Self-signed in this context basically means "signed by something else than a trusted CA", not the strict meaning of signing a certificate by itself. There are

Self-signed in this context basically means "signed by something else than a trusted CA", not the strict meaning of signing a certificate by itself. There are two elements to public key crypto: The encryption itself (which is perfectly fine on a self-signed cert) and certificate distribution (for which the best current solution are the globally trusted CAs). If you can somehow guarantee that your attacker can only listen to your data, not inject himself as a MITM, self signed is perfectly adequate to protect yourself. The catch is that providing this guarantee is very difficult.