Bias in the nonlinear filter generator output sequence
Nonlinear filter generators are common components used in the keystream generators for stream ciphers and more recently for authentication mechanisms. They consist of a Linear Feedback Shift Register (LFSR) and a nonlinear Boolean function to mask the linearity of the LFSR output. Properties of the output of a nonlinear filter are not well studied. Anderson noted that the m-tuple output of a nonlinear filter with consecutive taps to the filter function is unevenly distributed. Current designs use taps which are not consecutive. We examine m-tuple outputs from nonlinear filter generators constructed using various LFSRs and Boolean functions for both consecutive and uneven (full positive difference sets where possible) tap positions. The investigation reveals that in both cases, the m-tuple output is not uniform. However, consecutive tap positions result in a more biased distribution than uneven tap positions, with some m-tuples not occurring at all. These biased distributions indicate a potential flaw that could be exploited for cryptanalysis
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|Item Type:||Journal Article|
|Keywords:||Stream Cipher, Nonlinear filter generators, Linear Feedback Shift Registers|
|Subjects:||Australian and New Zealand Standard Research Classification > INFORMATION AND COMPUTING SCIENCES (080000) > COMPUTER SOFTWARE (080300) > Computer System Security (080303)|
|Divisions:||Past > QUT Faculties & Divisions > Faculty of Science and Technology|
Past > Institutes > Information Security Institute
|Copyright Owner:||Copyright 2010 Malaysian Society for Cryptology Research|
|Deposited On:||26 Nov 2010 08:43|
|Last Modified:||30 Nov 2010 13:30|
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