Green computing is a growing trend in computing, pursuing the goal of helping software developers to be more aware and produce energy-efficient software. This is especially relevant for battery-powered mobile applications, where a minimal energy consumption is desired to both mitigate the greenhouse effect and extend the battery lifetime. In this paper, we analyze the energy consumption and execution time of cryptographic primitives in Android devices. Our ultimate goal is to help Android application developers, especially those who are not experts in security, to choose the most energy-efficient cryptographic algorithms considering different security providers and security transformations. Information to make a tradeoff between energy and time consumption is also provided, being especially useful when the differences in energy consumption of different alternatives are not so significant. We have conducted our experiments with an energy profiling tool based on the PowerTutor application, which has been adapted to automate the energy profiling. Our results show that this type of power consumption studies is necessary, because selecting the most energy-efficient configuration depends on many factors, and some of the choices are not obvious to developers.