The stream ciphers Py, Pypy and Py6 were designed by Biham and Seberry for the ECRYPT-eSTREAM project in 2005. The ciphers were promoted to the ‘Focus’ ciphers of the Phase II of the eSTREAM project. However, due to some cryptanalytic results on the ciphers, strengthened versions of the ciphers, namely TPy, TPypy and TPy6 were built. So far there exists no attacks on TPy6. In this paper, we fin...

In this paper, we examine a recently proposed mode of operation for block ciphers which we refer to as statistical cipher feedback (SCFB) mode. SCFB mode configures the block cipher as a keystream generator for use in a stream cipher such that it has the property of statistical self-synchronization, thereby allowing the stream cipher to recover from slips in the communications channel. Statisti...

Algebraic attacks on LFSR-based stream ciphers recover the secret key by solving an overdefined system of multivariate algebraic equations. They exploit multivariate relations involving key bits and output bits and become very efficient if such relations of low degrees may be found. Low degree relations have been shown to exist for several well known constructions of stream ciphers immune to al...

A wide family of nonlinear sequence generators, the so-called clockcontrolled shrinking generators, has been analyzed and identified with a subset of linear cellular automata. The algorithm that converts the given generator into a linear model based on automata is very simple and can be applied in a range of practical interest. Due to the linearity of these automata as well as the characteristi...

In this paper, we present the rainbow attack on stream ciphers filtered by Maiorana-McFarland functions. This can be considered as a generalization of the time-memory-data trade-off attack of Mihaljevic and Imai on Toyocrypt. First, we substitute the filter function in Toyocrypt (which has the same size as the LFSR) with a general MaioranaMcFarland function. This allows us to apply the attack t...

In this paper, we present the time-memory-data (TMD) trade-off attack on stream ciphers filter function generators and filter cominers based on Maiorana-McFarland functions. This can be considered as a generalization of the time-memory-data trade-off attack of Mihaljevic and Imai on Toyocrypt. First, we substitute the filter function in Toyocrypt (which has the same size as the LFSR) with a gen...

In this paper we investigate nonlinear equivalence of stream ciphers over a finite field, exemplified by the pure LFSR-based filter generator over F2. We define a nonlinear equivalence class consisting of filter generators of length n that generate a binary keystream of period dividing 2−1, and investigate certain cryptographic properties of the ciphers in this class. We show that a number of i...

This paper presents a new attack called Decimation Attack of most stream ciphers. It exploits the property that multiple clocking (or equivalently d-th decimation) of a LFSR can simulate the behavior of many other LFSRs of possible shorter length. It yields then signiicant improvements of all the previous known correlation and fast correlation attacks. A new criterion on the length of the polyn...

T he aim of this dissertation is to show some cryptanalytical results on a selection of stream ciphers. We have grouped theory and results into three main parts. The first part focuses on the FCSR-based constructions X-FCSR and F-FCSRH v3. For the X-FCSR family of stream ciphers we perform a severe state recovery attack. This attack works for both X-FCSR-128 and X-FCSR-256. We then develop a ge...

SNOW 2.0 is a word oriented stream cipher that has been selected as a standard stream cipher on ISO/IEC 18033-4. One of the general attacks on the stream ciphers is Guess and Determine attack. Heuristic GD attack is GD attack that represents an algorithmic method to analysis the stream cipher with the variables of the same size. The results of HGD attack on TIPSY, SNOW 1.0 and SNOW 2.0 stream c...