In this paper we study two possible approaches to improving existing schemes for constructing hash functions that hash arbitrary long messages. First, we introduce a continuum of function classes that lie between universal one-way hash functions and collision-resistant functions. For some of these classes efficient (yielding short keys) composite schemes exist. Second, we prove that the schedule of the Shoup construction, which is the most efficient composition scheme for universal one-way hash functions known so far, is optimal.
Lecture Notes in Computer Science, 2045 (2001), 166-181 (Advances in Cryptology - EUROCRYPT'01