We analyse asymptotically performances and convergence of fast iterative correlation attacks for the cryptanalysis of stream ciphers using linear feedback shift registers as autonomous stages. Finally, we describe and analyse an improvement for this class of cryptanalytical algorithms.

We consider the problem of estimating the feedback coefficients of a linear feedback shift register (LFSR) based on noisy observations. In the current approach, the coefficients are endowed with a probabilistic model. Gradient ascent updates to coefficient probabilities are computable using recursions developed by means of the EM algorithm. Reduced-complexity approximations are also developed b...

Binary sequences are the most fundamental random numbers and have been extensively used in several applications such as spread-spectrum CDMA communications and cryptosystems. M-sequences, Kasami sequences, and Gold sequences, all of which can be generated by linear feedback shift registers (LFSRs), are well known as conventional binary sequences [1]. It is also well known that chaos phenomena c...

The shrinking generator is a well-known keystream generator composed of two linear feedback shift registers, LFSR1 and LFSR2, where LFSR1 is clock-controlled according to regularly clocked LFSR2. A probabilistic analysis of the shrinking generator which shows that this generator can be vulnerable to a specific fast correlation attack is conducted. The first stage of the attack is based on a rec...

We propose a novel system for optical encryption based on an optical XOR and optical Linear Feedback Shift Register (oLFSRs). Though we choose LFSR for its ability to process optical signals at line rate, we consider the fact that it offers no cryptographic security. To address the security shortfall, we propose implementation of parallel oLFSRs, whereby the resulting key-stream at line rate is...

Two forms of nonlinear-feedback shift-registers are considered. In the Type-I register, the feedback output is added to the shift-register contents at an arbitrary number of stages. In the type-11 register, the feedback is input to the first stage only. It is shown that for every Type-I register there is an equivalent Type-II register in the sense that the autonomous state diagrams differ only ...

In this paper we show that an accumulator can be modified to behave as a Non-Linear Feedback Shft Register suitable for test response compaction. The hardware required for this modification is less than that required to mod& a register to a Multiple Input Linear Feedback Shgt Register, MISR. We show with experiments on ISCAS’85, ISCAS’89 benchmark circuits and various types of multipliers that ...

In their paper, G.Gong and S.Q.Jiang construct a new pseudorandom sequence generator by using two ternary linear feedback shift registers (LFSR). The new generator is called an editing generator which a combined model of the clock-controlled generator and the shrinking generator. For a special case (Both the base sequence and the control sequence are mm-sequence of degree n), the period, linear...

It is well known that in order to build linear scramblers and stream ciphers that are robust against correlation-based reconstruction, primitive polynomials which do not have sparse multiples of moderate degrees must be used. In this paper, the existence and density of such ‘good primitive polynomials’ are studied. Two theoretical lower bounds on the degree d of the primitive polynomial are der...

Most stream ciphers based on linear feedback shift registers (LFSR) are vulnerable to recent algebraic attacks. In this survey paper, we describe generic attacks: existence of algebraic equations and fast algebraic attacks. The generic attacks only states the existence and gives the upper bound of the complexity. Thus we should find good algebraic equations, case by case, in order to apply the ...