A note on the improvement of a fast correlation attack on stream ciphers

We introduce two new correlation attacks on stream ciphers that make use of non-linearly combined linear feedback shift-registers (LFSRs). The first attack utilises the well-known Lempel-Ziv complexity measure for binary sequences. The second attack is based on the binary derivative, applied in conjunction with the distribution of runs in a binary sequence. Both attacks make use of ciphertext only, and give very good results. They are able to recover the unknown (secret) initial state of an internal LFSR, even when only a very small correlation of q=0.52 occurs between the observed ciphertext and the output of an internal LFSR, and approximately 60000 ciphertext bits are required for attacks to succeed. The computational complexity and memory requirements of the binary derivative attack are substantially lower than for the Lempel-Ziv attack, making It feasible to attack stream ciphers with LFSR-lengths of approximately 40 to 50 bits.

Linearization of nonlinear filter generators and its application to cryptanalysis of stream ciphers

Pseudonoise sequences generated by linear feedback shift registers [1] with some nonlinear combining function have been proposed [2]–[5] for cryptographic applications as running key generators in stream ciphers. In this correspondence it will be shown that the number of trials to break these ciphers can be significantly reduced by using correlation methods. By comparison of computer simulations and theoretical results based on a statistical model, the validity of this analysis is demonstrated. Rubin [6] has shown that it is computationally feasible to solve a cipher proposed by Pless [2] in a known plaintext attack, using as few as 15 characters. Here, the number of ciphertext symbols is determined to perform a ciphertext-only attack on the Pless cipher using the correlation attack. Our conclusion from the analysis is that the pseudonoise generator's output sequence and the sequences generated by the linear feedback shift registers should be uncorrelated. This leads to constraints for the nonlinear combining function to be used.

Communication security that depends on chaos can be considered as a new approach which provides protection and security of communications and maintains confidentiality because Chaos theory can be implemented in cryptosystem successfully. A stream cipher, on the other hand, is a type of symmetric cryptosystem in which the plaintext is divided into small entities known as characters. The key in stream cipher is typically generated by a random bit generator. Many key stream generators employ linear feedback shift registers (LFSRs). LFSR systems are made up of a group of LFSR units and a combining function (CF) unit. The plaintext is encrypted one bit at a time. The key is fed into a random bit generator, which produces a long series of binary signals. This "key-stream" k is then combined with plaintext m, typically via a bit-wise XOR (Exclusive-OR modulo 2 addition), to produce the ciphertext stream, which employs the same random bit generator and seed. In this paper we will introduce a new stream cipher keygenerator which using a hybrid between chaotic and combination of Linear Feedback Shift Registers (LFSR's). The proposed generator can be used to protect different types of data files (text, image, audio and video). Many kinds of tests are applied to specifying the goodness of the proposed keygenerator. The results of testing prove the efficiency of the suggested system.

At Indocrypt’2002, a new pseudorandom generator based on linear feedback shift register (LFSR) and feedback with carry shift registers (FCSR) was proposed by Arnault. And at Indocrypt’2004, Bin Zhang et al. showed that the self-synchronizing stream cipher constructed by Arnault’s pseudorandom generator was extremely weak against a chosen ciphertext attack. In this paper, we show that the synchronizing stream cipher constructed by Arnault’s pseudorandom generator bear good immunities to the attack proposed by Bin Zhang et al., but can not resist the LFSRization attack proposed by Martin Hell and Thomas Johansson. Then we propose a modification to the synchronizing stream cipher, and show that it inherits of the nice statistical properties of the pseudorandom generator and provided a resistant to the known attacks. The new architecture still has high throughput and low implementation cost.

In this paper, new method have been investigated using evolving algorithms (EA's) to cryptanalysis one of the nonlinear stream cipher cryptosystems which depends on the Linear Feedback Shift Register (LFSR) unit by using cipher text-only attack. Genetic Algorithm (GA) and Ant Colony Optimization (ACO) which are used for attacking one of the nonlinear cryptosystems called "shrinking generator" using different lengths of cipher text and different lengths of combined LFSRs. GA and ACO proved their good performance in finding the initial values of the combined LFSRs. This work can be considered as a warning for a stream cipher designer to avoid the weak points, which may be found in the stream cipher, and may be explored by the cryptanalysts. This work can find the optimal solution for text with minimum lengths of 20 characters and 100 iteration were very enough to find the real initial values of key stream.

stream ciphers encrypt the data bit by bit. In this research a new model of stream cipher SNOW 2.0 has been proposed i.e. Non linear modified SNOW 2.0 using one Linear Feedback Shift Register (LFSR) with the embedding of non linear function in the model. The analysis of Guess and Determined (GD) attack has been done to check its security with respect to previous versions. The proposed model contains one Linear Feedback Shift Register (LFSR) along with the non linear function which increases the strength of the stream cipher, to make the static nature of modified SNOW 2.0 dynamic. The Experimental analysis show that such a mechanism has been built which provides more security than the previous version of modified SNOW 2.0 in which non linearity was either not introduced or it was introduced using two Linear Feedback Shift Registers (LFSRs). It is concluded that this version is more powerful with respect to the security of plain text against Guess and Determined attack (GD) as compared to the previous versions.

