If you can't hide the fact that you send a secret message, and you have no secure channel available, then resort to insecure channel, and protect your message by reshaping it so that only a key holder can extract its meaning. Ideally you may want to: Hide the method used to reshape the message (process the plaintext to its ciphertext) -- obscurity Use a method that does not allow the key to be deduced from the ciphertext (equivocation) Otherwise: use a method that would require too much time and effort to deduce the key from the ciphetext (eroding intractability)