I have vivid memories of the authenticated messages, as ATC was required to re-broadcast the words from the "Bomber Box" verbatim.
"This is the Bomber Controller, for BombList ... readiness State ... is now in force, I say again... Authentication.". I had one sgt ATCO who, for some inexplicable reason, would never re-transmit verbatim, despite the exact wording having been written on a perspex plaque pro forma by the assistant and passed to him. He would invariably depart from the script at some point. Endless bollockings failed to cure him. I assume the crews relied on their other sources of information!