Any civilization sufficiently advanced enough to radiate signals is also going to be sufficiently advanced to encrypt their communications. We could be pulling in all sorts of alien communications right now. Since the best encryption makes its signal indistinguishable from noise, there's no way that we are going to know that it's there.

It's happening to our civilization already. For example, the Nintendo DS that my kids play with uses RSA encryption for PictoChat.

Now here's a thought:

If alien signals are encrypted and we do manage to decrypt them, could we find ourselves faced with an inter-planetary lawsuit for unpaid royalties...?

Hold on a minute Graham...are you saying we might be able to get future episodes of Battlestar Galactica live from the scene of the action? And we just need the intergalactic edition of DVDdecrypter to be able to view them? I knew there had to be a way around Sky stiffing us Virgin Media customers!

Yup .. the alien equivalent of the riaa / mpaa would be

all over us ,sending hordes of lawyers in flying saucers

to file lawsuits for recording their broadcasts ..

errr .. wait ..

That does explain the timing of Area 51 activity with the

experiments of Penzias and Wilson recording the background radiation ..

Area 51 was/is nothing more than the place where the US got and

still gets rid of hordes of alien attorneys landing on their soil ; )

Now that we got this all figured out .. it's breakfast time ..

"Now here's a thought:

If alien signals are encrypted and we do manage to decrypt them, could we find ourselves faced with an inter-planetary lawsuit for unpaid royalties...?"

Only if you attempt to view the decrypted signal on more than one telescope or upload it to Q-bit torrent.

Wouldn't a plain text transmission from an alien basically be "encrypted" to us humans? I mean, once we deduce what they use as a base for their numbering system, and once we discover which of our 5 senses are closest to the one(s) they use for communication, and once we gain some understanding of their cultural setting so we can have the vaguest clue what they might want to talk about, then all that remains is the simple task of figuring out their alphabet and grammar, and then maybe we might actually recognize a signal for a signal... I guess encryption is just one extra step to take!