Comms

    [gef] I wonder how facebook would react if you'd send message
          back and forth on their platform, but manually encrypt
          all messages

In theory you could have two people who share a unique language, in which case Facebook (may) not be able to extract the usual from the content of the messages. This language in cryptography goes by the name "one time pad" which has the same problem as a unique language shared by only two people: that of getting that unique language only to that one other person. There is also the metadata problem, in that Facebook knows who is messaging whom when. Possibly this could be worked around, somewhat, by delaying and batching the messages, which might raise the simple point of why not not use Facebook?

Elsewhere, ham radio in particular, encryption is in theory disallowed. The following is for Shamblestown, U.S.A.; if elsewhere, check your local rules and regulations.

(b) Where authorized by §§ 97.305(c) and 97.307(f), a station may transmit a RTTY or data emission using an unspecified digital code, except to a station in a country with which the United States does not have an agreement permitting the code to be used. RTTY and data emissions using unspecified digital codes must not be transmitted for the purpose of obscuring the meaning of any communication. When deemed necessary by a Regional Director to assure compliance with the FCC Rules, a station must:

(1) Cease the transmission using the unspecified digital code;

(2) Restrict transmissions of any digital code to the extent instructed;

(3) Maintain a record, convertible to the original information, of all digital communications transmitted.

In practice there remain various means of sending coded messages—one if by sea, two if by land—or one might resort to the Agony Column (no, it does not involve CSS).

Others might try stenoesaurogophy, or the art of disguising your writing on a steganosaurus.