Correlation Properties of Combiners with Memory in Stream Ciphers (Extended Abstract)

In recent years, almost all systems using linear feedback shift storage device (LFSR) design of stream ciphers have been cracked by Algebraic attack. In light of this, finding a modern cipher that avoids old security issues with design of both security and performance becomes an important issue. In 2004, European Union initiated the selection of a new streaming secret (eSTREAM), which is analogous to United States’ formulation of AES block density standards. Forty eight candidates were chosen after public screening, review and final selection process. Details were published in May 2008 results report. This article is to discuss eSTREAM stream cipher. eSTREAM was part of group of eight surviving third phase of software selection process focusing on HC stream cipher for research. In recent years, stream cipher attack studies have been very popular, especially employing Distinguishing Attack. This article also performed security analysis for HC stream cipher, and proposes a design for a reduced version of HC-256. The reduced version of HC-256 is comparable to original HC-256 in terms of resistance to distinguishing attacks. This new generation of core stream cipher algorithm design can help understand implications of theory and application of mathematical practices towards research and analysis of stream ciphers.

Recent lightweight hardware-based stream cipher designs keep an external non-volatile internal state that is not part of the cipher’s hardware module. The purpose of these so-called small-state ciphers is to keep the size of the hardware and the power consumption low. We propose a random oracle model for stream ciphers. This will allow us to analyse the recent small-state stream cipher designs’ resistance against generic attacks and, in particular, time-memory-data tradeoff attacks. We analyse the conventional construction underlying stream ciphers like Grain and Trivium, constructions continuously using the external non-volatile secret key during keystream generation like Sprout, Plantlet, Fruit, and Atom, constructions continuously using the external non-volatile IV, and constructions using a combination of the IV and the key like DRACO. We show the tightness of all bounds by first presenting the time-memory-data tradeoff attacks on the respective constructions, establishing the upper bound on security, and then presenting the proof of security to establish the lower bound on security. In this work, we extend the theoretical work done by Hamann et al. who introduced the DRACO stream cipher at FSE 2023. We use the same random oracle model as the aforementioned work and apply it to the earlier work by Hamann et al. presented at SAC 2019, which showed security for two of the four constructions we consider in this work. Our model is equivalent but allows for a much simpler proof of security. Furthermore, we provide a proof of security for stream ciphers continuously using the secret key during keystream generation, giving upper and lower bounds for all four generic stream cipher constructions proposed so far.

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.

Feedback with Carry Shift Registers (FCSRs) are a promising alternative to LFSRs in the design of stream ciphers. The previous constructions based on FCSRs were dedicated to hardware applications [3]. In this paper, we will describe X-FCSR a family of software oriented stream ciphers using FCSRs. The core of the system is composed of two 256-bits FCSRs. We propose two versions: X-FCSR-128 and X-FCSR-256 which output respectively 128 and 256 bits at each iteration. We study the resistance of our design against several cryptanalyses. These stream ciphers achieve a high throughput and are suitable for software applications (6.3 cycles/byte).Keywordsstream cipherFCSRssoftware designcryptanalysis

Stream cipher is an important device of the GSM system. A secure stream cipher is based on the secure key generator. Lo and Chen proposed a new key generator for the GSM network. Based on the basic architecture of their key generator, they designed three stream ciphers for different security levels of the GSM network. They claimed that the output of their key generator has a long period and satisfies randomness. Consequently, they claimed that the stream ciphers are secure. This paper shows that their key generator and stream ciphers have some weakness. Their stream cipher architectures are not secure.

An adaptive color image encryption scheme using chaotic generalized Arnold map is proposed. The three base color components of the plain-image with 256 grayscale levels are decomposed into 6 parts: 3 higher bit-planes parts and 3 lower bit-planes parts. The intensity values of all these 6 parts are summed to get one secrete key used to scramble the resulted 6 matrices by sort-based approach in a cross way. Chaotic sequences produced by one generalized Arnold map are applied to diffuse the scrambled three base color components crossly as well to get more encryption effects. An adaptive strategy is adopted in both the scrambling process and diffusion process, implying that the key streams are all related to the content of the plain-image. Therefore the image encryption scheme shows strong robustness against known/chosen plaintext attacks. Other performances are carried out, such as key sensitivity, histogram, correlation coefficients, information entropy and difference attack analysis. All the experimental results show that the proposed scheme is secure and effective for practical application.

