Embedded systems are the combination between hardware and software designed to perform some specifics functions. An embedded system is generally a part of a larger system that uses a computer network to communicate with other devices. For this reason, secure communicaartion is of great importance to guantee the confidentiality of the transmitted information, which can be provided by using encryption algorithms. The security is usually not a requirement when designing an embedded system, causing few techniques to be implemented for the security of these devices. This paper presents an evaluation of run-time performance of AES using a cryptography library developed for embedded systems, called Relic in a communication between two process in a general purpose computer, between a general purpose computer and a embedded system and between two embedded systems. It is considered the key sizes supported by the algorithm, the size of the transmitted data and the architecture used, also measuring the relation of the time spent by encryption and decryption and the total time for the secure communication. The results demonstrated that the architecture has a greater impact on the encryption and decryption times along with the message sizes. However, even for the communication between embedded systems, the percentage of the encryption and decryption time on the entire secure communication is smaller than 14%.