Saving energy is one of the most challenging aspects in the wireless network devices. Such devices are connected together to perform a certain task. A well-known example of these structures is the Wireless Sensor Network (WSN). Distributed WSN consists of several spread nodes in a harsh area. Therefore, once network has been established sensors replacement is not a possible option before at least five years which called network lifetime. So, it is a necessity to develop specific energy aware algorithms that could save battery lifetime as much as possible. Security and Privacy are the vital elements which need to be addressed to hold up to the trust of users in WSN environment. Because the majority of modern cryptographic algorithms were designed for desktop/server environments, many of these algorithms cannot be implemented in the constrained devices used by these networks. Symmetric key algorithms are a typically efficient and fast cryptosystem, so it has significant applications in many realms. For a WSN with constraint computational resources, the cryptosystem based on symmetric key algorithms is extremely suitable for such an agile and dynamic environment. Therefore, a Simple Lightweight Encryption Algorithm (SLEA) based on addition and subtraction operations and compact Substitution-boxes (S-boxes) is proposed for wireless networks due to its low energy consumption, simple hardware requirements and suitable level of security. In addition, the algorithm tries to overcome the limitations of both public- and symmetric-key protocols. It relies on a smart version of Feistel structure.