Concur that PK is probably inappropriate, but not necessarily that this means PCQ would be (irrelevant). The Voynich manuscript is likely a despairingly poor

Concur that PK is probably inappropriate, but not necessarily that this means PCQ would be (irrelevant). The Voynich manuscript is likely a despairingly poor example of any argument, but it's the most famous long-lived / unresolved encoded text I could think of. (I think a year or two there was a claim it was properly decrypted but I'm not convinced it ever will be, mostly because I suspect it wasn't ever meant to make sense.) Back to the key rotation question - I think we agree that's not a necessary requirement.