Encryption isn't really banned. You can still speak in code. It's just that automated encryption fills airways with private noise.
No, you can't. Other than one very narrow exception, you cannot use "codes or ciphers that hide the meaning of a message". (The exception is for transmitting control commands to a radio-controlled craft or space station.)
And how do hams share information that should be private, like a bitcoin wallet's private key? How do you shell in to the admin interface of a remote tower? You just don't, over amateur radio?
Other than that: right, you just don't. Hams share information that should be private via other communication mechanisms; amateur radio is public.
Gave examples of using PGP cleartext signatures and Cram-MD5 (shudder) challenge-response for authentication without obscuring the meaning of the communication. At the time I thought that IPSEC with Authentication, but Encryption may be the best thing, but that has been slow to take off altogether.