Rojas, Omar
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Preferred name
Rojas, Omar
Official Name
Rojas Altamirano, Omar Guillermo
Alternative Name
orojas
Main Affiliation
ORCID
Scopus Author ID
22954196800
Researcher ID
K-1066-2013

Research Output
Now showing 1 - 9 of 9
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Publication

Selecting an Effective Entropy Estimator for Short Sequences of Bits and Bytes with Maximum Entropy

2021 , Lianet Contreras Rodríguez , Evaristo José Madarro-Capó , Carlos Miguel Legón-Pérez , Rojas, Omar , Sosa-Gómez, Guillermo

Entropy makes it possible to measure the uncertainty about an information source from the distribution of its output symbols. It is known that the maximum Shannon’s entropy of a discrete source of information is reached when its symbols follow a Uniform distribution. In cryptography, these sources have great applications since they allow for the highest security standards to be reached. In this work, the most effective estimator is selected to estimate entropy in short samples of bytes and bits with maximum entropy. For this, 18 estimators were compared. Results concerning the comparisons published in the literature between these estimators are discussed. The most suitable estimator is determined experimentally, based on its bias, the mean square error short samples of bytes and bits.

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A New Family of Boolean Functions with Good Cryptographic Properties

2021 , Sosa-Gómez, Guillermo , Octavio Paez-Osuna , Rojas, Omar , Evaristo José Madarro-Capó

In 2005, Philippe Guillot presented a new construction of Boolean functions using linear codes as an extension of the Maiorana–McFarland’s (MM) construction of bent functions. In this paper, we study a new family of Boolean functions with cryptographically strong properties, such as non-linearity, propagation criterion, resiliency, and balance. The construction of cryptographically strong Boolean functions is a daunting task, and there is currently a wide range of algebraic techniques and heuristics for constructing such functions; however, these methods can be complex, computationally difficult to implement, and not always produce a sufficient variety of functions. We present in this paper a construction of Boolean functions using algebraic codes following Guillot’s work.

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Measuring Independence between Statistical Randomness Tests by Mutual Information

2020 , Jorge Augusto Karell-Albo , Carlos Miguel Legón-Pérez , Evaristo José Madarro-Capó , Rojas, Omar , Sosa-Gómez, Guillermo

The analysis of independence between statistical randomness tests has had great attention in the literature recently. Dependency detection between statistical randomness tests allows one to discriminate statistical randomness tests that measure similar characteristics, and thus minimize the amount of statistical randomness tests that need to be used. In this work, a method for detecting statistical dependency by using mutual information is proposed. The main advantage of using mutual information is its ability to detect nonlinear correlations, which cannot be detected by the linear correlation coefficient used in previous work. This method analyzes the correlation between the battery tests of the National Institute of Standards and Technology, used as a standard in the evaluation of randomness. The results of the experiments show the existence of statistical dependencies between the tests that have not been previously detected.

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Improvements in the computing efficiency of the probabilities of the LIL test for the PRNG evaluation

2022 , Yuniel Matos-Rodríguez , Evaristo José Madarro-Capó , Carlos Miguel Legón-Pérez , Rojas, Omar , Guillermo Sosa-Gómez

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Measuring Avalanche Properties on RC4 Stream Cipher Variants

2021 , Evaristo José Madarro-Capó , Carlos Miguel Legón-Pérez , Rojas, Omar , Sosa-Gómez, Guillermo

In the last three decades, the RC4 has been the most cited stream cipher, due to a large amount of research carried out on its operation. In this sense, dissimilar works have been presented on its performance, security, and usability. One of the distinguishing features that stand out the most is the sheer number of RC4 variants proposed. Recently, a weakness has been reported regarding the existence of statistical dependence between the inputs and outputs of the RC4, based on the use of the strict avalanche criterion and the bit independence criterion. This work analyzes the influence of this weakness in some of its variants concerning RC4. The five best-known variants of RC4 were compared experimentally and classified into two groups according to the presence or absence of such a weakness.

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Construction of Boolean Functions from Hermitian Codes

2022 , Sosa-Gómez, Guillermo , Octavio Paez-Osuna , Pedro Luis del Ángel Rodríguez , Rojas, Omar , Herbert Kanarek , Evaristo José Madarro-Capó

In 2005, Guillot published a method for the construction of Boolean functions using linear codes through the Maiorana–McFarland construction of Boolean functions. In this work, we present a construction using Hermitian codes, starting from the classic Maiorana–McFarland construction. This new construction describes how the set of variables is divided into two complementary subspaces, one of these subspaces being a Hermitian Code. The ideal theoretical parameters of the Hermitian code are proposed to reach desirable values of the cryptographic properties of the constructed Boolean functions such as nonlinearity, resiliency order, and order of propagation. An extension of Guillot’s work is also made regarding parameters selection using algebraic geometric tools, including explicit examples.

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Practical Improvement in the Implementation of Two Avalanche Tests to Measure Statistical Independence in Stream Ciphers

2024 , Evaristo José Madarro-Capó , Eziel Christians Ramos Piñón , Sosa-Gómez, Guillermo , Rojas, Omar

This study describes the implementation of two algorithms in a parallel environment. These algorithms correspond to two statistical tests based on the bit’s independence criterion and the strict avalanche criterion. They are utilized to measure avalanche properties in stream ciphers. These criteria allow for the statistical independence between the outputs and the internal state of a bit-level cipher to be determined. Both tests require extensive input parameters to assess the performance of current stream ciphers, leading to longer execution times. The presented implementation significantly reduces the execution time of both tests, making them suitable for evaluating ciphers in practical applications. The evaluation results compare the performance of the RC4 and HC256 stream ciphers in both sequential and parallel environments.

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Information Theory Based Evaluation of the RC4 Stream Cipher Outputs

2021 , Evaristo José Madarro-Capó , Carlos Miguel Legón-Pérez , Rojas, Omar , Sosa-Gómez, Guillermo

This paper presents a criterion, based on information theory, to measure the amount of average information provided by the sequences of outputs of the RC4 on the internal state. The test statistic used is the sum of the maximum plausible estimates of the entropies H(jt|zt), corresponding to the probability distributions P(jt|zt) of the sequences of random variables (jt)t∈T and (zt)t∈T, independent, but not identically distributed, where zt are the known values of the outputs, while jt is one of the unknown elements of the internal state of the RC4. It is experimentally demonstrated that the test statistic allows for determining the most vulnerable RC4 outputs, and it is proposed to be used as a vulnerability metric for each RC4 output sequence concerning the iterative probabilistic attack.

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Bit Independence Criterion Extended to Stream Ciphers

2020 , Evaristo José Madarro-Capó , Carlos Miguel Legón-Pérez , Rojas, Omar , Sosa-Gómez, Guillermo , Raisa Socorro-Llanes

The bit independence criterion was proposed to evaluate the security of the S-boxes used in block ciphers. This paper proposes an algorithm that extends this criterion to evaluate the degree of independence between the bits of inputs and outputs of the stream ciphers. The effectiveness of the algorithm is experimentally confirmed in two scenarios: random outputs independent of the input, in which it does not detect dependence, and in the RC4 ciphers, where it detects significant dependencies related to some known weaknesses. The complexity of the algorithm is estimated based on the number of inputs l, and the dimensions, n and m, of the inputs and outputs, respectively.

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