Re: coding and encryption
One would also note cable TV is often encrypted, as are military satellites. The main barrier is the time of decryption, which can be a long time with RSA for example, but fairly quick with blowfish. I have designed a few encryption codes myself and while perhaps not unbreakable it is fairly easy to make something very hard to crack. The figures we see of times to crack a code assume we know the encoding algorithm which we wouldn't with an alien signal.
It is trivial to design an encryption code that would take 10 e 300 years to crack, 1 followed by 300 zeroes.