Internet of Things (IoT) embraces the interconnection of identifiable devices that are capable of providing services through their cooperation. The cooperation among devices in such an IoT environment often requires reliable and trusted participating members in order to provide useful services to the end user. Consequently, an IoT environment or space needs to evaluate the trust levels of all devices in contact before admitting them as members of the space. Existing trust evaluation models are

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... ased on resources such as historical observations or recommendations information to evaluate the trust level of a device. However, these methods fail if there is no existing trust resource. This paper introduces a specific IoT environment called personal space IoT and proposes a novel trust evaluation model that performs a challenge-response trust assessment to evaluate the trust level of a device before allowing it to participate in the space. This novel challenge-response trust assessment model does not require the historical observation or previous encounter with the device or any existing trusted recommendation. The proposed challenge-response trust assessment model provides a reliable trust resource that can be used along with other resources such as direct trust, recommendation trust to get a comprehensive trust opinion on a specific device. It can also be considered as a new method for evaluating the trust value on a device.