Regarding sharing a password/access/secret to someone... and then you don't have control whether they will also share this on, and potentially it could/will end up publicly known, thus insecure.
The term I am looking for is along the lines of "chinese whispers" but that means "the message gets more distorted"... I want the phrase depicting that a recipient can potentially just keep sharing the secret down a chain:
Okay Joe: Hicsy said this password is really secret so just type it once and forget it.
Hi Marie, I shouldn't even have this password so, i'm only sharing it just this once to you + Sue
Hi guys, here's that password that you use to unlock devices in evidence room.