A Framework for Iterative Hash Functions — HAIFA ?

Abstract. Since the seminal works of Merkle and Damg˚ard on the iteration of compression functions, hash functions were built from compression functions using the Merkle-Damg˚ard construction. Recently, several flaws in this construction were identified, allowing for second pre-image attacks and chosen target pre-image attacks on such hash functions even when the underlying compression functions are secure. In this paper we propose the HAsh Iterative FrAmework (HAIFA). Our framework can fix many of the flaws while supporting several additional properties such as defining families of hash functions and supporting variable hash size. HAIFA allows for an online computation of the hash function in one pass with a fixed amount of memory independently of the size of the message. Besides our proposal, the recent attacks initiated research on the way compression functions are to be iterated. We show that most recent proposals such as randomized hashing, the enveloped Merkle-Damg˚ard, and the RMC and ROX modes can be all be instantiated as part of the HAsh