This paper introduces some trust issues for blockchain transactions. Such transactions rely on ECDSA signature based on 32 bytes secret keys. Because these keys can be stolen or hacked, we suggest to prevent these risks by using javacard secure elements. We detailed the interface of a Crypto Currency Smart Card (CCSC) designed over a JC3.04 standard platform. We details two use cases. First deals with deployment of the CCSC application in low cost low power object powered by an open hardware (arduino) platform, and integrates sensor data in ethereum transactions. Second proposes the deployment in the cloud of CCSC javacards plugged to RACS servers, in order to enable the remote and safe use of ECDSA signature.
As proof-of-work blockchains are inherently energy greedy and offer probabilistic guarantees, blockchains based on Byzantine consensus appear as a promising technology to track billions of connected devices. In this paper, we evaluate the performance of prominent blockchains that solve the classic Byzantine consensus problem. Our results show that while offering reasonable throughput their performance usually do not scale to tens of devices and drops dramatically as the number of devices increases. This study motivates the need for solutions that solves the Blockchain consensus problem, a scalable variant of the classic Byzantine consensus problem but dedicated to blockchains.
Enterprises have paid attention to blockchain (BC), recently permissioned BC characterized with smart-contract, where business transactions among inter-authorized companies (forming consortium) can automatically be executed based on distributed consensus protocol over user-defined business logics pre-built with program codes. A single BC system will be built across multiple management domains having different operational policies, e.g., datacenter of each organization; this will trigger a problem that its system operations (e.g., backup) will become time-consuming and costly due to the difficulty in unifying and/or adjusting operational policy, schedule, etc. Toward solving the problem, we propose an operations execution method for BC systems; a primary idea is to define operations as smart-contract so that unified and synchronized cross-organizational operations can be executed effectively by using BC-native features. We de-sign the proposed method as hybrid architecture including in-BC consensus establishment and out-BC event-based instruction execution, in order to be adaptable to the recent heterogeneous BC architecture. Performance evaluation using a prototype with Hyperledger Fabric v1.0 shows that the proposed method can start executing operations within 5 seconds. Furthermore, cost evaluation using model-based estimation shows that the total yearly cost of monthly operations on a 5-organizational BC system could be reduced by 61 percent compared to a conventional manual method.
The brave new world of blockchain potentially transforms the financial structures we have come to know and feel ambivalent about. What does a decentralized, secure system mean for our society?
A. Nunez Mencias, Donna N. Dillenberger, P. Novotny, Fanni Tóth · 11 authors
Blockchain is a technology that has been available for several years and has already had several generations. Multiple implementations exist. In this paper, we describe how one of them, the Hyperledger Fabric, is used today to demonstrate the wide usage of the technology for multiple markets beyond finance and cryptocurrency. The use cases highlight the relevance of security—due to the type of data and the distributed foundation of blockchain—and of system performance to enable the use cases in production. Security and performance are the base for the architecture of blockchain on the IBM LinuxONE systems. The Secure Service Container prevents tampering, and the cryptocard usage hardens the solution—and the performance optimization in the compiler, cryptoinstructions, and large caches provides the performance. These optimizations have been further extended with the IBM z14 beyond previous IBM Z generations. In this paper, we describe how a cluster topology is used to implement a high-availability service that scales dynamically from small networks to large ones using the hot plug capabilities of the IBM LinuxONE systems.
Elli Androulaki, Artem Barger, Vita Bortnikov, Christian Cachin · 21 authors
Fabric is a modular and extensible open-source system for deploying and operating permissioned blockchains and one of the Hyperledger projects hosted by the Linux Foundation (www.hyperledger.org). Fabric is the first truly extensible blockchain system for running distributed applications. It supports modular consensus protocols, which allows the system to be tailored to particular use cases and trust models. Fabric is also the first blockchain system that runs distributed applications written in standard, general-purpose programming languages, without systemic dependency on a native cryptocurrency. This stands in sharp contrast to existing blockchain platforms that require "smart-contracts" to be written in domain-specific languages or rely on a cryptocurrency. Fabric realizes the permissioned model using a portable notion of membership, which may be integrated with industry-standard identity management. To support such flexibility, Fabric introduces an entirely novel blockchain design and revamps the way blockchains cope with non-determinism, resource exhaustion, and performance attacks. This paper describes Fabric, its architecture, the rationale behind various design decisions, its most prominent implementation aspects, as well as its distributed application programming model. We further evaluate Fabric by implementing and benchmarking a Bitcoin-inspired digital currency. We show that Fabric achieves end-to-end throughput of more than 3500 transactions per second in certain popular deployment configurations, with sub-second latency, scaling well to over 100 peers.
