From indifferentiability to constructive cryptography (and back)

Abstract

The concept of indifferentiability of systems, a generalized form of indistinguishability, was proposed in 2004 to provide a simplified and generalized explanation of impossibility results like the noninstantiability of random oracles by hash functions due to Canetti, Goldreich, and Halevi (STOC 1998). But indifferentiability is actually a constructive notion, leading to possibility results. For example, Coron et al. (Crypto 2005) argued that the soundness of the construction C(f) of a hash function from a compression function f can be demonstrated by proving that C(R) is indifferentiable from a random oracle if R is an ideal random compression function. The purpose of this short paper is to describe how the indifferentiability notion was a precursor to the theory of constructive cryptography and thereby to provide a simplified and generalized treatment of indifferentiability as a special type of constructive statement.