Extropians just assume that good networks will be there. Here's some engineering.
A Distributed, Decentralised Information Storage and Retrieval System: http://www.dcs.ed.ac.uk/~iic/4yp/
A Practical Security System for Ad-Hoc Networks: http://www.cl.cam.ac.uk/~fms27/duckling/
A useful site for news about cryptography, privacy and communication: http://jya.com/crypto.htm