Enhancing the Strict Avalanche Criteria for Speech Encryption through Systematic Analysis

The strict avalanche criterion was introduced by Webster and Tavares [] in order to combine the ideas of completeness and the avalanche effect. A cryptographic transformation is complete if each output bit depends on all the input bits, and it exhibits the avalanche effect if an average of one half of the output bits change whenever a single input bit is complemented. To fulfil the strict avalanche criterion, each output bit should change with probability one half whenever a single input bit is complemented. This means, in particular, that there is no good lower order (fewer bits) approximation to the function. This is clearly a desirable cryptographic property since such an approximation would enable a corresponding reduction in the amount of work needed for an exhaustive search.

The Substitution Box (S-box) is a fundamental nonlinear transformation utilized within cryptographic algorithms to map an input bit string into an output bit string. Due to the complexity and variability of cryptographic attacks, constructing S-boxes using traditional methods has proven challenging. However, recent advancements in optimization algorithms have provided new ideas for S-box construction. To address the difficulty of constructing high-performance S-boxes through traditional means, this paper proposes a design for an 8×8 S-box based on the improved sine-cosine algorithm. In this study, genetic algorithm's mutation and crossover operations are incorporated into the sine-cosine algorithm to optimize the initial S-box constructed using the improved Newton iterative method. The resulting S-box is then evaluated based on cryptographic criteria such as bijection, nonlinearity, strict avalanche criterion, bit-independent criterion, linear probability, and differential probability. Comparative analysis with several previous S-box generation methods demonstrates that the proposed S-box design exhibits superior cryptographic properties.

Cryptography deals with designing practical mathematical algorithms having the two primitive elements of confusion and diffusion. The security of encrypted data is highly dependent on these two primitive elements and a key. S-box is the nonlinear component present in a symmetric encryption algorithm that provides confusion. A cryptographically strong bijective S-box structure in cryptosystem ensures near-optimal resistance against cryptanalytic attacks. It provides uncertainty and nonlinearity that ensures high confidentiality and security against cryptanalysis attacks. The nonlinearity of an S-box is highly dependent on the dispersal of input data using an S-box. Cryptographic performance criteria of chaos-based S-boxes are worse than algebraic S-box design methods, especially differential probability. This article reports a novel approach to design an 8 × 8 S-box using chaos and randomization using dispersion property to S-box cryptographic properties, especially differential probability. The randomization using dispersion property is introduced within the design loop to achieve low differential uniformity possibly. Two steps are involved in generating the proposed S-box. In the first step, a piecewise linear chaotic map (PWLCM) is utilized to generate initial S-box positions. Generally, the dispersion property is a post-processing technique that measures maximum nonlinearity in a given random sequence. However, in the second step, the concept is carefully reverse engineered, and the dispersion property is used within the design loop for systematic dispersal of input substituting sequence. The proposed controlled randomization changes the probability distribution statistics of S-box’s differentials. The proposed methodology systematically substitutes the S-box positions that cause output differences to recur for a given input difference. The proposed S-box is analyzed using well-established and well-known statistical cryptographic criteria of nonlinearity, strict avalanche criteria (SAC), bit independence criteria (BIC), differential probability, and linear probability. Further, the S-box’s boomerang connectivity table (BCT) is generated to analyze its strength against boomerang attack. Boomerang is a relatively new attacking framework for cryptosystem. The proposed S-box is compared with the state-of-the-art latest related publications. Results show that the proposed S-box achieves an upper bound of cryptographic properties, especially differential probability. This work hypothesizes that highly dispersive hamming distances at output difference, generated a systematic S-box. The mixing property of chaos generated trajectories utilized for decimal mapping. To test the randomness of generated chaotic trajectories, a cryptographically secure pseudo-random sequence was generated using a chaotic map that was tested using the National Institute of Standards and Technology (NIST) NIST-800-22 test suit.

Stream ciphers are highly frequent in the realm of secret key cryptography because of their low-computational complexity and latency. Though variety of attack models for testing the robustness of various stream ciphers are available, the differential fault analysis (DFA) model is the most popular. DFA is used not only to disclose the identity of any unknown cipher but also to recover the secret KEY and the cipher’s internal state. Deep learning approaches extract patterns from large amounts of cryptographic data, which aids in crypt-analysis. Here, single bit and multi-bit faults are injected into the internal register of trivium cipher, and artificial neural network (ANN) is used to identify the injected fault location without any handcrafted features of keystream unlike other existing state-of-the-art fault analysis techniques. In order to enhance the speed of fault analysis, we have used system on chip (SoC) platform where ANN-based classifier has been placed in the programmable logic area as an accelerator. This enhances the speed of fault analysis by 9% for single bit fault, 12% for two adjacent bit faults, and 13% for three adjacent bit faults compared to their software models. To the best of the author’s knowledge, this is the first of kind research where ANN-based hardware accelerator has been used for fault location identification on SoC platform.

