Green computing has become a growing trend in computing, pursuing the goal of helping software developers to pay more attention to produce energy-effiency software. This is specially relevant for battery-powered mobile applications, where minimizing the energy consumption is required to both mitigate the greenhouse effect and to extend the battery lifetime. In this paper we analyze the energy consumption of cryptographic primitives in Android devices. Our ultimate goal is to help Android application developers, especially those who are not experts on security, to choose the most energy efficient cryptographic algorithms considering different security providers and different security transformations. We have performed our experiments using an energy profiling tool based on the PowerTutor application. Our results show that this type of energy efficiency studies are necessary, because selecting the most energy efficient configuration depends on many factors, and some of the conclusions are not so obvious.