Smart environments are part of the rapid development of digital transformation, and the growing need for multiple connections with different devices is driving research attention toward the Internet of Things (IoT) as a way of communicating with objects. Data transmitted widely and openly, whether in industries, homes, buildings or cities, is vulnerable to attacks that capture private information or even control devices without proper protection measures. Therefore, secure communication is mandatory to ensure an efficient and reliable system, as well as the application methods, must be updated to anticipate the advance of attacks. Thus, the Rivest-Shamir-Adleman (RSA) asymmetric encryption method, which is widely, is taken as a basis to compare the application in IoT systems of a lightweight cipher (algorithm), using Elliptic Curve Cryptography (ECC) which requires smaller key sizes to match the security level of RSA.