and 6.95x of Ouroboros' throughput.
Asset custody is a core financial service in which the custodian holds in-safekeeping assets on behalf of the client. Although traditional custody service is typically endorsed by centralized authorities, decentralized custody scheme has become technically feasible since the emergence of digital assets, and furthermore, it is greatly needed by new applications such as blockchain and DeFi (Decentralized Finance). In this work, we propose a framework of decentralized asset custody scheme that is able to support a large number of custodians and safely hold customer assets of multiple times the value of the total security deposit. The proposed custody scheme distributes custodians and assets into many custodian groups via combinatorial designs, where each group fully controls the assigned assets. Since every custodian group is small, the overhead cost is significantly reduced. The liveness is also improved because even a single alive group would be able to process transactions. The security of this custody scheme is guaranteed under the rational adversary model, such that any adversary corrupting a bounded fraction of custodians cannot move assets more than the security deposit paid. We further analyze the security and performance of our constructions from both theoretical and experimental sides and give explicit examples with concrete numbers and figures for a better understanding of our results.
Context: Smart contracts and DApps are becoming increasingly important and widespread. DApps are often business-critical, and strong security guarantees must be ensured. However, developing safe and reliable smart contracts remains a challenging task. Despite growing literature, simple and actionable tools to address security issues are still lacking. Objective: This study identifies design patterns and best practices for DApp security. We categorize them into twelve critical areas based on their security goals and map them to the architecture of decentralized applications. For each item, we define concrete actions to support secure implementation. These are further structured into three security assurance checklists. Method: We analyze existing literature and manually review 224 security items, consolidating duplicates and harmonizing terminology. This process results in 84 unique items, divided into 36 design patterns and 48 best practices, further grouped into 12 categories. We also map the items into three checklists based on the development phase of DApp lifecycle. Finally, for each pattern and practice, we derive 374 actionable security tasks to guide secure development. Results: To the best of our knowledge, this is the most comprehensive and structured collection of DApp security items to date. The proposed framework and checklists help developers ensure the consistent and complete application of secure design principles. Conclusion: Focusing on Ethereum and Solidity, we present a comprehensive framework for improving DApp security. Our work supports ongoing efforts to reduce vulnerabilities in decentralized applications and provides developers with practical tools to build safer, more reliable systems.
Given that Proof-of-Work (PoW) and Proof-of-Stake (PoS) are plutocratic, and other common consensus protocols are mostly permission-based, we look for a consensus protocol that will suit the needs of e-Democracy. In particular, what we need is a distributed ledger that will record and, to the possible extent, execute the public will. We propose a combination of any given permission-based protocol together with a trust graph between the nodes, which supplies the required permission for new nodes. As a result, the consensus protocol reaches consensus at every iteration between a known list of agents and then updates this list between iterations. This paper is based on prior work that shows the conditions under which a community can grow while maintaining a bounded number of byzantines. It combines a permission-based consensus protocol (such as pBFT) with a community expansion algorithm (such as the one in the prior work) to arrive at a consensus protocol in which the set of agents can change in time, while being sybil-resilient.
Vulnerabilities of smart contract are certainly one of the limiting factors for wider adoption of blockchain technology. Smart contracts written in Solidity language are considered due to common adoption of the Ethereum blockchain platform. Despite its popularity, the semantics of the language is not completely documented and relies on implicit mechanisms not publicly available and as such vulnerable to possible attacks. In addition, creating formal semantics for the higher-level language provides support to verification mechanisms. In this paper, a novel approach to smart contact verification is presented that uses ontologies in order to leverage semantic annotations of the smart contract source code combined with semantic representation of domain-specific aspects. The following aspects of smart contracts, apart from source code are taken into consideration for verification: business logic, domain knowledge, run-time state changes and expert knowledge about vulnerabilities. Main advantages of the proposed verification approach are platform independence and extendability.
This paper presents an architecture, based on Distributed Ledger Technologies\n(DLTs) and Decentralized File Storage (DFS) systems, to support the use of\nPersonal Information Management Systems (PIMS). DLT and DFS are used to manage\ndata sensed by mobile users equipped with devices with sensing capability. DLTs\nguarantee the immutability, traceability and verifiability of references to\npersonal data, that are stored in DFS. In fact, the inclusion of data digests\nin the DLT makes it possible to obtain an unalterable reference and a\ntamper-proof log, while remaining compliant with the regulations on personal\ndata, i.e. GDPR. We provide an experimental evaluation on the feasibility of\nthe use of DFS. Three different scenarios have been studied: i) a proprietary\nIPFS approach with a dedicated node interfacing with the data producers, ii) a\npublic IPFS service and iii) Sia Skynet. Results show that through proper\nconfiguration of the system infrastructure, it is viable to build a\ndecentralized Personal Data Storage (PDS).\n
Yanhong Xu, Reihaneh Safavi–Naini, Khoa Nguyen, Huaxiong Wang
Policy-based signatures (PBS) were proposed by Bellare and Fuchsbauer (PKC 2014) to allow an {\em authorized} member of an organization to sign a message on behalf of the organization. The user's authorization is determined by a policy managed by the organization's trusted authority, while the signature preserves the privacy of the organization's policy. Signing keys in PBS do not include user identity information and thus can be passed to others, violating the intention of employing PBS to restrict users' signing capability. In this paper, we introduce the notion of {\em traceability} for PBS by including user identity in the signing key such that the trusted authority will be able to open a suspicious signature and recover the signer's identity should the needs arise. We provide rigorous definitions and stringent security notions of traceable PBS (TPBS), capturing the properties of PBS suggested by Bellare-Fuchsbauer and resembling the "full traceability" requirement for group signatures put forward by Bellare-Micciancio-Warinschi (Eurocrypt 2003). As a proof of concept, we provide a modular construction of TPBS, based on a signature scheme, an encryption scheme and a zero-knowledge proof system. Furthermore, to demonstrate the feasibility of achieving TPBS from concrete, quantum-resistant assumptions, we give an instantiation based on lattices.
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