The issue with cryptography is that it’s obvious the message has been encrypted. It will draw interest, even if it’s benign. But there is a way to send encrypted messages so that no one even knows there IS a message, much less that it’s encrypted. Steganography.
Is you are willing to spend a bit of time learning how it works, there are a bunch of different programs you can use – not to hide your messages, but to make them invisible.
I recommend OpenPuff. Hard to learn – hard to beat. Your secrets will stay secret. Of course, it was designed for Windows, so I can’t use it. But I have no secrets and, if I did, I wouldn’t tell them to you.
UPDATE: 30 July, 2016
The FBI claims to have broken this software after having found ‘Russian’ spies (the Chapman group?) using it. The claim is unlikely unless they recovered the sending computer and the passwords. The FBI does not otherwise have that level of sophistication.
However, the NSA does. Still, why they would bother with the Chapman group, except in an effort to uncover a deeper target – which they did not do to my knowledge – seems a huge waste of resources.
One almost has to be a mathematician to understand this clearly, but it has, and continues to defy mid-level attempts to even find it, much less decipher it. You can throw the software away and merely read the thesis if your interest, like mine, is theoretical.