35017
Another notable paper published in 1949 is " Communication Theory of Secrecy Systems " , a declassified version of his wartime work on the mathematical theory of cryptography , in which he proved that all theoretically unbreakable ciphers must have the same requirements as the one-time pad .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
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