In practical communication applications, the channels for intended users and eavesdroppers are not error-free and Wyner’s wiretap channel model deals with the scenario. Using this model, the security of a stand-alone stream cipher can be strengthened by exploiting the properties of physical layer. In this paper, a joint channel coding and light weight cryptography for setting a Gaussian wiretap channel is proposed. The scheme is based on a keyed Quasi Cyclic Low Density Parity Check (QCLDPC) encoder and light weight stream cipher based on Linear Feedback Shift Register (LFSR). The significant contribution is that, highly complex non-linear function that provides security in a Non-Linear Filter Generator (NLFG) is replaced by a simple non-linear function without compromising security. Enhanced security with lesser complexity is achieved by embedding security in channel encoder. Results show that attacker cannot extract the secret key because of the errors introduced in the physical layer due to unknown structure of the channel encoder.

Internet of Things (IoT) is a rapidly developing technology that enables “devices” to communicate and share information amongst them without human control. The devices have the features of internet connectivity and networking. Due to the increasing demands of a secure environment in IoT application, security has become a crucial aspect on which researchers have been increasingly focused. Connecting devices to the internet can facilitate intruders to attack devices as they can access the data from anywhere in the globe. In this work, an encryption–decryption process-based stream cipher has been used. The messages between IoT nodes were encrypted using One Time Pad (OTP) and DNA computing. Furthermore, the required key sequence was generated using a linear feedback shift register (LFSR) as a pseudo number key generator. This key sequence was combined to generate a unique key for each message. The algorithm was implemented using source python and tested on a Raspberry pi under Linux open operation system.

The fast correlation attack described by Meier and Staffelbach (1989) on certain classes of stream ciphers, based on linear feedback shift registers, requires that the number of taps of the characteristic polynomial must be small-typically less than 10. The attack can be extended to characteristic polynomials with an arbitrary number of taps if it is possible to compute low-weight polynomial multiples of the feedback polynomial. In this paper we present an algorithm for the efficient computation of low-weight parity checks. The algorithm, based on the theory of cyclic block error-correcting codes, applies the ideas underlying majority-logic decoding of maximal-length codes. A statistical analysis shows that it is not realistic to consider weight-3 parity checks, and hence it is necessary to compute weight-4 parity checks. The proposed algorithm has a worst-case computational complexity of O(2/sup 2k/3/), which is essentially independent of the number of taps of the characteristic polynomial, and is suitable for linear feedback shift registers of approximately 100 bits.

Recent proposals for keystream generators for stream ciphers based on linear feedback shift registers (LFSRs) incorporate irregular clocking to provide resistance against the conventional correlation attacks. This paper presents a survey of recent attacks, including correlation attacks, on several such keystream generators. These results demonstrate that despite the use of irregular clocking, such generators may still be vulnerable to certain divide and conquer attacks.

Transmission of images on the network is considered insecure which has security-related issues. In this paper, to provide security to digital images, an encryption system that uses four chaotic maps for binary key sequence generation is proposed. The system consists of stages namely, confusion, generation of random binary chaotic key sequence, pseudo-random number generation (RN), and diffusion. Keys for encryption are chosen randomly based on a pseudo random generator from the selected chaotic maps by the linear feedback shift register (LFSR). The algorithm achieves good results in terms of NPCR, UACI, and entropy values. The developed cryptosystem resists differential attacks, is sensitive to minor alterations in the keys, and has a large key space.

Enhancements of a clock-controlled running key generator

When Lagged Fibonacci Generators jump

Linear Feedback Shift Register (LFSRs) based pseudo-random number generators (PRNGs) are used in test pattern generators (TPGs). Because FPGAs are reprogrammable, you can implement designs of LFSR on FPGA and simulate different lengths. It is important to test and validate the simulated results and synthesis results. The primitive polynomial determines the total number of pseudo-random output states of LFSRs. If the polynomial used is a primitive, the output random state is up to 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sup> - 1 state. This paper presented the designed, developed, and implemented 4, 8, 16, and 32 bit reversible LFSRs in FPGAs by performing, analyzing, and investigating random behavior using the Verilog HDL code. The analysis is performed to find the design speed requirements in FPGA when the number of constant inputs, the number of garbage outputs, the number of reversible logic gates, and the increased number of bits. In this paper, shows a comparative study of 4, 8, 16, and 32 bit reversible LFSRs on FPGAs to understand their performance. According to the results, the proposed reversible LFSR design using the Pareek gate approach reduces power by 10% when compared to the irreversible approach. As a result, the proposed design is used to develop Built-In-Self-Test (BIST) module.