The development of Internet of Things (IoT) has granted multiple interoperable features for user to digital things communication. The future communication technology and service provisioning in IoT is large scaling an open environment. The large scale IoT environment is supported by sensor network and independent nodes. The intelligent computing, storage, and computation features of the nodes are inherited by the IoT paradigm for its application and service support. In such an open environment, security is a prominent issue that must be administered in a decentralized manner. In this manuscript, a decentralized and scalable security framework for future IoT is designed. This framework exploits the advantages of intelligent computing and tree-based hash for device and request authentication to provide device-to-device security. The tree-based hash is used for authenticating requests and the central authority-based security feature of the framework provides device level security, ensuring better privacy and integrity in communications. The experimental analysis of the proposed security framework is analyzed in terms of detection rate, communication loss, disconnection ratio, and delay. 1 INTRODUCTION Internet of Things (IoT) has emerged as an advanced technology in the recent years of communication field incorporating diverse networks, applications, and services. The concept of IoT is to integrate communicating "things" and human users as a single entity through digital medium. It is capable of visualizing real-time components, data, and information as a digital perspective for distributed access, communication, and sharing. 1 Heterogeneous networks, long-and short-range communication infrastructures, multilevel protocols, applications, and services are present in IoT for pervasive access. This eases interaction between devices, data sharing, uninterrupted communication, resource management, storage, and access for end-users demanding reliable service quality. 2 End-users initiate queries through requests that are processed at different IoT platforms including cloud and gateways. Distributed resources are migrated toward end-user devices through applications boasted for services. Extended network functions such as complex computations, system analysis, storage, and retrieval are performed with the support of heterogeneous service providers. A notable heterogeneous service provider is cloud platform that is capable of strengthening the ubiquitous access and multilevel device interaction of the end-users. 3 The "things" connected in an IoT environment includes short range static devices such as RFIDs to mobile smart devices such as IoT vehicles. The smart nature of the devices is exploited by augmenting sensor-based battery powered circuits that serves the communication purpose. With the equipped electronic circuits, the device is capable of participating in external communication and joining heterogeneous network. Wireless sensor network (WSN) is a renowned technology