http://blog.cryptographyengineering.com/2012/05/how-to-choose-authenticated-encryption.html >Given all these great features, you might ask: why does everyone hate GCM? In truth, the only people who hate GCM are those who've had to implement it. You see, GCM is CTR mode encryption with the addition of a Carter-Wegman MAC set in a Galois field. If you just went 'sfjshhuh?', you now understand what I'm talking about.