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One-time pad
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===Exploits=== While one-time pads provide perfect secrecy if generated and used properly, small mistakes can lead to successful cryptanalysis: * In 1944–1945, the [[U.S. Army]]'s [[Signals Intelligence Service]] was able to solve a one-time pad system used by the German Foreign Office for its high-level traffic, codenamed GEE.<ref>Erskine, Ralph, "Enigma's Security: What the Germans Really Knew", in ''Action this Day'', edited by Ralph Erskine and Michael Smith, pp. 370–386, 2001.</ref> GEE was insecure because the pads were not sufficiently random—the machine used to generate the pads produced predictable output. * In 1945, the US discovered that [[Canberra]]–[[Moscow]] messages were being encrypted first using a code-book and then using a one-time pad. However, the one-time pad used was the same one used by Moscow for [[Washington, D.C.]]–Moscow messages. Combined with the fact that some of the Canberra–Moscow messages included known British government documents, this allowed some of the encrypted messages to be broken.{{citation needed|date=June 2021}} * One-time pads were employed by [[Soviet Union|Soviet]] espionage agencies for covert communications with agents and agent controllers. Analysis has shown that these pads were generated by typists using actual typewriters. This method is not truly random, as it makes the pads more likely to contain certain convenient key sequences more frequently. This proved to be generally effective because the pads were still somewhat unpredictable because the typists were not following rules, and different typists produced different patterns of pads. Without copies of the key material used, only some defect in the generation method or reuse of keys offered much hope of cryptanalysis. Beginning in the late 1940s, US and UK intelligence agencies were able to break some of the Soviet one-time pad traffic to [[Moscow]] during WWII as a result of errors made in generating and distributing the key material. One suggestion is that Moscow Centre personnel were somewhat rushed by the presence of German troops just outside Moscow in late 1941 and early 1942, and they produced more than one copy of the same key material during that period. This decades-long effort was finally codenamed [[Venona project|VENONA]] (BRIDE had been an earlier name); it produced a considerable amount of information. Even so, only a small percentage of the intercepted messages were either fully or partially decrypted (a few thousand out of several hundred thousand).<ref name=":2">{{cite news|title=The Venona Translations|url=http://www.nsa.gov/about/_files/cryptologic_heritage/publications/coldwar/venona_story.pdf|work=The Venona Story|publisher=[[National Security Agency]]|location=[[Fort Meade, Maryland]]|date=2004-01-15|page=17th (of 63 in PDF) but marked 15|access-date=2009-05-03|archive-url=https://web.archive.org/web/20090510052927/http://www.nsa.gov/about/_files/cryptologic_heritage/publications/coldwar/venona_story.pdf|archive-date=2009-05-10|quote=Arlington Hall's ability to read the VENONA messages was spotty, being a function of the underlying code, key changes, and the lack of volume. Of the message traffic from the KGB New York office to Moscow, 49 percent of the 1944 messages and 15 percent of the 1943 messages were readable, but this was true of only 1.8 percent of the 1942 messages. For the 1945 KGB Washington office to Moscow messages, only 1.5 percent were readable. About 50 percent of the 1943 GRU-Naval Washington to Moscow/Moscow to Washington messages were read but none from any other year.|url-status = dead}}</ref> * The one-time tape systems used by the U.S. employed electromechanical mixers to combine bits from the message and the one-time tape. These mixers radiated considerable electromagnetic energy that could be picked up by an adversary at some distance from the encryption equipment. This effect, first noticed by [[Bell Labs]] during World War II, could allow interception and recovery of the plaintext of messages being transmitted, a vulnerability code-named [[Tempest (codename)|Tempest]].<ref name=boaklectures1 />{{rp|pp. 89 ff}}
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