Science in China Series F

, Volume 49, Issue 3, pp 286–301 | Cite as

Security analysis of a new stream cipher



In this paper, we analyze the security of a new stream cipher-COSvd(2, 128). This cipher was proposed by E. Filiol et al. at the ECRYPT SASC’2004 (The State of the Art of Stream Ciphers). It uses clock-controlled non-linear feedback registers together with an S-box controlled by a chaotic sequence and was claimed to prevent any existing attacks. However, our analysis shows that there are some serious security flaws in the design of the S-box, resulting in heavy biased byte distribution in the keystream. In some broadcast applications, this flaw will cause a ciphertext-only attack with high success rate. Besides, there are also many security flaws in other parts of the cipher. We point out these flaws one by one and develop a divide-and-conquer attack to recover the secret keys from O(226)-byte known plaintext with success rate 93.4597% and complexity O(2113), which is much lower than 2512, the complexity of exhaustive search.


stream cipher divide-and-conquer attack non-linear feedback shift registers (NLFSR) chaotic sequence 


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Copyright information

© Science in China Press 2006

Authors and Affiliations

  1. 1.State Key Laboratory of Information Security, Institute of SoftwareChinese Academy of SciencesBeijingChina

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