Recently, there has been a great interest in connecting all things (objects) together anywhere and anytime on the Internet, which today is known as the Internet of Things (IOT). The IOT architecture is made up of different layers, and each layer is subject to different attacks / threats. On the other hand, there are several security measures in place to counter these attacks. Cryptography algorithms are one of the most important security measures to counter these attacks. In this paper, several potential attacks on IoT devices are described. A comprehensive study of the most important cryptography algorithms (symmetric-key, asymmetric-key and Lightweight) was made, with an explanation of the mathematical background of them