Non-trivial Black-Box Combiners for Collision-Resistant Hash-Functions Don't Exist

A (k, )-robust combiner for collision-resistant hash-functions is a construction which from hash-functions constructs a hash-function which is collision-resistant if at least k of the components are collisionresistant. One trivially gets a (k, )-robust combiner by concatenating the output of any − k + 1 of the components, unfortunately this is not very practical as the length of the output of the combiner is quite large. We show that this is unavoidable as no black-box (k, )-robust combiner whose output is significantly shorter than what can be achieved by concatenation exists. This answers a question of Boneh and Boyen (Crypto’06).

• Type: Conference
• Year: 2007
• Where: EUROCRYPT
• Authors: Krzysztof Pietrzak
• Keywords: )-robust Combiner, Collision-resistant Hash-functions, Concatenation Exists, Cryptography, EUROCRYPT 2007