Abstract
The popularity of the Internet of Things (IoT) and its various applications are growing rapidly. Trust in most IoT networks is presumed implicitly. This implicit assumption of trust can be abused by adversaries to disrupt the network and manipulate reputations of trusted devices. Spoofing devices' identities or forging new identities allows adversaries to masquerade and act as legitimate devices. Devices with forged identities are known as Sybils. In this paper, we propose an IoT trust model that uses permissioned blockchains that utilize Smart Contracts (executable policies) to evaluate trustworthiness of IoT devices by recording and validating IoT devices' identities to prevent Sybil attacks. Additionally, to show effectiveness of our model, we provide a proof-of-concept prototype of our model's key features.