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The Role of Information Theory in Cryptography

Ueli Maurer

This paper reviews the relations between information theory and cryptography, from Shannon's foundation of information theory to the most recent developments in unconditionally-secure key-agreement protocols. For a long time, information theory has mainly been used in cryptography to prove lower bounds on the size of the secret key required to achieve a certain level of security in secrecy and authentication systems. More recent results on a slightly extended model suggest that perfect secrecy is practically possible with only a short secret key, thus apparently contradicting Shannon's lower bound on the key size of a perfect cipher.