关键词: 密码学, 广义自缩生成器, 区分攻击, 线性反馈移位寄存器, 多项式

Abstract:

With simple construction and easy implementation, the generalized self-shrinking generator is a keystream generator intended to be used as a stream cipher. This paper investigates the security of the generalized self-shrinking generator. We propose two distinguishing attacks on the generalized self-shrinking sequences by using the feedback polynomial and the sequence v. The results show that the attacker can launch a distinguishing attack by choosing the h^w-1 keystream bit of the generalized self-shrinking generator, if the feedback polynomial f(x) is of hamming weight w and degree h. On the other hand, if the hamming weight of f(x) is low, then the attacker can launch a distinguishing attack, and the attack complexity depends on the weight of f(x).  Therefore, neither type of the polynomials can be chosen as the feedback polynomials of the generalized self-shrinking generator. Users should choose the feedback polynomial carefully, otherwise the stream cipher can suffer from distinguishing attacks.

Key words: cryptography, generalized self-shrinking generators, distinguishing attacks, linear feedback shift registers, polynomials