**State convergence and keyspace reduction of the Mixer stream cipher**

*Sui-Guan Teo and Kenneth Koon-Ho Wong and Leonie Simpson and Ed Dawson*

**Abstract: **This paper presents an analysis of the stream cipher Mixer, a bit-based cipher with structural components similar to the well-known Grain cipher and the LILI family of keystream generators. Mixer uses a 128-bit key and 64-bit IV to initialise a 217-bit internal state. The analysis is focused on the initialisation function of Mixer and shows that there exist multiple key-IV pairs which, after initialisation, produce the same initial state, and consequently will generate the same keystream. Furthermore, if the number of iterations of the state update function performed during initialisation is increased, then the number of distinct initial states that can be obtained decreases. It is also shown that there exist some distinct initial states which produce the same keystream, resulting in a further reduction of the effective key space.

**Category / Keywords: **secret-key cryptography / Stream cipher, initialisation, state convergence, Mixer, LILI, Grain

**Date: **received 9 Dec 2010

**Contact author: **sg teo at qut edu au

**Available format(s): **PDF | BibTeX Citation

**Note: **Submitted for review for the Journal of Discrete Mathematical Sciences & Cryptography

**Version: **20101213:185717 (All versions of this report)

**Short URL: **ia.cr/2010/628

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