Time-memory-data (TMD) tradeoff attacks limit the security level of many classical stream ciphers to the birthday bound. Very recently, a new field of research has emerged, which searches for so-called small-state stream ciphers that try to overcome this limitation. In this paper, existing designs and known analysis of small-state stream ciphers are revisited and new insights on distinguishers and key recovery are derived based on TMD tradeoff attacks. A particular result is the transfer of a generic distinguishing attack suggested in 2007 by Englund et al. to this new class of lightweight ciphers. Our analysis shows that the initial hope of achieving full security against TMD tradeoff attacks by continuously using the secret key has failed. In particular, we provide generic distinguishers for Plantlet and Fruit with complexity significantly smaller than that of exhaustive key search. However, by studying the assumptions underlying the applicability of these attacks, we are able to come up with a new design idea for small-state stream ciphers, which might allow to finally achieve full security against TMD tradeoff attacks. Another contribution of this paper is the first key recovery attack against the most recent version of Fruit. We show that there are at least 264 weak keys, each of which does not provide 80-bit security as promised by designers.

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.

The security protocols used in ZigBee rely on an advanced encryption standard-counter mode (AES-CTR) algorithm to encrypt data before transmission. This algorithm is very robust, but it is time consuming. For some industrial and medical applications, it does not meet the real-time requirement. When the AES is used in counter mode CTR, it becomes like a stream cipher that aims to generate pseudorandom bits. Also, to encrypt data, the latter are combined with the plaintext using the XOR operation. New fast stream ciphers were proposed for the eStream project, but these ciphers have shown some weakness. On the other hand, ciphers based on chaotic functions seem to be more promising. Detailed analyses have shown that chaotic functions have very good cryptographic properties and can be used to construct high speed and strong stream ciphers. In this paper, a new robust and fast chaotic encryption algorithm RFCA is presented. This consists of a chaotic cipher composed of two perturbed maps piecewise linear chaotic map. This algorithm is, in particular, adequate for data encryption in ZigBee networks where robustness and real time are both essential. A comparison between our algorithm (RFCA) and the AES-CTR, the simplified AES, and the eStream finalist candidates, is presented with regard to speed and robustness. This is done using correlation coefficients, unified average changing intensity, number of pixels change rate, and test of randomness for the generated bit sequences using the National Institute of Standards and Technology statistical test suite.

The new information and communication technologies require adequate security. In the past decades ,we have witnessed an explosive growth of the digital storage and communication of data ,triggered by some important breakthroughs such as the Internet and the expansive growth of wireless communications. In the world of cryptography ,stream ciphers are known as primitives used to ensure privacy over communication channel and these are widely used for fast encryption of sensitive data. Lots of old stream ciphers that have been formerly used no longer be considered secure ,because of their vulnerability to newly developed cryptanalysis techniques. Many designs stream ciphers have been proposed in an effort to find a proper candidate to be chosen as world standard for data encryption. From these designs, the stream ciphers which are Trivium,Edon80 and Mickey are implemented in ‘c’ language with out affecting their security .Actually these algorithms are particularly suited for hardware oriented environments which provides considerable security and efficiency aspects. We will be targeting hardware applications, and good measure for efficiency of a stream cipher in this environment is the number of key stream bits generated per cycle per gate. For good efficiency we are approaching two ways .One approach is minimizing the number of gates.The other approach is to dramatically increase the number of bits for cycle. This allows reducing the clock frequency at the cost of an increased gate count. Apart from the implementation the analysis which includes the security of these algorithms against some attacks related to stream ciphers such as guess and deterministic attacks, correlation attacks, divide and conquer attacks and algebraic attacks are presented.

