Perhaps the pass-phrase would not be discovered, but a record of it could be found after Luthor's arrest.
Picture talking heads, a news anchor and a LexCorp PR flack defending Luthor, exposing the pass-phrase on live TV only to have everyone and their brother now opening the message and hearing
“Hello, Superman, Lex Luthor here. I wanted to thank you for saving the planet for me. You should know that LexCorp built your survival suit. In fact, I personally helped in the design. From the instant your guidance system signaled that you were no longer needed, your air supply has been laced with Kryptonite and poison gas. You were a worthy adversary, but I always win. Have a nice death. Oh, I’ll be sure to be there to comfort Lois Lane when you’re gone.”
