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I was wondering the security of such documents. Documents like letters written by the British generals to each other communicating about their next battle tactic against the Americans. See this link: http://www.clements.umich.edu/exhibits/online/spies/index-clinton.html

My question is, how advance were the encoding methods back then used to send important information so it doesn't get into the wrong hands? Also, sometimes a message may be sent as a trap with the intentions of purposely fooling the enemy into thinking something else. How would one today figure out if that was true or not looking at them today? What about the intelligence back then? They relied solely on these documents to figure out stuff.

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For reference, see the Two Generals Problem – T.E.D. Feb 21 '14 at 15:20
Armies never rely solely on documents and letters captured from the enemy. They also watch the movements, analyze gossip from the troops and so on. – Oldcat Feb 21 '14 at 19:47
A good overview answer to this question exists here: brainpickings.org/index.php/2012/02/28/invisible-ink – Pieter Geerkens Feb 22 '14 at 15:31

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