Decentralized authorization in constrained IoT environments exploiting interledger mechanisms Abstract   We present models that utilize smart contracts and interledger mechanisms to provide decentralized authorization for constrained IoT devices. The models involve different tradeoffs in terms of cost, delay, complexity, and privacy, while exploiting key advantages of smart contracts and multiple blockchains that communicate with interledger mechanisms. These include immutably recording hashes of authorization information and policies in smart contracts, resilience through the execution of smart contract code on all blockchain nodes, and cryptographically linking transactions and IoT events recorded on different blockchains using hashlock and timelock mechanisms. In the case of two ledgers, an authorization and a payment ledger, the authorization ledger can be a private Ethereum network or a permissioned ledger such as Hyperledger Fabric. For decentralized authorization where a subset of moutofn authorization servers are required, we present two policies for selecting the    m    servers. The first policy can utilize statistics of the authorization servers such as transaction cost and response time. The second policy selects the first    m    servers that respond. The proposed models are evaluated on the public Ethereum testnets Rinkeby and Ropsten, and for different implementations on the Hyperledger Fabric permissioned ledger, in terms of execution cost (gas), delay, and reduction of data that needs to be sent to the constrained IoT devices.

Communication Aspects of the Integration of Wireless IoT Devices with Distributed Ledger Technology The pervasive need to safely share and store information between devices calls for the replacement of centralized trust architectures with decentralized ones. DLTs are seen as the most promising enabler of decentralized trust, but they still lack technological maturity, and their successful adoption depends on the understanding of the fundamental design tradeoffs and their reflection in the actual technical design. This work focuses on the challenges and potential solutions for an effective integration of DLTs in the context of the Internet of Things (IoT). We first introduce the landscape of IoT applications and discuss the limitations and opportunities offered by DLTs. Then we review the technical challenges encountered in the integration of resourceconstrained devices with distributed trust networks. We describe the common traits of lightweight synchronization protocols, and propose a novel classification rooted in the IoT perspective. We identify the need for receiving ledger information at the endpoint devices, implying a twoway data exchange that contrasts with the conventional uplinkoriented communication technologies intended for IoT systems.