Paper 2009/034

On a Conditional Collision Attack on NaSHA-512

S. Markovski, A. Mileva, V. Dimitrova, and D. Gligoroski

Abstract

A collision attack on NaSHA-512 was proposed by L. Ji et al. The claimed complexity of the attack is $2^{192}$. The proposed attack is realized by using a suitable differential pattern. In this note we show that the correct result that can be inferred from their differential pattern is in fact a conditional one. It can be stated correctly as follows: A collision attack on NaSHA-512 of complexity $k=1,2,\dots,2^{320}$ can be performed with an unknown probability of success $p_k$, where $ 0\le p_1\le p_2\le p_{2^{320}}\le 1$. Consequently, the attack proposed by L. Ji et al. can be considered only as a direction how a possible collision attack on NaSHA-512 could be realized. The birthday attack remains the best possible attack on NaSHA-512.