改进的多步法快速相关攻击及其应用

Improved multi-pass fast correlation attacks with applications

本文提出了两个新的流密码多步法快速相关攻击算法.第一个算法适用于噪音不是很大,而攻击者只有很少预计算资源的环境.第二个算法适用于高噪音而只能获得有限密钥流的场合.新算法均适用于任何形式的LFSR,并在所考虑情况下优于以前的结果.作为应用,本文分别给出一级蓝牙流密码E0和LILI-128新的密钥恢复攻击.给定237比特密钥流和228字节存储空间,针对一级蓝牙流密码E0的新攻击可以在235.1次操作中完成.给定224比特密钥流和224.5字节存储,针对LILI-128的新攻击复杂度为270.6次操作.

In this paper we propose two new algorithms for multi-pass fast correlation attacks on stream ciphers.The first algorithm aims at fast symbol-wise decoding in the circumstances that the noise is not very high and we have little resource for pre-computation.The second algorithm deals with the practical decoding problem in the high noise and limited keystream cases.The new algorithms are applicable to arbitrary form LFSR and compare favorably to the previously known algorithms in the scenarios under consideration.As applications,we demonstrate new key recovery attacks on one-level Bluetooth E0 and LILI-128,respectively.Given 2 37-bit keystream and 2 28-byte memory,our attack against one-level E0 needs 2 35.1 operations.Given 2 24-bit keystream and 2 24.5-byte memory,our attack on LILI-128 has time complexity 2 70.6 operations.