Communication Theory of Secrecy Systems

{{Short description|1949 paper by Claude Shannon}}

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| name = Communication Theory of Secrecy Systems

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| author = Claude E. Shannon

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| subject = Cryptography

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| pub_date = 1949

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"Communication Theory of Secrecy Systems" is a paper published in 1949 by Claude Shannon discussing cryptography from the viewpoint of information theory.Shannon, "Communication Theory of Secrecy Systems," p. 656. [http://www.prism.net/user/dcowley/shannon/shannon01.jpg] It is one of the foundational treatments (arguably the foundational treatment) of modern cryptography.{{Cite book |last1=Shimeall |first1=Timothy J. |url=https://books.google.com/books?id=eZBqAAAAQBAJ&pg=PA167 |title=Introduction to Information Security: A Strategic-Based Approach |last2=Spring |first2=Jonathan M. |publisher=Syngress |year=2013 |isbn=978-1597499699 |pages=167 |language=en}} His work has been described as a "turning point, and marked the closure of classical cryptography and the beginning of modern cryptography."{{Cite journal |last1=Koç |first1=Çetin Kaya |last2=Özdemir |first2=Funda |date=2023 |title=Development of Cryptography since Shannon |url=https://cetinkayakoc.net/publications.html |journal=Handbook of Formal Analysis and Verification in Cryptography|pages=1–56 |doi=10.1201/9781003090052-1 |isbn=978-1-003-09005-2 |url-access=subscription }} It has also been described as turning cryptography from an "art to a science".{{Cite book |last=Zheng |first=Zhiyong |url=https://books.google.com/books?id=dG1rEAAAQBAJ&pg=PR6 |title=Modern Cryptography Volume 1: A Classical Introduction to Informational and Mathematical Principle |date=2022 |publisher=Springer Singapore |isbn=978-981-19-0919-1 |series=Financial Mathematics and Fintech |location=Singapore |pages=vi |language=en |doi=10.1007/978-981-19-0920-7}} It is also a proof that all theoretically unbreakable ciphers must have the same requirements as the one-time pad.

The paper serves as the foundation of secret-key cryptography, including the work of Horst Feistel, the Data Encryption Standard (DES), Advanced Encryption Standard (AES), and more.{{Cite journal |last1=Koç |first1=Çetin Kaya |last2=Özdemir |first2=Funda |date=2023 |title=Development of Cryptography since Shannon |url=https://cetinkayakoc.net/docs/r14.pdf |journal=Handbook of Formal Analysis and Verification in Cryptography |pages=1–56 |doi=10.1201/9781003090052-1 |isbn=978-1-003-09005-2}} In the paper, Shannon defined unicity distance, and the principles of confusion and diffusion, which are key to a secure cipher.{{Cite book |url=https://books.google.com/books?id=1_GeBQAAQBAJ&pg=PA362 |title=Chaos Synchronization and Cryptography for Secure Communications: Applications for Encryption |date=2011 |publisher=Information Science Reference |isbn=978-1-61520-737-4 |editor-last=Banerjee |editor-first=Santo |location=Hershey, PA |pages=362 |language=en |oclc=495781438}}

Shannon published an earlier version of this research in the formerly classified report A Mathematical Theory of Cryptography, Memorandum MM 45-110-02, Sept. 1, 1945, Bell Laboratories.[https://www.iacr.org/museum/shannon/shannon45.pdf A Mathematical Theory of Cryptography][http://www.research.att.com/~njas/doc/shannonbib.html Bibliography of Claude Elwood Shannon] This report also precedes the publication of his "A Mathematical Theory of Communication", which appeared in 1948.