Cryptanalysis of WG-7: a lightweight stream cipher

Authors:
Mohammad Ali Orumiehchiha;Josef Pieprzyk;Ron Steinfeld
Affiliations:
Center for Advanced Computing --- Algorithms and Cryptography, Department of Computing, Faculty of Science, Macquarie University, Sydney, Australia NSW 2109;Center for Advanced Computing --- Algorithms and Cryptography, Department of Computing, Faculty of Science, Macquarie University, Sydney, Australia NSW 2109;Clayton School of Information Technology, Monash University, Clayton, Australia VIC 3800
Venue:
Cryptography and Communications
Year:
2012

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Abstract

WG-7 is a stream cipher based on WG stream cipher and has been designed by Luo et al. (2010). This cipher is designed for low cost and lightweight applications (RFID tags and mobile phones, for instance). This paper addresses cryptographic weaknesses of WG-7 stream cipher. We show that the key stream generated by WG-7 can be distinguished from a random sequence after knowing 213.5 keystream bits and with a negligible error probability. Also, we investigate the security of WG-7 against algebraic attacks. An algebraic key recovery attack on this cipher is proposed. The attack allows to recover both the internal state and the secret key with the time complexity about 227.