تشفير الصور بسرية عالية من خالل دمج أنظمة أرقام عشوائية مختلفة

Abstract

t In the last three decades, taking images and sending images has become a daily activity among people due to the massive spread of smartphones equipped with digital cameras, webcams, professional digital cameras. Unauthorized and illegal users should not have the capability of viewing or reaching such images in any means, and some cases become more critical when it comes to critical fields such as politics, military, health care providers. Therefore, exchanged images need to be transformed in a well-managed, secure and reliable manner. PRNG algorithm is the most widely used in image encryption. PRNG is useful in practice because it is repeatable and generates numbers quickly. This algorithm does not depend on a random source, but on mathematical computation, that exposes the image encryption to a violation in the encryption detection. The decisive factor in encryption strength depends mainly on choosing a strong PRNG, for the characteristics of the PRNG to be statistically strong. There is some limitation in existing works, such as a building encryption system on a statistically weak random number generator or using the default PRNG algorithm which is inadequate for encrypting images resulting in easy detection of the encryption key. This study addresses the limitations of the existing image cryptography methods by following and studying a logical method through analysis, comparison, and improvement. Initially, we analyzed PRNG usages by performing various statistical measurements on the encrypted RGB and grayscale images and investigated the performance through manual comparison. Then, we expanded the analysis focusing on one type of image encryption and applied the analysis to the encrypted image to measure the image properties, the strength of the encryption, and keys. Therefore, we implemented a system that automatically measures the performance effectiveness of each PRNG by executing cost-effectiveness calculations as the basis for further work. The details of these experiments and the results obtained led us to choose and define the deterministic effective method for encrypting images using an effective PRNG. finally, we proposed a system to solve the security issue by encrypting images based on the effective PRNG chosen. This proposed algorithm aims to increase the level of security in digital image transmission by improving defects in generators. Our proposed system focuses on effective keystream generation using a chaotic gravitational search algorithm to select random PRNGs in the starting encryption key, followed by a binary gravitational search algorithm to produce the initial value for the selected generator. The proposed image encryption assures three security standards: content integrity, authenticity, and confidentiality. These features achieved the intended aims by increasing the security level and decreasing the probability of discovering the encryption key by external adversaries. Experimentation of the proposed method is applied by using MATLAB 2019. To test the validity of the performance of the proposed image encryption, various test measures are applied, like the visual testing, the statistical testing such as the histogram, the entropy, the Mean Square Error (MSE) and the Peak Signal to Noise Ratio (PSNR). All of these tests have given results indicating that this proposed image encryption is feasible and practical, where encryption and decryption were done successfully and efficiently