The substitution boxes are the only components in most of symmetric encryption systems that induce nonlinearity to provide efficacious data confusion. The cryptographic potency of these systems primarily depends upon the caliber of their S-boxes. This brings new challenges to design cryptographically efficient S-boxes to develop strong encryption systems. Here, a simple and effective method to design an efficient 8×8 S-box is put forward. The proposed design methodology is based on the classical Fisher-Yates shuffle technique. A piece-wise linear chaotic map is incorporated to act as a source to generate random numbers for proficient execution of shuffle technique. The construction of dynamic S-box is under the control of secret key. The performance evaluation of proposed S-box against standard statistical tests like bijective property, nonlinearity, strict avalanche criteria and equiprobable I/O XOR distribution reveals its excellent performance. Moreover, the proposed S-box is also compared with some recent chaos-based S-boxes. The investigations confirm that the design is consistent and suitable for secure communication.KeywordsFisher-Yates shufflesubstitution-boxchaotic mapnonlinearitysecure communication

In wireless communication systems, the conventional secret key exchange is based on the public key cryptography, which requires complex computations to retain the secrecy level of these key bits. The proposed physical layer-based algorithms have shown promising performance to extract secret keys from the privately shared randomness relying on the reciprocal channel state between both communicated nodes. In this study, the authors propose a physical layer key exchange method which transmits the key bits by encoding them within some phase randomisation (PR) sequences that are privately indexed to a specific channel criterion. The PR sequences only randomise the data phases and thus no efficiency reduction will be incurred. In fact, by choosing a pool of randomisation sequences with certain statistical properties, they could also be used to condition the signal to meet physical layer transmission requirements such as bandwidth, envelope and so on. They quantify the potential of the proposed method by demonstrating it within the context of a multiple-input multiple-output orthogonal frequency division multiplexing system. The results reveal that, relative to existing techniques, the proposed method offers superior key error rate performance at lower computational complexity with better secrecy level.

This paper introduces a new encryption method for a block cipher. To keep the ciphertext safe, traditional methods usually use secret keys in simple fixed logic operations. To break the cipher, cryptanalysis has been developed. They use stochastic characteristics such as differential and linear relationships between the input and output data. Encryption algorithms must be secure against these analyses. The proposed method uses the secret key to modify substitution tables called S-Boxes in the encryption algorithm. They are reconfigured on demand using FPGA. Our method is hard enough to prevent the encrypted data from analyzing the secret key using statistical cryptanalysis.

A probabilistic version of the Bernstein-Vazirani problem (which is a generalization of the original Bernstein-Vazirani problem) and a quantum algorithm to solve it are proposed. The problem involves finding one or more secret keys from a set of multiple secret keys (encoded in binary form) using a quantum oracle. From a set of multiple unknown keys, the proposed quantum algorithm is capable of (a) obtaining any key (with certainty) using a single query to the probabilistic oracle and (b) finding all keys with a high probability (approaching 1 in the limiting case). In contrast, a classical algorithm will be unable to find even a single bit of a secret key with certainty (in the general case). Owing to the probabilistic nature of the oracle, a classical algorithm can only be useful in obtaining limiting probability distributions of $ 0 $ and $ 1 $ for each bit-position of secret keys (based on multiple oracle calls) and this information can further be used to infer some estimates on the distribution of secret keys based on combinatorial considerations. For comparison, it is worth noting that a classical algorithm can be used to exactly solve the original Bernstein-Vazirani problem (involving a deterministic oracle and a single hidden key containing $n$ bits) with a query complexity of $\mathcal{O}(n)$. An interesting class of problems similar to the probabilistic version of the Bernstein-Vazirani problem can be construed, where quantum algorithms can provide efficient solutions with certainty or with a high degree of confidence and classical algorithms would fail to do so.

In this paper, we introduce the Kirchhoff-Law-Johnson-Noise (KLJN) as an approach to securing satellite communications. KLJN has the potential to revolutionize satellite communication security through its combination of simplicity, cost-effectiveness, and resilience with unconditional security. Unlike quantum key distribution (QKD), which requires complex, fragile, and expensive infrastructure like photon detectors and dedicated optical links, KLJN operates using standard electronic components and wires, significantly reducing implementation costs and logistical hurdles. KLJN’s security, grounded in the fundamental laws of classical physics, is impervious to environmental and radiation-induced noise, making it highly reliable in the harsh conditions of satellite communications. This robustness, coupled with its ability to integrate seamlessly with existing infrastructure, positions KLJN as a revolutionary alternative to quantum solutions for ensuring secure, resilient satellite communications. The authors explore the value of achieving unconditionally secure communications in strategic ground-to-satellite networks which address vulnerabilities posed by advanced computational threats, including quantum computing. Our team has examined two leading approaches to unconditional security — the KLJN scheme and QKD — and analyzed the potential use of each for space systems. While QKD leverages quantum mechanics for security, it faces challenges related to cost, complexity, and environmental sensitivity. In contrast, the KLJN scheme utilizes classical physics principles to provide a simpler, more cost-effective, and resilient alternative, particularly for ground-based systems. Further, this paper highlights the potential for complementary roles of these technologies in hybrid networks: KLJN can facilitate secure key exchanges without QKD for ground communications connected via wire, and QKD could facilitate secure inter-island and direct-to-satellite communications. Through a detailed analysis of implementation challenges, key exchange speeds, and network architectures, this study concludes that KLJN offers significant advantages in simplicity, cost-efficiency, and robustness, making it a practical choice for many secure communication applications.

