[Resource Topic] 2006/049: Crossword Puzzle Attack on NLS

Welcome to the resource topic for 2006/049

Title:
Crossword Puzzle Attack on NLS

Authors: Joo Yeon Cho, Josef Pieprzyk

Abstract:

NLS is one of the stream ciphers submitted to the eSTREAM project.
We present a distinguishing attack on NLS by Crossword Puzzle (CP) attack method
which is newly introduced in this paper.
We build the distinguisher by using linear approximations of
both the non-linear feedback shift register (NFSR) and the nonlinear filter function (NLF).
Since the bias of the distinguisher depends on the Konst value,
which is a key-dependent word,
we present the graph showing how the bias of distinguisher vary with Konst.
In result, we estimate the average bias to be around O(2^{-30}).
Therefore, we claim that NLS is distinguishable from truly random cipher after observing
O(2^{60}) keystream words on the average.
The experiments also show that our distinguishing attack is successful on 90.3\% of Konst
among 2^{32} possible values.

ePrint: https://eprint.iacr.org/2006/049

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