• Journal of the Korea Institute of Information Security & Cryptology
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• v.17 no.3
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• pp.109-116
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• 2007

In this paper, we analyse the security of the variant of Self-Shrinking generator proposed by Chang et al. against a guess-and-determine attack. This variant, which we call SSG-XOR is claimed to have better cryptographic properties than the Self-Shrinking generator in a practical setting. But we show that SSG-XOR is weaker than the Self-Shrinking generator from the viewpoint of guess-and-determine attack.

• Journal of Information Processing Systems
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• v.7 no.1
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• pp.151-158
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• 2011

Bivium is a simplified version of Trivium, a hardware profile finalist of the eSTREAM project. Bivium has an internal state size of 177 bits and a key length of 80 bits. In this paper, a guess and determine attack on this cipher is introduced. In the proposed method, the best linear approximations for the updating functions are first defined. Then by using these calculated approximations, a system of linear equations is built. By guessing 30 bits of internal state, the system is solved and all the other 147 remaining bits are determined. The complexity of the attack is O ($2^{30}$), which is an improvement to the previous guess and determine attack with a complexity of order O($2^{52.3}$).