Cryptanalysis of the stream cipher BEAN

Authors:
Martin Ågren;Martin Hell
Affiliations:
Lund University, Lund, Sweden;Lund University, Lund, Sweden
Venue:
Proceedings of the 4th international conference on Security of information and networks
Year:
2011

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Abstract

BEAN is a recent stream cipher proposal that uses Feedback with Carry Shift Registers (FCSRs) and an output function. There is a sound motivation behind the use of FCSRs in BEAN as they provide several cryptographically interesting properties. In this paper, we show that the output function is not optimal. We give an efficient distinguisher and a key recovery attack that is slightly better than brute force, requiring no significant memory. We then show how this attack can be made better with access to more keystream. Already with access to 6 KiB, the 80-bit key is recovered in time 273.