1. A method comprising: receiving, at a mobile device, input from different types of entropy sources; determining, by the mobile device, past entropy using one or more previously generated random numbers by the mobile device using previously received input from the different types of entropy sources; selecting, at least one entropy source from the different types of entropy sources received at the mobile device, based on a comparison between an entropy threshold and the past entropy; generating, by the mobile device, a random number using the input from the at least one entropy source and the past entropy.