Comparison between RSA and CAST-128 with Adaptive Key for Video Frames Encryption with Highest Average Entropy

يقوم تشفير البيانات بترجمة البيانات إلى شكل أو رمز آخر يتيح للأشخاص فقط الوصول إلى المفتاح السري أو يمكن قراءة كلمة المرور. يشار إلى البيانات المشفرة عمومًا باسم النص المشفر، بينما يمكن أن تُعرف البيانات غير المشفرة النص الصريح. يمكن استخدام الإنتروبيا كمقياس يعطي عدد البتات التي يمكن أن تكون مطلوبة لتشفير بيانات الصورة. نظرًا لأن قيم البكسل داخل الصورة يتم توزيعها من خلال مستويات رمادية أخرى ، فإن الانتروبيا تزداد. الهدف من هذا البحث هو المقارنة بين طرق التشفير CAST-128 و RSA لإطارات الفيديو لتحديد الطريقة الأكثر دقة مع أعلى إنتروبيا. يتم تحقيق الطريقة الأولى من خلال تطبيق "طريقة CAST-128" ويتم تحقيق الطريقة الثانية من خلال تطبيق "طريقة RSA". يستخدم CAST-128 زوجًا من المفاتيح الفرعية لكل دوره كمقدار من خمسة بتات تم استخدامها كمفتاح دوران لكل دوره وكمية 32 (بت) تم استخدامها كمفتاح إخفاء في الدوره. يمكن استخراج المفتاح المتكيف المقترح ذات 128 بت من القطر الرئيسي لكل إطار قبل التشفير RSA هي تقنية تشفير ذات مفتاح علم يمكن أن تُعرف باسم التشفير (غير المتماثل). يعتمد عدم تناسق المفتاح على تحليل حاصل ضرب قيمتين أوليتين كبيرتين. تم تطبيق المقارنة على العديد من مقاطع الفيديو وأظهرت النتائج أن طريقة CAST-128 أثبتت أعلى درجة من الانتروبيا حتى لو كانت الإطارات تحتوي على الكثير من البيانات المشوهة أو وحدات بكسل الصورة غير الواضحة. على سبيل المثال، قيمة الانتروبيا لعينة فيديو فتاة هي 2581.921 عند استخدام طريقة CAST-128، بينما تكون 2271.329 عند استخدام RSA؛ كما أن قيمة الانتروبيا لعينة فيديو سكوتر هي 2569.814 عند استخدام CAST-128 ، بينما تبلغ 2282.844 عند استخدام RSA.Encryption of data is translating data to another shape or symbol which enables people only with an access to the secret key or a password that can read it. The data which are encrypted are generally referred to as cipher text, while data which are unencrypted are known plain text. Entropy can be used as a measure which gives the number of bits that are needed for coding the data of an image. As the values of pixel within an image are dispensed through further gray-levels, the entropy increases. The aim of this research is to compare between CAST-128 with proposed adaptive key and RSA encryption methods for video frames to determine the more accurate method with highest entropy. The first method is achieved by applying the "CAST-128" and the second is achieved by applying the "RSA ". CAST-128 utilizes a pair of sub-keys for each round as a quantum of  five bits that was utilized as a key of rotation for each round and a quantum of 32 (bits) was utilized as a key of masking into a round . The proposed adaptive 128-bits key can be extracted from the main diagonal of each frame before encryption. RSA is a public-key cryptographic technique which can be known as (asymmetric) cryptography. An asymmetry of a key depends on factoring a product of two big prime values. A comparison was applied on several videos and the results showed that CAST-128 method proved the highest degree of entropy even if the frames have lots of distorted data or unclear image pixels. For example, the entropy value of a sample of a girl video is 2581.921 when using CAST-128, while it is 2271.329 when using the RSA; also the entropy value of a sample of a scooter video is 2569.814 when using the CAST-128, while it is 2282.844 when using RSA

Linear Cryptanalysis of DES with Asymmetries

Linear cryptanalysis of DES, proposed by Matsui in 1993, has had a seminal impact on symmetric-key cryptography, having seen massive research efforts over the past two decades. It has spawned many variants, including multidimensional and zero-correlation linear cryptanalysis. These variants can claim best attacks on several ciphers, including PRESENT, Serpent, and CLEFIA. For DES, none of these variants have improved upon Matsui\u27s original linear cryptanalysis, which has been the best known-plaintext key-recovery attack on the cipher ever since. In a revisit, Junod concluded that when using $2^{43}$ known plaintexts, this attack has a complexity of $2^{41}$ DES evaluations. His analysis relies on the standard assumptions of right-key equivalence and wrong-key randomisation. In this paper, we first investigate the validity of these fundamental assumptions when applied to DES. For the right key, we observe that strong linear approximations of DES have more than just one dominant trail and, thus, that the right keys are in fact inequivalent with respect to linear correlation. We therefore develop a new right-key model using Gaussian mixtures for approximations with several dominant trails. For the wrong key, we observe that the correlation of a strong approximation after the partial decryption with a wrong key still shows much non-randomness. To remedy this, we propose a novel wrong-key model that expresses the wrong-key linear correlation using a version of DES with more rounds. We extend the two models to the general case of multiple approximations, propose a likelihood-ratio classifier based on this generalisation, and show that it performs better than the classical Bayesian classifier. On the practical side, we find that the distributions of right-key correlations for multiple linear approximations of DES exhibit exploitable asymmetries. In particular, not all sign combinations in the correlation values are possible. This results in our improved multiple linear attack on DES using 4 linear approximations at a time. The lowest computational complexity of $2^{38.86}$ DES evaluations is achieved when using $2^{42.78}$ known plaintexts. Alternatively, using $2^{41}$ plaintexts results in a computational complexity of $2^{49.75}$ DES evaluations. We perform practical experiments to confirm our model. To our knowledge, this is the best attack on DES

Multivariate Profiling of Hulls for Linear Cryptanalysis

Extensions of linear cryptanalysis making use of multiple approximations, such as multiple and multidimensional linear cryptanalysis, are an important tool in symmetric-key cryptanalysis, among others being responsible for the best known attacks on ciphers such as Serpent and present. At CRYPTO 2015, Huang et al. provided a refined analysis of the key-dependent capacity leading to a refined key equivalence hypothesis, however at the cost of additional assumptions. Their analysis was extended by Blondeau and Nyberg to also cover an updated wrong key randomization hypothesis, using similar assumptions. However, a recent result by Nyberg shows the equivalence of linear dependence and statistical dependence of linear approximations, which essentially invalidates a crucial assumption on which all these multidimensional models are based. In this paper, we develop a model for linear cryptanalysis using multiple linearly independent approximations which takes key-dependence into account and complies with Nyberg’s result. Our model considers an arbitrary multivariate joint distribution of the correlations, and in particular avoids any assumptions regarding normality. The analysis of this distribution is then tailored to concrete ciphers in a practically feasible way by combining a signal/noise decomposition approach for the linear hulls with a profiling of the actual multivariate distribution of the signal correlations for a large number of keys, thereby entirely avoiding assumptions regarding the shape of this distribution. As an application of our model, we provide an attack on 26 rounds of present which is faster and requires less data than previous attacks, while using more realistic assumptions and far fewer approximations. We successfully extend the attack to present the first 27-round attack which takes key-dependence into account