improve coverage and style for crypto/ folder

![screenshot from 2014-12-19 19 34 00](https://cloud.githubusercontent.com/assets/287189/5512152/0d7d9278-87b6-11e4-8e00-3c55985b96fc.png)

(random.js can't be improved because it has some browser-specific code :disappointed: )

There is no change... I only removed the comment, and moved the code a few lines above. I think the comment refers to a possible optimization. Will ping @ryanxcharles about this, to be safe