28 TH INTERNATIONAL CONFERENCE ON INFORMATION SYSTEMS DEVELOPMENT (ISD2019 TOULON, FRANCE) Secret Smart Contracts in Hierarchical Blockchains Sînică Alboaie Faculty of Computer Science, Alexandru Ioan Cuza University, Axiologic Research and RomSoft Iasi, Romania salboaie@gmail.com Lenuța Alboaie Faculty of Computer Science, Alexandru Ioan Cuza University Iasi, Romania adria@info.uaic.ro Zeev Pritzker Arteevo Tel Aviv, Israel zeev@arteevo.com Adrian Iftene Faculty of Computer Science, Alexandru Ioan Cuza University Iasi, Romania adiftene@info.uaic.ro Abstract This article presents the results of an implementation of a new platform based on swarm communication and executable choreographies. In our research of executable choreographies, we have come up with a more general model to implement smart contracts and a generic architecture of systems using hierarchical blockchain architecture. The novel concepts of secret smart contract and near-chain are introduced. The near-chain approach presents a new method to extend the hierarchical blockchain architecture and to improve performance, security and privacy characteristics of general blockchain-based systems. As such, we are subsequently defining and explaining why any extension of blockchain architectures should revolve around three essential dimensions: trustlessness, non- repudiation and tamper resistance. The hierarchical blockchain approach provides a novel perspective, as well as establishing off-chain storages (near-chains) as special types of hierarchical blockchains stored in a distributed file system. Furthermore, we are providing solutions to the difficult blockchain concerns regarding scalability, performance and privacy issues. Keywords: Executable choreography, Swarm communication, Choreographic smart contract, Secret smart contracts, Time-locked smart contracts, Hierarchical blockchains, Data self-sovereignty. 1. Introduction Blockchain technologies are contributing to transformative changes in business and society. The exponential increase in the Bitcoin price in the last five years created a massive wave of interest in research of blockchain related technologies such as the smart contracts [24]. Blockchain enables new types of innovation processes and offers opportunities for disintermediating network services resources. Blockchain technologies can also potentially increase transparency and citizens’ participation in democratic processes. To create a real impact, this technological evolution must be accompanied by features that enhance trust and transparency. Guaranteeing transparency, trust, and respect for