I assume you are aware of the forthcoming digital pulse radio technology http://www.time-domain.com/technology.html It is not exactly crypto, but uses ultra-wideband low-power (they claim 10 miles with 500 uW) emissions and pseudo random codes to shift the spike train encoding the information stream. It looks very like white noise. What is your estimate how difficult it would be to screen for such communication channels, and how rapidly could one crack them (assuming no further encryption of the traffic)? -- Eugene Leitl
