Cryptology ePrint Archive: Report 2005/164

A Distinguish attack on COSvd Ciphers

Mohammad Ali Orumiehchi ha and Dr.R. Mirghadri

Abstract: Abstract: The COSvd Ciphers has been proposed by Filiol and others (2004). It is a strengthened version of COS stream cipher family denoted COSvd that has been adopted for at least one commercial standard. We propose a distinguish attack on this version, and prove that, it is distinguishable from a random stream. In the COSvd Cipher used one S-Box (10◊8) on the final part of cipher. We focus on S-Box and use weakness this S-Box for distinguish attack. In addition, found a leak on HNLL that the sub s-boxes donít select uniformly. We use this property for an Improve distinguish attack.

Category / Keywords: secret-key cryptography / Stream cipher, COSvd cipher, Distinguish attack, nonlinear feedback shift registers, chaotic layer.

Date: received 16 May 2005

Contact author: maorum at yahoo com

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Version: 20050606:200839 (All versions of this report)

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