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I'm looking for historical records showing that parties using coded messages (from the Egyptians to the Romans to actors in the American Civil War, etc) would sometimes stipulate deadlines by which a response must be received. The encoding of messages needs to be by hand (so no computers/machines involved).

I know there is a project to decode thousands of Civil War telegrams, but I have been unable to find a collection of the decoded messages to read. And no history books I've encountered that describe ancient military protocols include a description of deadlines for replies.

The famous Zimmerman Telegram (captured and decoded by the British in WW I) makes an offer to Mexico, but does not appear to have an expiration date attached to it.

Surely if a message is sent to (say) a general in the field and no response is received by some preordained deadline, an action is taken, right? No one will just wait forever?

I would appreciate any examples you know of, or suggestions on where I might look to find examples. I have already reviewed David Kahn's book "The Codebreakers."

Amended to Add: It's fine if the time limit was not explicitly stated in each message as long as it was well-established somehow. For example, if say a Roman War Manual stated that "if no response is received within 3 days, we assume the courier was lost and send another message." That would be enough for my purposes. But I'm unable to find records of such policies in historical records (for military, diplomatic or other secure-messaging settings).

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    What are you looking for? If a cipher is used (i.e. you have a plaintext message, apply some algorithm to it, and you get the ciphered message) then the contents of the message (which include the deadline) is independent of the cipher. A different issue would be if a codebook is used, in that case the codebook would need to include a way to codify the deadline. Also keep in mind that making the message longer means that it takes longer to cipher and decipher. – SJuan76 Mar 18 at 19:17
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    You may wish to read theTwo generals problem and the Byzantine General's Problem (if you haven't already). – MCW Mar 18 at 19:18
  • Also note that the Zimmerman telegram wasn't enciphered, it was encoded. Do you care about the difference for the purposes of this question? – MCW Mar 18 at 19:26
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    I'm simply trying to prove to a colleague that some secret communications commonly had time limits or deadlines for replies, even before the computer era. The type of encryption is unimportant. – Fixee Mar 18 at 19:27
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    That is an interesting question. I suspect that the message window was conveyed through out of band protocols, but I'm going to be fascinated with the answer. I'm a little concerned that it is difficult to prove a negative. – MCW Mar 18 at 19:28

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