Here is a rough diagram which demonstrates it http://www.2uo.de/myths-about-urandom/structure-yes.png http://www.2uo.de/myths-about-urandom/structure-yes.png (f

Here is a rough diagram which demonstrates it http://www.2uo.de/myths-about-urandom/structure-yes.png http://www.2uo.de/myths-about-urandom/structure-yes.png (from the detailed page http://www.2uo.de/myths-about-urandom/ http://www.2uo.de/myths-about-urandom/). /dev/random will block when the entropy estimate in low, but in a practical sense, the output of /dev/urandom and /dev/random are both random.