Internet of Things (IoT) is a paradigm shift towards digital world. To make this scenario better, we delve into the capabilities of IoT to perform Complex Event Processing (CEP) in a secured manner. In this paper, we discuss the functioning of IoT framework to perform CEP on multiple sensor values and make sure that adversaries are not able to tamper our code. Existing implementations of CEP engines do not accommodate changes in rules or addition of new rules. This research aims to implement a framework for such a CEP engine, which allows dynamic updation of rules. This is achieved by designing a new, flexible approach for representing rules and annotating data within the system, and also a standard messaging protocol that IoT nodes have to use. We also add a novel feature to provide security using side-channel information collected through FLUSH and RELOAD method.