IACR News item: 12 December 2015
Zhiqiang Lin, Dingyi Pei, Dongdai Lin
ePrint Report
Stream ciphers based on Linear Feedback Shift Registers (LFSRs) have faced algebraic attacks. To avoid this
kind of attacks, Feedback with Carry Shift Registers (FCSRs) have been proposed as an alternative. In order to eliminate a so-called LFSRization weakness, FCSRs have been implemented using ring representation instead of the Galois one. A ring FCSR is determined by its transition matrix $A$. Its connection integer, which is related to the properties of the output sequences,
is $q=\mbox{det}(I-2A)$.
In this paper, we show how to calculate the determinant $\mbox{det}(I-2A)$ of transition matrices with a critical path of length 1 and fan-out 2. Moreover, we propose algorithms to construct such transition matrices (binary case) based on searching target connection integers.
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