Metal–organic frameworks (MOFs) enable the design of host–guest systems with specific properties. In this work, we show how the confinement of anthracene in a well‐chosen MOF host leads to reversible yellow‐to‐purple photoswitching of the fluorescence emission. This behavior has not been observed before for anthracene, either in pure form or adsorbed in other porous hosts. The photoresponse of the host–guest system is caused by the photodimerization of anthracene, which is greatly facilitated by the pore geometry, connectivity, and volume as well as the structural flexibility of the MOF host. The photoswitching behavior was used to fabricate photopatternable and erasable surfaces that, in combination with data encryption and decryption, hold promise in product authentication and secure communication applications.

We present an entangled-state quantum cryptography system that operated for the first time in a real-world application scenario. The full key generation protocol was performed in real-time between two distributed embedded hardware devices, which were connected by 1.45 km of optical fiber, installed for this experiment in the Vienna sewage system. The generated quantum key was immediately handed over and used by a secure communication application.

In recent years, chaotic systems have begun to take a substantial place in literature due to increasing importance of secure communication. Chaotic synchronization which has emerged as a necessity for secure communication can now be performed with many different methods. This study purposes the Master-Slave synchronization via active controller and real time simulation of five different chaotic systems such as Lorenz, Sprott, Rucklidge, Moore-Spiegel, Rössler. Master slave synchronization was performed because of synchronization realized between the same type of chaotic systems with different initial parameters and also because of the systems were expected to behave similarly as a result of synchronization. Active control method was used to amplify the difference signal between master and slave systems which have different initial parameters and to return back synchronization information to the slave system. The real time simulation and synchronization of the master and slave systems performed successfully in LabVIEW environment. Furthermore, for the real time implementation, analogue outputs of NI-DAQ card used and real time results also were observed on an oscilloscope and secure communication application using sinusoidal signal and an image encryption application achieved successfully.

This paper reports a new 3-dimensional autonomous chaotic system with four nonlinearities. The system is studied with respect to its numerical solutions in phase space, including sensitive dependence on initial conditions, equilibrium points, bifurcation, and maximal Lyapunov exponent. It is shown that the system is dissipative and has a fractional Lyapunov dimension. Besides, a basin of attraction is determined by the Newton–Raphson’s method. To show its practicality, the new system is implemented by means of an analog electronic circuit. Aperiodicity of the experimental signal is verified by means of an improved power spectral density estimator, viz., the Welch’s method. Also, the correlation dimension is estimated from the experimental time series with the result confirming that the responses are deterministic chaos. Finally, an electronic design of a secure communication application is carried out, wherein a nontrivial square wave is modulated by a master chaotic signal. The modulated signal is subsequently recovered by a slave system, and the fast convergence to zero of the information recovery error substantiates the effectiveness of the design.

It has been demonstrated by a number of investigators that there is a relationship between chaotic signals and systems and communications and information theory. In particular, it has been shown that the output sequences of chaotic non-linear dynamic systems can be exploited for encoding information, for modulating waveforms in spread spectrum applications, and for masking information-bearing waveforms in secure communication applications. An information theoretic relationship can be obtained from the concepts of Markov partitions, metric entropy, symbolic dynamics, and topological entropy. >

A robust true random number generator (TRNG), able to assure high quality output at different working conditions, is an attractive solution in secure communication application, because it increases resilience against possible external attacks. Among different TRNGs, quantum RNGs (QRNG) represent a good candidate for such systems, because of their compactness, low cost and performance [1–6]. They typically consist of a source of photons, such as an attenuated LED, coupled to a detector with single photon capability (SPAD). Many works in the literature have used a single detector [1–4] for random bit extraction. These devices are characterized by a limited bit rate [1], which can be increased by exploiting the arrival time of photons at the cost of circuit and system complexity [2–4]. Recent works [5–6] proposed to implement an array of detectors based on SPAD working in parallel thus extending the speed of QRNG up to 5 Gb/s [5]. Despite the high bit rate, the main drawback of [5] is the strong dependence of each pixel bias on the impinging light intensity which forces the system to work only for a narrow range of photon flux that poses several constraints on the design of the final QRNG system, e.g. the need of a feedback control loop to maintain a constant flux of photons, and of a uniform distribution of light over the entire sensor. Moreover, it is impractical to implement algorithms for bit extraction to all detectors of the array because of different responses and mismatches among SPADs.