NavList:

Brad Morris, you wrote:
"1) I buy my NA directly from the government publishing office. Others may do so too. Awfully hard to break that chain of custody at the Post Office to my door."

There are several alternatives here. First, that chain of custody breaks as soon as it's in your hands. All I have to do is pay someone to go aboard your vessel and swap it out. Maybe a pre-race safety inspection? Or, for a more stand-off solution, you mail a second Nautical Almanac, in identical packaging, with a nicely printed letter explaining that the previously mailed almanac should be set aside and marked "Not for Navigation" (please affix the labels included with this letter!) due to a software error in the compilation process which resulted in printed values for the Moon's HP being frequently in error by as much as one minute of arc (or similar con game language). Think about it... if you received a second Nautical Almanac from the government printing office (with no possible way for you to detect that it is NOT from that source), would it even occur to you to question it? Would a typical ocean sailor have any reason whatsoever to be suspicious of such a package?

And you wrote:
"2) Suppose you did have a bogus Nautical Almanac. You would get 'unusual' results, which may cause you to compare your NA with others, leading to discovery."

Well THAT, Brad, is the whole point of the challenge. :) Could you arrange the fraudulent almanac data so that results would not be unusual in any easily detectable way? I think the answer is yes, though there are some limitations. The case I proposed is probably the most extreme spoofing of celestial navigation that could be achieved. When I set this up, I originally considered spoofing our racing yachts to the Marquesas. But that's too easy. And then again, I almost certainly could not spoof them into a great big circle that brings them to Oahu instead of Tahiti (or could I??).

I don't really understand your point "3".

You also wrote:
"4) Of course, you say, it could be right at the start of the trip and meander away from the truth incrementally until at the end it was significantly wrong. While feasible, its just not practical for pirating or for military purposes, ala GPS spoofing."

Well, it's feasible and "practical" to the extent that it could be done. The real reason it's not literally practical is because NO ONE navigates by celestial navigation except for challenge and pleasure. There are no targets! I had a great conversation with a guy a couple of weeks ago who did a solo circumnavigation. He said he would occasionally spend days using only celestial navigation. But it was for the challenge and the distraction. So that basically limits us to yachts and ONLY yachting crews, like in my contrived setup, that have clearly announced that they would not "cheat" and use satellite navigation. Are there any yachts worth misdirecting? Criminals go after yachts, but they're relatively easy to grab without navigational spoofing. So that leaves the entertainment value of "hacking" (making the rich and powerful look foolish is an ancient tradition). That's really the only way that I could imagine anyone actually trying this. The practical case if not the point, of course. The point is that any navigational method that involves external signals can be spoofed. Only inertial navigation is immune. And then, of course, we could consider history. Why didn't anyone "spoof" celestial navigation historically? Did it simply not occur to anyone?

You concluded:
"How about spoofing the time signal? Just provide a stronger radio time check than the real one at the appropriate frequency (to swamp the true signal) and shift the time. That will do it."

Yes, that would certainly allow you to move the navigation east or west. In fact it would be especially easy to push the navigation east (if I've got the sign right) since you could just record the original signals and re-broadcast them minutes or hours later. But it requires either a nearby vessel transmitting the bogus signal or a powerful transmission station on land somewhere. This would be easily detected and shut down within hours. And the original signals, which are quite strong wouldn't necessarily be masked. A potential target could hear both the real and the false time signals. Historically, were there ever attempts in wartime to shut down time signal transmissions? Finally, on a real racing yacht today, there would be numerous crew members with good watches (as we've discussed recently, even cheap watches are plenty good enough for celestial navigation). Would they all believe that their watches are suffering from the SAME error??

-FER

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