An atomic cross-chain swap is a distributed coordination task where multiple parties exchange assets across multiple blockchains, for example, trading bitcoin for ether. An atomic swap protocol guarantees (1) if all parties conform to the protocol, then all swaps take place, (2) if some coalition deviates from the protocol, then no conforming party ends up worse off, and (3) no coalition has an incentive to deviate from the protocol. A cross-chain swap is modeled as a directed graph ${\cal D}$, whose vertexes are parties and whose arcs are proposed asset transfers. For any pair $({\cal D},L)$, where ${\cal D} = (V,A)$ is a strongly-connected directed graph and $L \subset V$ a feedback vertex set for ${\cal D}$, we give an atomic cross-chain swap protocol for ${\cal D}$, using a form of hashed timelock contracts, where the vertexes in $L$ generate the hashlocked secrets. We show that no such protocol is possible if ${\cal D}$ is not strongly connected, or if ${\cal D}$ is strongly connected but $L$ is not a feedback vertex set. The protocol has time complexity $O(diam({\cal D}))$ and space complexity (bits stored on all blockchains) $O(|A|^2)$.
As a decentralized and distributed secure storage technology, the notion of blockchain is now widely used for electronic trading in finance, for issuing digital certificates, for copyrights management, and for many other security-critical applications. With applications in so many domains with high-assurance requirements, the formalization and verification of safety and security properties of blockchain becomes essential, and the aim of the present paper. We present the model-based formalization, simulation and verification of a blockchain protocol by using the SDL formalism of Telelogic Tau. We consider the hierarchical and modular SDL model of the blockchain protocol and exercise a methodology to formally simulate and verify it. This way, we show how to effectively increase the security and safety of blockchain in order to meet high assurance requirements demanded by its application domains. Our work also provides effective support for assessing different network consensus algorithms, which are key components in blockchain protocols, as well as on the topology of blockchain networks. In conclusion, our approach contributes to setting up a verification methodology for future blockchain standards in digital trading.
Bitcoin, as well as many of its successors, require the whole transaction record to be reliably acquired by all nodes to prevent double-spending. Recently, many blockchains have been proposed to achieve scale-out throughput by letting nodes only acquire a fraction of the whole transaction set. However, these schemes, e.g., sharding and off-chain techniques, suffer from a degradation in decentralization or the capacity of fault tolerance. In this paper, we show that the complete set of transactions is not a necessity for the prevention of double-spending if the properties of value transfers is fully explored. In other words, we show that a value-transfer ledger like Bitcoin has the potential to scale-out by its nature without sacrificing security or decentralization. Firstly, we give a formal definition for the value-transfer ledger and its distinct features from a generic database. Then, we introduce an off-chain based scheme with a shared main chain for consensus and an individual chain for each node for recording transactions. A locally executable validation scheme is proposed with uncompromising validity and consistency. A beneficial consequence of our design is that nodes will spontaneously try to reduce their transmission cost by only providing the transactions needed to show that their transactions are double-spending-proof. As a result, the network is sharded as each node only acquires part of the transaction record and a scale-out throughput could be achieved, which we call "spontaneous sharding".
The HPlane IoT framework abstracts security and privacy concerns of critical IoT infrastructure in a Remote Healthcare Monitoring (RHM) environment. Despite its usefulness, the framework lacks a scalable access control mechanism leading to performance and scalability challenges. Some of these challenges can be overcome by using Byzcoin blockchain that provides strong consistency guarantee. However, we found limitations in Byzcoin with respect to reliability, performance and high failure probability due to the use of unreliable Collective Cosigning (CoSi) protocol. Our practical analysis shows that on an average 10-30% CoSi protocols fail when it uses a spanning tree topology to scale Schnorr multisignature. Thus use of Byzcoin poses a significant risk to critical IoT infrastructure. In this paper, we present a robust spanning tree topology along with an implementation of BLS multisignature. Our enhanced topology successfully tackles reliability limitation while BLS multisignature improves performance and lowers failure probability. This work also summarizes how blockchains can serve as a controller application to provide an effective scalable access control in HPlane IoT framework.
This chapter provides a high-level overview of the Ethereum blockchain. The blockchain is an ordered series of blocks, each of which is an ordered series of transactions. A transaction runs on the Ethereum Virtual Machine and executes code that modifies the state tree. We will explore each of these concepts in more detail in the following sections.
