Chris Pollett, Thomas H. Austin, Katerina Potika, Justin Rietz
Proof-of-stake cryptocurrencies avoid many of the computational and environmental costs associated with proof-of-work protocols. However, they must address the nothing-at-stake problem, where a validator might attempt to sign off on competing blocks, with the hopes of earning coins regardless of which block becomes accepted as part of the blockchain. Cryptocurrencies such as Tendermint resolve this challenge by requiring validators to em bond coins, which can be seized from a validator that is caught signing two competing blocks. Nevertheless, as the number of validators increases, it becomes more and more infeasible to effectively monitor all validators. In this work, we incentivize proper block monitoring by allowing validators to form tontines. Tontines are financial agreements where payouts to each member increase as the number of members decreases. In our system, a tontine is a group of validators that monitor each other's behavior, "murdering" any cheating tontine members to seize their stake. As the number of validators in a tontine is smaller than the number of validators in the currency as a whole, members can effectively police each other. We propose two methods whereby a Tendermint-like currency can be extended to allow for the creation of tontines: a pure proof-of-stake model, and a hybrid proof-of-stake/proof-of-work model. We describe snitch mechanisms for both the inter-and intra-tontine setting, argue our incentive mechanisms increase monitoring, and describe how it handles a variety of possible attacks.
Distributed Ledgers and Blockchains involve decentralized networking technologies such as peer-to-peer networks. Both permissioned and unpermissioned blockchains are designed to tolerate and to overcome the failure of individual nodes, which need to update themselves once they reconnect to the blockchain network. At the same time, it is important to avoid accidental network partitioning, since partitioning can lead to inconsistent "multiple truths" and violate the shared consensus about the global state, which must be maintained across all active and re-emerging nodes. In general, reconciling inconsistent "multiple truths" would require the deletion of information which was persisted to the blockchain (in one of the network partitions), and such removal violates the core blockchain principle of audit-proof and tamper-proof "write once read many" access (WORM). However, current mainstream implementations such as Ethereum do not protect against network partitioning (either by accident or caused by an attack), and there is no research on how the consensus implementations behave in the presence of network partitioning. Given the differences in design and implementation across ledgers and blockchains, a systematic analytic approach must be established before partitioning prevention in specific products is studied. The contribution of this paper is a foundational analysis of enterprise-grade consensus protocols, including design recommendations for partitioning avoidance for Proof-of-Authority in Hyperledger Fabric. We also survey related work and lay out next research steps.
In the first part of this work, we present, model and analyze a randomized automated peering model, that can be implemented to any distributed system. We conclude that the scheme has some desirable properties (specifically, a reasonable message overhead, a reasonable distribution of the numbers of peers of a node, and a negligible probability of an attack by a malicious actor to be successful). In the second part, we present an article published in the volume 136 of the journal Computers & Industrial Engineering, in October of 2019 (DOI 10.1016=j.cie.2019.07.025). In the paper, we analyze the Nash Equilibria of a graph attachment game, defined to represent the different strategies that malicious actors can use to take certain advantages in a DAG-based (i.e., based on Directed Acyclic Graphs) distributed ledger system. We prove the existence of almost symmetric Nash equilibria for the system where a part of players tries to optimize their attachment strategies and another part follows a default one. We also present simulations that show that the selfish players will not choose strategies that are considerably different that the recommended one.
A consensus algorithm lies at the core of every distributed ledger as it defines how the constituent parts of the distributed system ensure that they share identical ledger copies. For a broad range of promising applications of distributed ledger technology, the parties responsible for the application can specify and control the distributed entities maintaining the ledger. Since the faulty behavior of any such entity must not cause inconsistencies in the ledger and access to the ledger is restricted, Byzantine agreement is a viable candidate as a backbone for such so-called permissioned distributed ledgers. In this setting, a primary objective is to maximize throughput, i.e., the rate at which transactions can be processed, which requires a quick settlement at the consensus layer.
