The easiest introduction I've seen is the Alice and Bob example in this paper, http://www.nature.com/nature/journal/v510/n7506/full/nature13457.html http://www.

The easiest introduction I've seen is the Alice and Bob example in this paper, http://www.nature.com/nature/journal/v510/n7506/full/nature13457.html http://www.nature.com/nature/journal/v510/n7506/full/nature1... Plus the paper itself was pretty interesting