A proof system is a protocol between a prover and a verifier over a common input in which an honest prover convinces the verifier of the validity of true statements. Motivated by the success of decentralized cryptocurrencies, exemplified by Bitcoin, the focus of this thesis will be on proof systems which found applications in some sustainable alternatives to Bitcoin, such as the Spacemint and Chia cryptocurrencies. In particular, we focus on proofs of space and proofs of sequential work. Proofs of space (PoSpace) were suggested as more ecological, economical, and egalitarian alternative to the energy-wasteful proof-of-work mining of Bitcoin. However, the state-of-the-art constructions of PoSpace are based on sophisticated graph pebbling lower bounds, and are therefore complex. Moreover, when these PoSpace are used in cryptocur- rencies like Spacemint, miners can only start mining after ensuring that a commitment to their space is already added in a special transaction to the blockchain. Proofs of sequential work (PoSW) are proof systems in which a prover, upon receiving a statement χ and a time parameter T, computes a proof which convinces the verifier that T time units had passed since χ was received. Whereas Spacemint assumes synchrony to retain some interesting Bitcoin dynamics, Chia requires PoSW with unique proofs, i.e., PoSW in which it is hard to come up with more than one accepting proof for any true statement. In this thesis we construct simple and practically-efficient PoSpace and PoSW. When using our PoSpace in cryptocurrencies, miners can start mining on the fly, like in Bitcoin, and unlike current constructions of PoSW, which either achieve efficient verification of sequential work, or faster-than-recomputing verification of correctness of proofs, but not both at the same time, ours achieve the best of these two worlds.
The blockchain is decentralized network system that verifies the validity of the transaction through the consensus of the verifiers without trusted third parties. This mechanism ensures transaction integrity disclosing transaction information transparently. Therefore, it is emerging as the core technology of the 4th industrial revolution by improving reliability and efficiency with features of decentralization, ensuring the integrity, and economic cost reduction. However, there are some problems with the growth of the blockchain. The popularly used PoW (Proof of Work) consensus algorithm applied to the public blockchain requires the price to be compensated in order to agree on the validity of the transaction. This has the disadvantage that the system doesn't operate without compensation. Also, the BFT (Byzantine Fault Tolerance) Algorithm using private blockchain has a limited number of acceptable malicious users. In this case, if the users collude with malicious and exceed the limited number, the transaction is rejected. In this paper, we propose a Smart Manager System and RMBC-DBFT (Randomized Mesh Blockchain Diversity of opinion BFT) enables the safe transaction to the problems above.
The latency and throughput of blockchain-based cyrptocurrencies is a major concern for their suitability as mainstream currencies and as transaction processors in general. The prevalent proof-of-work scheme, exemplified by Bitcoin, is a deliberately laborious effort: the time and energy required to mine blocks makes the blockchain virtually immutable and assists in the consensus-reaching process. Coinspermia (coin=money + spermia=seed) is a different approach: transactions are concurrently seeded throughout a network of peer nodes to an extent sufficient to achieve a high reliability of essential currency operations, including the fast transfer of coins from an owner to a recipient, and the prevention of double spending. A number of Bitcoin features are retained in Coinspermia, including transaction input-outputs and cryptographic addresses and signing, but no special proof-of-work is required to commit transactions. Instead, a client can be assured of an operation completion when a quorum of network nodes acknowledge the operation, which can occur before a transaction operation finishes propagating through the network. Simulation substantiates improved latency and throughput.
Giovanni Ciatto, Roberta Calegari, Stefano Mariani, Enrico Denti · 5 authors
The blockchain is a novel approach to support distributed systems enabling a common, consistent view of a shared state among distributed nodes. There, smart contracts are computer programs that allow users to deploy arbitrary computations, in charge of automatically regulate state transitions and enforce properties. In this paper we speculate on how the blockchain and smart contracts could take advantage of a logic programming approach, and, complementarily, on how logic programming can benefit from the blockchain infrastructure. Accordingly, we discuss some possible research directions and open questions for future research.
Imre Kocsis, Attila Klenik, András Pataricza, Miklós Telek · 6 authors
Timeliness and throughput critical applications require a framework offering predictable temporal characteristics. The best practice for estimating a prediction of the system dynamics relies on benchmarking. Each novel middleware solution needs such an evaluation as part of the development process to assure an appropriate throughput in the future use. General purpose blockchain frameworks are viable replacements for many current systems in several sectors by providing a fully distributed, secure, and non-repudiable ledger as a service. Blockchain technologies target domains with a large number of interactions, thus demanding strict performance guarantees. Engineering for performance targets in a trustworthy manner requires performance models. However, performance characteristics of blockchain systems are highly unexplored due to the novelty of the technology. This paper proposes a general-purpose, systematic methodology for the performance analysis of complex systems, aided by a component-in-the-loop approach. The Linux foundation-hosted hyperledger fabric serves as a case study for the presented methodology.