Paper 2010/160

A Flaw in The Internal State Recovery Attack on ALPHA-MAC

Shengbao Wu and Mingsheng Wang and Zheng Yuan

Abstract

An distinguisher was constructed by utilizing a 2-round collision differential path of ALPHA-MAC, with about $2^{65.5}$ chosen messages and $2^{65.5}$ queries. Then, this distinguisher was used to recover the internal state(\cite{Yuan1},\cite{Yuan2}). However, a flaw is found in the internal state recovery attack. The complexity of recovering the internal state is up to $2^{81}$ exhaustive search. And the complexity of the whole attack will be up to $2^{67}$ chosen messages and $2^{81}$ exhaustive search. To repair the flaw, a modified 2-round differential path of ALPHA-MAC is present and a new distinguisher based on this path is proposed. Finally, an attack with about $2^{65.5}$ chosen messages and $2^{65.5}$ queries is obtained under the new distinguisher.