Comment by tialaramex

The communication is clearly inflected by Usenet conventions, but I think that's as forgiveable as the choice to have Banks' Culture starships named using our cultural references like "Just read the Instructions" or "Don't Try This At Home". I don't think we're told it actually is Usenet -- it's just that necessarily light speed comms is very slow compared to the pace of life at this scale so it will feel much like Usenet. So I actually thought this made lots of sense.

It's true that we have no apriori justification for the existence of symmetric cryptography and so in principle somebody might have a constructive proof that you can't do this at all and we're boned. There was no evidence for this when the book was written and there's no evidence for it now, but it's nowhere close to as crazy as the Zones of Thought physics so, sure.