History Main / ReadingtheEnemysMail

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* Literature/{{Discworld}}

* So the West couldn't do this, the Soviets used something called "one-time pads". If proper operational security is maintained, and the key is not compromised or re-used,the one-time pad is ''completely uncrackable''. However, when one set got accidentally used twice, the West were able to figure out the messages and from 1946 break a good many of them. It was key to identifying a good number of Soviet moles, including the Rosenbergs and Julius Fuchs. Some people weren't prosecuted as VENONA (as it was called) was too valuable to be used in court- it was not declassified until 1995.

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[[quoteright:627:https://static.tvtropes.org/pmwiki/pub/images/intercept_station.jpg]]
[[caption-width-right:627:An intercept section at MS-1, Vint Hill Farms, Virginia during WWII]]

* The main reason for wanting to attack the titular submarine in ''Film/{{U571}}'' was to capture the submarine's Enigma machine.

* In ''Literature/TheThrawnTrilogy'', eventually the New Republic did figure out that Thrawn was aware of all the plans they made in the Imperial Palace on Coruscant. They spent a lot of effort trying to figure out who the spy is. Only after a slicer cracks Delta Source's transmission encryption on his own time for fun do they figure out that it was a sophisticated listening system HiddenInPlainSight.

* Where British, Germans and Americans cracked the enemy ciphers in UsefulNotes/WorldWarII, the Italians choose an easier way: in September 1941 (when the US were still neutrals), Italian spies broke in the US embassy in Rome and stole the ciphers. From then on, the Italians were able to read the US diplomatic communications without any problem, something that, thanks to the American consul at Alexandria having access to the British war plans from December 1941 and reporting them to Washington, allowed the Axis forces in Africa to know what the British were doing. While the British caught on it fairly quickly, the Americans didn't believe it until June 1942, when the Germans spoke about it on the radio, allowing ULTRA to prove it and force the US to change codes (and recall that talkative consul).
* So the West couldn't do this, the Soviets used something called "one-time pads", where the coding method for each message was different. However, when one set got accidentally used twice, the West were able to figure out the messages and from 1946 break a good many of them. It was key to identifying a good number of Soviet moles, including the Rosenbergs and Julius Fuchs. Some people weren't prosecuted as VENONA (as it was called) was too valuable to be used in court- it was not declassified until 1995.
** The one-time pad is, as long as the key is not compromised or re-used, ''completely uncrackable''. A communications device was invented by the Norwegians after WWII based on this principle, but since each message requires pre-delivery of a key as long as the message itself, they deemed it [[AwesomeButImpractical completely useless]]. The machine was later picked up by US Intelligence, who used it as the basis of the HotLine, since books with thousands of key codes could easily be exchanged by the embassies.

[[folder:Comic Book]]

[[folder:Film]]

* ''Literature/FromRussiaWithLove'', Literature/JamesBond must collect a Soviet defector from Turkey, who is bringing a cipher machine with her. He has to start a fire in the embassy to cover up the theft.
* In the Robert Harris novel ''Enigma'', Bletchley Park has been locked out of "Shark", the German U-boat code. Part of the novel involves them getting back in, the other part making sure that the whole thing isn't blown to the Germans.
** In the later part of the story, the heroes use an Enigma machine to decrypt a message that was stolen- [[spoiler: it is a report on the Germans finding the site of the Katyn Massacre, where 20,000 Polish soldiers were murdered in 1940 by the Soviets]].
* In ''Literature/TheThirdWorldWar'', the US had cracked the Atrophos cipher being used by Cuba. In the early stages of the war, the Cubans send a long message stating that they cannot attack the US directly, but they might be able to do some small sabotage operations. While the Soviet cipher clerk is manually decrypting the message and wishing that the long-winded platitudes that begin it are done with, the Americans have broken the whole message. The Soviets interpret the message correctly (You cowards! You're wimping out like Italy in 1939), the Americans don't (They're going to attack us!) and launch air strikes on Cuba. It takes the rest of Latin America to stop a full-scale invasion.
* In ''Literature/TheThrawnTrilogy'', eventually the New Republic did figure out that Thrawn was aware of all the plans they made in the Imperial Palace on Coruscant. They spent a lot of effort trying to figure out who the spy is. Only after a slicer cracks Delta Source's transmission encryption on his own time for fun do they figure out that it was a sophisticated listening system HiddenInPlainSight.

* Most of Literature/{{Cryptonomicon}} (the 1940s bits, at least) is based around this. As with the real life section below, the Allies go to incredible amounts of effort to engineer plausible explanations for them having the information gained from intercepting enemy signals.
* Stephen Maturin of the ''Literature/AubreyMaturin'' series does this frequently. He even carefully edits the messages before passing them along to spread misinformation in enemy lines. While his friend Jack Aubrey found the operation very dishonorable, Stephen once mentioned that he has no qualms about violating an entire mail coach if it wins them the war.

