I had the same question until I realised it meant Google Cloud Messaging (or, this is how people seem to interpret it) - my initial thought was that it was abou

I had the same question until I realised it meant Google Cloud Messaging (or, this is how people seem to interpret it) - my initial thought was that it was about Galois Counter Mode (an authenticated encryption mode), and was curious why not using it was considered a benefit. Threema does seem to use XSalsa20 + Poly1305 for authenticated encryption (not AES in GCM), btw.