Cryptology ePrint Archive: Report 1997/007

Towards realizing random oracles: Hash functions that hide all partial information

Ran Canetti

Abstract: The random oracle model is a very convenient setting for designing cryptographic protocols. In this idealized model all parties have access to a common, public random function, called a random oracle. Protocols in this model are often very simple and efficient; also the analysis is often clearer. However, we do not have a general mechanism for transforming protocols that are secure in the random oracle model into protocols that are secure in real life. In fact, we do not even know how to meaningfully specify the properties required from such a mechanism. Instead, it is a common practice to simply replace - often without mathematical justification - the random oracle with a `cryptographic hash function' (e.g., MD5 or SHA). Consequently, the resulting protocols have no meaningful proofs of security.

Category / Keywords: Random oracles, Hash functions, Collision resistance, Semantic security

Publication Info: Appeared in the THEORY OF CRYPTOGRAPHY LIBRARY and has been included in the ePrint Archive.

Date: received June 2nd, 1997.

Contact author: canetti at watson ibm com

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