FOX密码的中间相遇攻击

MEET-IN-THE-MIDDLE ATTACK ON FOX

FOX是基于Mediacrypt公司的需求而设计的系列分组密码。为进一步评估FOX密码的安全性,主要研究FOX密码抗中间相遇攻击的能力,根据其加密算法的结构,给出FOX64的3轮和4轮中间相遇区分器,以及FOX128的3轮中间相遇区分器。通过分别在以上区分器后加适当的轮数,对4到8轮的FOX64和4、5轮的FOX128进行中间相遇攻击,并给出攻击结果。结果证明了8轮FOX64/256是不安全的。同时表明,5轮FOX64/128、7轮FOX64/192、8轮FOX64/256和5轮FOX128/256均不能抵抗中间相遇攻击。

FOX is a family of block ciphers, which was designed according to the need of Mediacrypt. In this paper we mainly study the ability of FOX cipher in resisting the meet-in-the-middle attack in order to further evalu^tte its security. Based on the structure of FOX, 3- round and 4-round meet-in-the-middle distinguishers of FOX64 are given. 3-round meet-in-the-middle distinguishers of FOX128 are given as well. By adding proper rounds to the above distinguishers, the meet-in-the-middle attacks are applied to 4 to 8-round FOX64, and to 4 and 5- round FOX128, and the attacking results are presented. These results prove that 8-round FOX64/256 is insecure. Meanwhile, it is demon- strated that 5-round FOX64/128, 7-round FOX64/192, 8-round FOX64/256 and 5-round FOX128/256 are all not immune to meet-in-the- middle attack.