* Something [[Literature/TheWheelOfTime Egwene and the other rebel Aes Sedai]] try to do while Dreaming with regards to Elaida's mail.
* In Creator/VernorVinge's novella "Literature/TrueNames", Erythrina knows the True Name of one of The Mailman's associates, which gives her enough information to tap and decrypt communications between the two.
* The Creator/ConnieWillis novel ''To Say Nothing of the Dog'' revolves around the attempt by two British timetravellers to prevent the possible exposure of the ULTRA program (see Real Life below) due to [[GodwinsLawOfTimeTravel accidental alteration of the events of the bombing of Coventry by timetravellers]].
* The W.E.B. Griffin ''Corps'' novels spend a lot of time discussing MAGIC (The codename for intercepted and decrypted Japanese communications), the importance of the data brought in by it, and the efforts necessary to ensure that (As one non-MAGIC communication obliquely put it) the rabbit stayed in the hat.
* ''Literature/TheAIGang'': In ''Robot Trouble'', Ramone Korbuscek infiltrates the island disguised as a security guard, and after a while starts reading security chief Brody's mail, among other things intercepting and destroying a letter advising Brody to investigate the guard Korbuscek is disguised as.

* ''Literature/TwentyYearsAfter'': Athos, being a perfect OfficerAndAGentleman, is horrified at the idea of reading letters carried by captured messengers. Aramis, being far more pragmatic, is proven right after those letters prove instrumental to freeing d'Artagnan and Porthos.

[[folder:Live Action TV]]

* ''Series/ChariteAtWar'': Professor Jung, a French medic who's conscripted to serve in a Berlin hospital in UsefulNotes/NaziGermany, is not happy that his letters to and from home are controlled by censorship. It's not just enemy's mail, though -- Otto is a German soldier, but he has to be careful with what he writes, too.
* ''Series/BlakesSeven''. Episodes like "Seek-Locate-Destroy" and "Killer" involved the theft of a component that would allow Blake to crack Federation codes, no doubt inspired by the revelation just a few years previously about the war-winning importance of ULTRA (see Real Life). Later the rebels would get hold of a MagicalComputer called Orac who could do this as a matter of course.

* The [[http://en.wikipedia.org/wiki/Zimmermann_Telegram Zimmermann Telegram]] was a diplomatic note that was sent by the German Empire to Mexico, looking at seeing whether Mexico would be interested in declaring war on the United States should the increasingly pro-Triple-Entente US enter World War I. The Germans promised financial and military aid to help [[MexicoCalledTheyWantTexasBack Mexico reclaim the "lost territories" of Arizona, New Mexico, and Texas]]. This telegram was intercepted by the British as it was passing through the US (direct communication lines from Germany to the Western Hemisphere were cut by the British, so the only way the Germans could communicate with their embassies in the Americas was via Canada and the US) and turned over to the Americans (Britain had to find other pieces of evidence so as to avoid admitting it was reading the US's diplomatic mail), thus further enraging American public opinion and leading to the US's entry into UsefulNotes/WW1 on the side of the Entente. (Mexico, by the way, declined the offer.)

* The Tsar's SecretPolice the ''okhranka'' had their own "black cabinet" where operatives steamed open envelopes and cracked revolutionary codes (some of their techniques would be passed onto the Soviet secret police). As they also put surveillance on the regular police, some police chiefs took to writing letters containing flattering comments about their bosses in the hope of it leaking back to them via the ''okhranka''. When Pyotr Durnovo became interior minister in late 1905, he found a copy of an intercepted letter he had written [[RussianReversal instructing that his own mail should not be read]].

* One plot point in ''Film/ToraToraTora'' is that the US Military can decrypt the Japanese diplomatic codes. However, it is time-consuming, and very very secret. So secret, that at one point the President of the United States is removed from the list of people authorized to read the decoded messages because someone in his office improperly disposed of a decoded message. This of course only serves to add to the [[PoorCommunicationKills information delay]] that contributes to the Americans' failure to prepare for the impending attack.

* During the English Civil War, John Thurloe became the Spymaster for the Commonwealth, and later the Protectorate. He also became Postmaster-General, which probably made his job quite a bit easier (It is worth mentioning that he did such a good job with governance that he was not even imprisoned after the [[RightfulKingReturns Restoration]] in exchange for assisting with central government).

* During the English Civil War, John Thurloe became the Spymaster for the Commonwealth, and later the Protectorate. He also became Postmaster-General, which probably made his job quite a bit easier (It is worth mentioning that he did such a good job with governance that he was not even imprisoned after the [[RightfulKingReturns Restoration]] in exchange for assisting with central government.

** OlderThanTheyThink: in the [[UsefulNotes/WorldWarI previous war]], Italian communications were handled in [[http://en.wikipedia.org/wiki/Sardinian_language Sardinian Language]] (''Sardu''): regarded by many scholars to be the living language closest to Classical Latin, it is not an Italian dialect nor by any means related to Italian. In Italy, it is notoriously known for its difficulty to be actually understood by anyone not speaking it (that is, Italians and many Sardinians themselves, being and endangered language), unless spoken ''very'' slowly. And to be sure it couldn't be understood, the code-talkers weren't Italians speaking the literary version of Sardinian (that ''may'' have been understood), but actual Sardinians speaking their native dialects (which, even though they are all pretty much mutually intelligible, vary greatly the pronunciation of words).