Recently, many chaos-based stream cipher algorithms have been developed. Traditional chaos stream cipher is based on XORing a generated secure random number sequence based on chaotic maps (e.g. logistic map, Bernoulli Map, Tent Map etc.) with the original image to get the encrypted image, This type of stream cipher seems to be vulnerable to chosen plaintext attacks. This paper introduces a new stream cipher algorithm based on dynamic substitution box. The new algorithm uses one substitution box (S-box) and a chaotic shuffling process. Each byte in the plain image vector is substituted using a different S-box to get the cipher image vector. This algorithm is designed to be invulnerable to chosen plaintext attacks. In addition, this algorithm is more secured compared to conventional stream cipher.

Feed-forward model is a basic pseudo random sequence generator (PRSG) using in stream cipher. A novel feed-forward model is constructed. Inversion attack on feed-forward model is analysed and detailed inversion attack algorithms and complexity of these algorithms are given, design advice on being resistant to inversion attack is presented on the basis of complexity analysis.The random attributions of the generated number are test with regards to period, balance, correlation and run property. And the result shows that the random number generator generates numbers with very good randomness.

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.

We sought to compare in-office physical exam findings via standing cough test (SCT) versus 24-hour pad weights among men seeking treatment for postprostatectomy stress urinary incontinence (SUI). A retrospective review of a single surgeon database of incontinence procedures was performed. Documentation of SUI severity (grades 0-4) was completed by SCT preoperatively utilizing the Male Stress Incontinence Grading Scale (MSIGS). All patients had pads per day (PPD) and 24-hour pad weights obtained. We determined the Spearman's correlation coefficient between these variables. We identified 104 men who underwent anti-incontinence surgery (AdVance Sling or artificial urinary sphincter [AUS]). In the sling group (65 patients), nearly all (97%) had minimal incontinence with SCT (MSIGS = 0-2). In the AUS group (39 patients), most patients (69%) had an MSIGS 3 or 4 with SCT. Spearman's coefficient between quantification of SCT and pad weight for the overall group was ρ = .68 (P < .0001) demonstrating a strong positive correlation. PPD was also strongly correlated with pad weight (ρ = .55, P < .0001). As seen previously, SCT and PPD were correlated (ρ = .47, P < .0001). In a multivariable model predicting pad weight, the effect of SCT was greater than PPD (β = 83 [54-111], P < .0001 vs 45 [2169], P = .0004). SCT findings strongly correlate to 24-hour pad weights in the evaluation of male SUI. The SCT shows promise as a rapid, reliable, noninvasive measure of SUI severity before anti-incontinence surgery.

Background: Height is one of the data in the forensic identification process. The process of measuring height will be difficult if the bones or body parts found are not intact. Estimation of height can be facilitated by measuring the dimensions of long bones, one of which is the humerus. Analysis of the correlation of humerus bone length with height can support in determining the formula for estimating height based on humerus bone length. This study aims to determine the correlation between humerus bone length and Batak tribe height at HKBP Nommensen University, Medan.&#x0D; Method: This research was a descriptive analytic study with cross sectional design. The research sample was 72 students, lecturers, and employees consisting of 27 men and 45 Batak tribe women who met the inclusion and exclusion criteria at HKBP Nommensen University, Medan. Sampling is done by purposive sampling. Data analysis in this study was carried out by means of univariate and bivariate analysis using the Pearson and Spearman test methods to determine the correlation between humerus bone length variables and height variables.&#x0D; Result: The results obtained there is a strong correlation between humerus bone length and height in the Batak tribe with a correlation coefficient value r = 0.784 (p &lt;0.05). Based on gender, men have weak and insignificant correlation strength with correlation coefficient r = 0.449 (p&gt; 0.05) while women have strong and significant correlation r = 0.771 (p &lt;0.05).&#x0D; Conclusion: There is a strong correlation between humerus bone length and Batak tribal height at HKBP Nommensen University, Medan.