Shannon security

The first important step towards modem scientific cryptology was Claude Shannon s work [Shan49]. There, for the first time, a precise (and, according to informal requirements, certainly sufficient) notion of security for any type of cryptologic scheme was defined the information-theoretic security of secrecy schemes, sometimes called Shannon security. Roughly, the definition requires that a ciphertext provides an outsider with no additional information at all about the message. The information-theoretic notion means that the scheme is absolutely unbreakable, i.e., unbreakable even by attackers with unrestricted computing power and unrestricted memory. 

A similar work for authentication schemes was only published 15 years later In [GiMS74], the information-theoretic, i.e., absolute security of symmetric authentication schemes was defined. Schemes complying with this definition are often called authentication codes. Like Claude Shannon s work, [GiMS74] already contains both concrete constructions of authentication codes and lower bounds on the achievable efficiency, and in particular, the key length. In contrast to secrecy schemes, however, the upper and lower bounds are not identical furthermore, the constructions are less trivial. Therefore, there has been further research in this field. 

Coauthor Shannon designed a system considering all the normal deficiencies and with a 20% security factor, but he found that the system was just large enough to control the flue gas temperatiue entering the recuperator. This emphasizes the need to play it safe with expensive long-term equipment design and selection. 

Two important properties that can be used to help in guiding the design of a secure cryptosystem, identified by Claude Shannon in 1949, are confusion and diffusion. Confusion measures the complexity of the relationship between the key and the ciphertext. Diffusion measures the degree to which small changes in the plaintext have large changes in the ciphertext. 

I thank my wife (Amber), children (Kylee, Jackson, Nathan, Tyler, Shannon), parents (Carole, Bob), and family (Anne, Bette, Dana, Dixie, Kara, Leah, Stan) for their love and support. My work on this book was supported by cooperative agreement U93MC00174 from the Office of Adolescent Health, Maternal and Child Health Bureau (Title V, Social Security Act), Health Resources and Services Administration, with co-funding by the Center for Mental Health Services, Substance Abuse and Mental Health Services Administration. (PHS413) MDW... 

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