Blockchain and Structural Relationship Based Access Control for IoT: A Smart City Use Case Smart city is one of the major Internet of Things (IoT) applications and has become an emerging paradigm with the recent advancements of IoT devices and sensors. But the heterogenous nature of a smart city IoT environment makes it vulnerable to many privacy and security concerns and introduces significant challenges for access control of IoT resources especially where access needs to be provided to third parties and external organizations. This paper proposes a new structural relationshipsbased access control (SRBAC) model that can be used to delegate resource access rights to users in a large scale IoT scenario like smart city while keeping the resource owner in full control. The proposed architecture uses smart contracts and public blockchain for managing access control for external users and a local offblock chain storage for managing access control for organizationxe2x80x99s internal users and enforcing finegrained access control for the resources.

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.