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A novel technique for cryptanalysis of the stream cipher Grain-v1 is given. In a particular setting, the algorithms proposed in this study provide recovery of an internal state of Grain-v1 with the expected time complexity of only 254 table look-up operations employing a memory of dimension ~270, assuming availability of 234 keystream sequences each of length 238 generated for different initial values, and the pre-processing time complexity of ~288. These figures appear as significantly better in comparison with the previously reported ones. The proposed approach for cryptanalysis primarily depends on the order of normality of the employed Boolean function in Grain-v1. Accordingly, in addition to the security evaluation insights of Grain-v1, the results of this study are also an evidence of the cryptographic significance of the normality criteria of Boolean functions.
Date of Publication: June 2012