Paper 2010/482

On Instantiation of the Random Oracle

He Ge

Abstract

In the current methodology of the Random Oracle Model, the random oracle is instantiated by a ``good cryptographic hash function''. However, due to the work of Canetti, Goldreich and Halevi, such methodology has been found problematic because there exist a construction secure in the Random Oracle Model, but any instantiation of the random oracle by any fully specified function which includes also any ``good cryptographic hash function'' will result in an insecure implementation. We investigate the Canetti-Goldreich-Halevi method, and propose a new method for the instantiation of the random oracle, in which the random oracle is instantiated by a floating pseudorandom function. Under this new method, Canetti, Goldreich and Halevi's construction will have a secure implementation. Our work puts the methodology of the Random Oracle Model on firm grounds.