This paper intends to propose the architecture of a blockchain-agnostic\nprotocol designed for communication of blockchains amongst each other (i.e.\ncross-chain), and for blockchains with the outside world (i.e. data oracles).\nThe expansive growth of cutting-edge technology in the blockchain industry\noutlines the need and opportunity for addressing oracle consensus in a manner\nboth technologically and economically efficient as well as futureproof.\nBlockchain-agnosticism is inherently limited if proposing a technological\nsolution involves adding one more architectural layer. As such, Gravity\nprotocol is designed to be a truly blockchain-agnostic protocol. By ensuring\nparity through direct integration and by leveraging the stability and security\nof the respective interconnected ecosystems, Gravity circumvents the need for a\ndedicated, public blockchain and a native token. Ultimately, Gravity protocol\nintends to address scalability challenges by providing a solid infrastructure\nfor the creation of gateways, cross-chain applications, and sidechains. This\npaper introduces and defines the concept of Oracle Consensus and its\nimplementation in the Gravity protocol named the Pulse Consensus algorithm. The\nproposed consensus architecture allows Gravity to be considered a singular\ndecentralized blockchain-agnostic oracle.\n
Gamze Gürsoy, Robert Bjornson, Molly E. Green, Mark Gerstein
BACKGROUND: Genomic variants are considered sensitive information, revealing potentially private facts about individuals. Therefore, it is important to control access to such data. A key aspect of controlled access is secure storage and efficient query of access logs, for potential misuse. However, there are challenges to securing logs, such as designing against the consequences of "single points of failure". A potential approach to circumvent these challenges is blockchain technology, which is currently popular in cryptocurrency due to its properties of security, immutability, and decentralization. One of the tasks of the iDASH (Integrating Data for Analysis, Anonymization, and Sharing) Secure Genome Analysis Competition in 2018 was to develop time- and space-efficient blockchain-based ledgering solutions to log and query user activity accessing genomic datasets across multiple sites, using MultiChain. METHODS: MultiChain is a specific blockchain platform that offers "data streams" embedded in the chain for rapid and secure data storage. We devised a storage protocol taking advantage of the keys in the MultiChain data streams and created a data frame from the chain allowing efficient query. Our solution to the iDASH competition was selected as the winner at a workshop held in San Diego, CA in October 2018. Although our solution worked well in the challenge, it has the drawback that it requires downloading all the data from the chain and keeping it locally in memory for fast query. To address this, we provide an alternate "bigmem" solution that uses indices rather than local storage for rapid queries. RESULTS: We profiled the performance of both of our solutions using logs with 100,000 to 600,000 entries, both for querying the chain and inserting data into it. The challenge solution requires 12 seconds time and 120 Mb of memory for querying from 100,000 entries. The memory requirement increases linearly and reaches 470 MB for a chain with 600,000 entries. Although our alternate bigmem solution is slower and requires more memory (408 seconds and 250 MB, respectively, for 100,000 entries), the memory requirement increases at a slower rate and reaches only 360 MB for 600,000 entries. CONCLUSION: Overall, we demonstrate that genomic access log files can be stored and queried efficiently with blockchain. Beyond this, our protocol potentially could be applied to other types of health data such as electronic health records.
Stefano Angieri, Marcelo Bagnulo, Alberto García-Martínez, Bingyang Liu · 5 authors
In this paper, we present InBlock4, a blockchain-based alternative to RPKI for the provision of Route Origin validation for BGP. InBlock4 embeds an alternative trust model to protect entities obtaining a resource allocations from errors and abuses from other entities in the allocation hierarchy. InBlock4 is compatible with BGPsec. Moreover, InBlock4 can be bootstrapped using the information in the RPKI and it can coexists with RPKI-based route origin validation. In the paper, we also present a working implementation of InBlock4 for Ethereum and we quantify its performance.
As the infrastructure to provide support for distributed database management systems, the distributed database platform is very important to unify the management of data distributed in intricate environments. However, a traditional distributed database platform with centralized entities faces diverse and serious threats when the central entity is compromised. Consensus mechanisms in distributed ledger technology (DLT) can enhance the capability of defending threats by decentralizing the platform, but the efficiency and cost of consensus mechanisms in classic blockchain techniques are notable issues. In this paper, we propose a novel decentralized database platform, named Dagbase, with the support of an efficient and cost-effective consensus mechanism that uses the directed acyclic graph (DAG) as the structure. Dagbase decentralizes the management and distributes data to prevent threats in untrustworthy environments, which gains benefits from recent DLT. The performance of near-native data reading and high-efficiency data writing is ensured by a layered architecture and DAG-based consensus. Furthermore, we ensure flexibility by decoupling the consensus mechanism from the architecture. Dagbase is also easy-to-use and can be integrated with mainstream database products seamlessly on account of great interoperability. The implementation demonstrates our work and the security and performance analysis are enforced for evaluation.
Since Bitcoin's seminal work of achieving consensus under the assumption that more than 51% computational power is honest, many researchers have proposed various kinds of consensus protocols. In recent years, there has been a trend in designing proof of stake (PoS) based consensus protocols. Unfortunately, PoS based consensus protocols are inherently not secure and are vulnerable to “long range attacks”. Thus PoS based blockchains have the potential risk of being forked with a minimal cost for double spending. In this paper, we propose a PoS protocol that is secure against long range attack based double spending. The security is achieved using secure randomness beacons generated by tamper proof hardware modules.
