Implementation of Smart Contracts Using Hybrid Architectures with On- and Off-Blockchain Components

Recently, decentralised (on-blockchain) platforms have emerged to complement centralised (off-blockchain) platforms for the implementation of automated, digital (smart) contracts. However, neither alternative can individually satisfy the requirements of a large class of applications. On-blockchain platforms suffer from scalability, performance, transaction costs and other limitations. Off-blockchain platforms are afflicted by drawbacks due to their dependence on single trusted third parties. We argue that in several application areas, hybrid platforms composed from the integration of on- and off-blockchain platforms are more able to support smart contracts that deliver the desired quality of service (QoS). Hybrid architectures are largely unexplored. To help cover the gap, in this paper we discuss the implementation of smart contracts on hybrid architectures. As a proof of concept, we show how a smart contract can be split and executed partially on an off-blockchain contract compliance checker and partially on the Rinkeby Ethereum network. To test the solution, we expose it to sequences of contractual operations generated mechanically by a contract validator tool.Comment: 12 pages, 7 figure

Scalable and Privacy-preserving Design of On/Off-chain Smart Contracts

The rise of smart contract systems such as Ethereum has resulted in a proliferation of blockchain-based decentralized applications including applications that store and manage a wide range of data. Current smart contracts are designed to be executed solely by miners and are revealed entirely on-chain, resulting in reduced scalability and privacy. In this paper, we discuss that scalability and privacy of smart contracts can be enhanced by splitting a given contract into an off-chain contract and an on-chain contract. Specifically, functions of the contract that involve high-cost computation or sensitive information can be split and included as the off-chain contract, that is signed and executed by only the interested participants. The proposed approach allows the participants to reach unanimous agreement off-chain when all of them are honest, allowing computing resources of miners to be saved and content of the off-chain contract to be hidden from the public. In case of a dispute caused by any dishonest participants, a signed copy of the off-chain contract can be revealed so that a verified instance can be created to make miners enforce the true execution result. Thus, honest participants have the ability to redress and penalize any fraudulent or dishonest behavior, which incentivizes all participants to honestly follow the agreed off-chain contract. We discuss techniques for splitting a contract into a pair of on/off-chain contracts and propose a mechanism to address the challenges of handling dishonest participants in the system. Our implementation and evaluation of the proposed approach using an example smart contract demonstrate the effectiveness of the proposed approach in Ethereum

Constructing privacy aware blockchain solutions: design guidelines and threat analysis techniques

Blockchain is an incipient technology that offers many strengths compared to traditional systems, such as decentralization, transparency and traceability. However, if the technology is to be used for processing personal data, complementary mechanisms must be identified that provide support for building systems that meet security and data protection requirements. In this work we study the integration of off-chain capabilities in blockchain-based solutions, moving data or computational operations outside the core blockchain network. Additionally, we develop a thorough analysis of the European and Uruguayan data protection regulation and discuss the weaknesses and strengths, regarding the security and privacy requirements established by that regulation, of solutions built using blockchain technology. Based on this analysis, we present a system architecture for the design of privacy aware solutions that are built using blockchain technology. We also put forward a systematic approach for performing a security and privacy threat analysis of such kind of solutions. Finally, we illustrate the use of the proposed methodological tools, presenting and discussing both the design and the security and privacy assessment of a system that provides services to handle, store and validate digital academic certificates.Blockchain es una tecnología incipiente que ofrece muchas fortalezas en comparación con los sistemas tradicionales, como la descentralización, la transparencia y la trazabilidad. Sin embargo, si se va a utilizar esta tecnología para el procesamiento de datos personales, se deben identificar mecanismos complementarios que brinden soporte a los sistemas de construcción que cumplan con los requisitos de seguridad y protección de datos. En este trabajo estudiamos la integración de capacidades de soluciones offchain en soluciones basadas en blockchain, moviendo datos u operaciones computacionales fuera de blockchain. Adicionalmente, desarrollamos un análisis exhaustivo del reglamento europeo y uruguayo de protección de datos personales y discutimos las debilidades y fortalezas, en cuanto a los requisitos de seguridad y privacidad que establece dicho reglamento, de las soluciones construidas con tecnología blockchain. En base a este análisis, presentamos un marco metodológico para el diseño de soluciones basadas en tecnología blockchain, pensando en la privacidad. También presentamos un enfoque sistemático para realizar un análisis de amenazas a la seguridad y la privacidad de este tipo de soluciones. Finalmente, ilustramos el uso de las herramientas metodológicas propuestas, presentando y discutiendo tanto el diseño como la evaluación de seguridad y privacidad de un sistema que brinda servicios para manejar, almacenar y validar certificados académicos digitales