Cryptology ePrint Archive: Report 2008/128

A Chosen IV Attack Using Phase Shifting Equivalent Keys against DECIM v2

Hidehiko Nakagami and Ryoichi Teramura and Toshihiro Ohigashi and Hidenori Kuwakado and Masakatu Morii

Abstract: DECIM v2 is a stream cipher submitted to the ECRYPT stream cipher project (eSTREAM) and ISO/IEC 18033-4. No attack against DECIM v2 has been proposed yet. In this paper, we propose a chosen IV attack against DECIM v2 using a new equivalent key class. Our attack can recover an $80$-bit key with a time complexity of $2^{79.90}$ when all bits of the IV are zero. This result is the best one on DECIM v2.

Category / Keywords: secret-key cryptography / cryptanalysis, equivalent keys, stream cipher, DECIM v2, eSTREAM

Date: received 21 Mar 2008, last revised 16 Apr 2008

Contact author: mmorii at kobe-u ac jp

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Version: 20080416:075208 (All versions of this report)

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