Can someone please explain the C&C for bots ?
im reading a [paper](http://static.usenix.org/event/leet11/tech/full_papers/Xiang.pdf) about Android bot , and its explaining something called URL flux 
as method of C&C . however i couldn't really get it , so i need to know how normal bots preform c&c so i can understand this .
for example why the bot needs a public key to authenticate commands ? and what the username generator algorithm for ?