The scope of the existing distributed ledger technologies is divergent in terms of technological features, as well as in their acceptance among the user and developer communities. In this paper, we propose a set of diverse criteria for the evaluation of a distributed ledger ecosystem, which does not focus only on the technological aspects of viable solutions. They also consider decentralized application development perspective and sustainability of its use. We provide a brief overview of some of the alternative distributed ledger ecosystems for the development and deployment of business and IoT decentralized applications. The set of investigated technologies and networks includes Ethereum, Hyperledger, Hedera Hashgraph, EOS, Corda, IOTA, and Multichain.
The celebrated result of Fischer, Lynch and Paterson is the fundamental lower\nbound for asynchronous fault tolerant computation: any 1-crash resilient\nasynchronous agreement protocol must have some (possibly measure zero)\nprobability of not terminating. In 1994, Ben-Or, Kelmer and Rabin published a\nproof-sketch of a lesser known lower bound for asynchronous fault tolerant\ncomputation with optimal resilience against a Byzantine adversary: if $n\\le 4t$\nthen any t-resilient asynchronous verifiable secret sharing protocol must have\nsome non-zero probability of not terminating.\n Our main contribution is to revisit this lower bound and provide a rigorous\nand more general proof. Our second contribution is to show how to avoid this\nlower bound. We provide a protocol with optimal resilience that is almost\nsurely terminating for a strong common coin functionality. Using this new\nprimitive we provide an almost surely terminating protocol with optimal\nresilience for asynchronous Byzantine agreement that has a new fair validity\nproperty. To the best of our knowledge this is the first asynchronous Byzantine\nagreement with fair validity in the information theoretic setting.\n
The interblockchain communication protocol (IBC) is an end-to-end, connection-oriented, stateful protocol for reliable, ordered, and authenticated communication between modules on separate distributed ledgers. IBC is designed for interoperation between heterogenous ledgers arranged in an unknown, dynamic topology, operating with varied consensus algorithms and state machines. The protocol realises this by specifying the sufficient set of data structures, abstractions, and semantics of a communication protocol which once implemented by participating ledgers will allow them to safely communicate. IBC is payload-agnostic and provides a cross-ledger asynchronous communication primitive which can be used as a constituent building block by a wide variety of applications.
Duncan Thomson, Steven Bodie, David E. Bryson, Timothy S. Luc · 5 authors
This paper describes a concept and a prototype for sharing flight information using blockchain technology. Providing all stakeholders access to complete, consistent, and up-to-date information about each flight facilitates efficient aviation operations. Existing flight information exchange methods are limited; the concept of a “flight object” that provides a complete solution for all stakeholders has yet to be realized. A complete solution requires either a centrally administered data store, which is unsuitable for an international context, or a distributed ledger. Distributed ledgers are at the heart of blockchain technology, which makes this technology a good match for implementing the flight object. The authors have proven it is possible to provide a complete flight object solution using blockchain technology by demonstrating a prototype based on Tendermint: an open-source blockchain implementation. The demonstrated solution offers additional benefits like strong integrity guarantees and role-based update permissions enforcement. Prototype performance indicates a production implementation is likely to provide sufficient speed and capacity to support global aviation operations for flight planning negotiation, as well as possible future concepts such as trajectory-based operations and international flow management. The paper’s conclusion discusses steps necessary for the flight object sharing capability to be adopted as the basis for a real-world international aviation solution.
Tactical Data Link (TDL) is a communication system that utilizes a particular message format and a protocol to transmit data via wireless channels in an instant, automatic, and secure way. So far, TDL has shown its excellence in military applications. Current TDL adopts a distributed architecture to enhance anti-destruction capacity. However, It still faces a problem of data inconsistency and thus cannot well support cooperation across multiple militarily domains. To tackle this problem, we propose to leverage blockchain to build an automatic and adaptive data transmission control scheme for TDL. It achieves automatic data transmission and realizes information consistency among different TDL entities. Besides, applying smart contracts based on blockchain further enables adjusting data transmission policies automatically. Security analysis and experimental results based on simulations illustrate the effectiveness and efficiency of our proposed scheme.
Many researchers challenge the possibility of using blockchain and smart contracts to disrupt the Internet of Things (IoT) architecture because of their security and decentralization guarantees. However, the state-of-the-art blockchain architecture is not scalable enough to satisfy the requirements of massive data traffics in the IoT environment. The main reason for this issue is one needs to choose the consensus trade-off between either coping with a high throughput or a high number of nodes. Consequently, this issue prevents the applicability of blockchain for IoT use cases. In this paper, we propose a scalable two-tiered hierarchical blockchain architecture for IoT. The first tier is a Core Engine, which is based on a Practical Byzantine Fault Tolerance (PBFT) consensus to cope with a high throughput, that supervises the underlying subordinate engines (sub-engines) as its second tier. This second tier comprises of the Payment, Compute, and Storage Engine, respectively. We can deploy multiple instances of these sub-engines as many as we need and as local as possible near to the IoT domains, where IoT devices reside, to cope with a high number of nodes. Furthermore, to further extend the scalability of the proposed architecture, we also provide additional scalability features on the Core Engine such as request aggregation, request prioritization, as well as sub-engine parallelism. We implement all of our engines and expose them to IoT applications through the Engine APIs. With these APIs, developers can build and run IoT applications in our architecture. Our evaluation results show that our proposed features on the Core Engine can indeed enhance the overall performance of our architecture. Moreover, based on our proof-of-concept IoT car rental application, we also show that the interoperability between sub-engines through the Core Engine is possible, even when the particular sub-engine is under sub-engine parallelism.
