In terms of research and innovation, the Internet of Things is one of the most promising areas. IoT platforms are taking place in almost every sector, from healthcare to smart cities to smart agriculture. IoT mainly consists of three units’ sensor units, a microcontroller/microprocessor unit, and an actuator. These sensors can generate enormous amounts of data wherever they are deployed to monitor. The transmission of this data is not secure, as there are no defined architectures in IoT until now. The architecture of IoT varies depending on the application it is targeting. In this review article, we have discussed the security of data transmission and various reasons behind the lack of data security in IoT, a model for improving the security-related issues in the IoT, and the importance of cryptography and lightweight cryptography in IoT. This article answers the questions related to the issues faced in securing the data of Internet of Things devices.