The rapid growth of information and communication systems in recent years has brought with it an increased need for security. Meanwhile, encryption, which constitutes the basis of the majority of security schemes, may imply a significant amount of energy consumption. Encryption algorithms, depending on their complexity, may consume a significant amount of computing resources, such as memory, battery power and processing time. Therefore, low energy encryption is crucial, especially for battery powered and passively powered devices. Thus, it is of great importance to achieve the desired security possible at the lowest cost of energy. The approach advocated in this thesis is based on the lack of energy implication in security schemes. It investigates the optimum security mode selection in terms of the energy consumption taking into consideration the security requirements and suggests a model for energy-conscious adaptive security in communications. Stochastic and statistical methods are implemented – namely reliability, concentration inequalities, regression analysis and betweenness centrality – to evaluate the performance of the security modes and a novel adaptive system is proposed as a flexible decision making tool for selecting the most efficient security mode at the lowest cost of energy. Several symmetric algorithms are simulated and the variation of four encryption parameters is examined to conclude the selection of the most efficient algorithm in terms of energy consumption. The proposed security approach is twofold, as it has the ability to adjust dynamically the encryption parameters or the energy consumption, either according to the energy limitations or the severity of the requested service.