[Taqwus]

To a limited degree... An attack fleet deep in enemy territory is largely on its own; the fact that communications and reinforcements would both take massive amounts of time due to distance implies a greater degree of autonomy, and I'm not convinced that one fleet would necessarily be aware of the disposition of other fleets that aren't in the same general area. On the other hand, they will likely have information about that particular region.

In addition, any society that can travel between star systems probably has better computing technology, which would allow for such things as the use of OTPs specific to a link in a hierarchy, or alternately strong public-key cryptography or other methods by which compromising one link might not affect others... that is, the "universal code book" vulnerability wouldn't necessarily exist.

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-- The thing that goes bump in the night