Blockchain protocols differ in fundamental ways, including the mechanics of selecting users to produce blocks (e.g., proof-of-work vs. proof-of-stake) and the method to establish consensus (e.g., longest chain rules vs. BFT-inspired protocols). These fundamental differences have hindered "apples-to-apples" comparisons between different categories of blockchain protocols and, in turn, the development of theory to formally discuss their relative merits. This paper presents a parsimonious abstraction sufficient for capturing and comparing properties of many well-known permissionless blockchain protocols, simultaneously capturing essential properties of both proof-of-work and proof-of-stake protocols, and of both longest-chain-type and BFT-type protocols. Our framework blackboxes the precise mechanics of the user selection process, allowing us to isolate the properties of the selection process which are significant for protocol design. We illustrate our framework's utility with two results. First, we prove an analog of the CAP theorem from distributed computing for our framework in a partially synchronous setting. This theorem shows that a fundamental dichotomy holds between protocols (such as Bitcoin) that are adaptive, in the sense that they can function given unpredictable levels of participation, and protocols (such as Algorand) that have certain finality properties. Second, we formalize the idea that proof-of-work (PoW) protocols and non-PoW protocols can be distinguished by the forms of permission that users are given to carry out updates to the state.
Modern computing systems are highly concurrent. Threads run concurrently in shared-memory multi-core systems, and programs run in different servers communicating by sending messages to each other. Concurrent programming is hard because it requires to cope with many possible, unpredictable behaviors of the processes, and the communication media. The article argues that right from the start in 1960's, the main way of dealing with concurrency has been by reduction to sequential reasoning. It traces this history, and illustrates it through several examples, from early ideas based on mutual exclusion (which was initially introduced to access shared physical resources), passing through consensus and concurrent objects (which are immaterial data), until today distributed ledgers. A discussion is also presented, which addresses the limits that this approach encounters, related to fault-tolerance, performance, and inherently concurrent problems.
Blockchain Technology is exclusively used to make online transactions secure by maintaining a distributed and decentralized ledger of records across multiple computers. Tendermint is a general-purpose blockchain engine that is composed of two parts; Tendermint Core and the blockchain application interface. The application interface makes Tendermint suitable for a wide range of applications. In this paper, we analyze and improve Practical Byzantine Fault Tolerant (PBFT), a consensus-based Tendermint blockchain algorithm. In order to avoid negative issues of locks, we first propose a lock-free algorithm for blockchain in which the proposal and voting phases are concurrent whereas the commit phase is sequential. This consideration in the algorithm allows parallelism. Secondly, a new methodology is used to decide the size of the voter set which is a subset of blockchain nodes, further investigating the block sensitivity and trustworthiness of nodes. Thirdly, to fairly select the voter set nodes, we employ the random walk algorithm. Fourthly, we imply the wait-freedom property by using a timeout due to which all blocks are eventually committed or aborted. In addition, we have discussed voting conflicts and consensuses issues that are used as a correctness property, and provide some supportive techniques.
Marcela Tuler de Oliveira, Lúcio Henrik A. Reis, Dianne S. V. Medeiros, Ricardo C. Carrano · 6 authors
Consensus mechanisms in blockchain applications allow mistrusting peers to agree on the global state of the chain. Most of the existing consensus mechanisms, however, are constrained by low efficiency and high energy consumption. In this paper, we propose the Blockchain Reputation-Based Consensus (BRBC) mechanism in which a node must have the reputation score higher than a given network trust threshold before being allowed to insert a new block in the chain. A randomly-selected set of judges monitors the behaviour of each node involved in the consensus and updates the node reputation score. Every cooperative behaviour results in a reward, and a non-cooperative or malicious behaviour results in a punishment. BRBC also uses the reputation score to revoke access to nodes with a reputation score below a given threshold. We present a security analysis, and we demonstrate that BRBC resists against a set of known attacks in the blockchain network. Finally, we simulate a blockchain network to assert the mechanism scalability and resilience to malicious actions in various network scenarios and different rates of malicious actions. The results show BRBC to be efficient to expel all nodes that acted with more than 50% of malicious actions.
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