If you’re like me, you probably worry that the messages you send will end up in the wrong hands. This post is about the most secure way to send messages, in the US, anyways.
Old fashioned letter
Believe it or not, a good old fashioned letter is the most secure way to send a message. Yes, it’s not encrypted, but it still has the most legal protections. It’s illegal for anyone to read a letter that’s not addressed to them, so chances are, they won’t. Even if they want to, a letter is more or less always under supervision; it’s in a metal box when you send it, and in a locked metal box when it arrives. Also, the government needs a search warrant to read your letters, something that is not required to intercept internet traffic. If you’re worried about the NSA, letters are your best bet.
Need more security?
The only thing I can think of that’s more secure than a plain-text letter, is an encrypted letter. You send your friend a 4096 bit or longer RSA in an SD in the mail, and they send you theirs. Then, using your friend’s public key, send them a long AES key, that will be used to encrypt all messages sent from that point on. Now, as long as the message is encrypted, it’s safe. If it’s intercepted, the person who steals the message can’t do anything, because the only thing being sent is public keys, or already encrypted messages. Now, not only does the government need a search warrant to read your letters, they can’t, because all they’ll find is encrypted gibberish.
Or, you can just write them a note, give it to them in person, and have them burn it after they read it :)
If you can’t
If you can’t send a letter, then GPG is the next best thing, messages are encrypted, signed, and authenticated.