Toshiaki Tanaka

Hash functions using stream ciphers as components perform fast on a variety of platforms. However, stream-cipher-based hash functions (SCHs) have not been studied sufficiently yet. In this paper, we present a model of SCHs consisting of two parts: a pre-computation phase and a stream cipher phase. We apply this model to existing broken SCHs, Abacus and Boole, and analyze the vulnerabilities corresponding to existing attacks for each part of our model. By applying our model to these algorithms, weak parts in the algorithms are revealed, and we show that these vulnerabilities can be removed by minor modifications to each part. Furthermore, we clarify the requirements for the pre-computation phase and the stream cipher phase to realize secure SCHs.