Browsing by Author "Kocak, Onur"

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Citation - WoS: 1
Modifications of Knuth Randomness Tests for Integer and Binary Sequences
(Ankara Univ, Fac Sci, 2018) Kocak, Onur; Sulak, Fatih; Doganaksoy, Ali; Uguz, Muhiddin; Mathematics; 02. School of Arts and Sciences; 01. Atılım University
Generating random numbers and random sequences that are indistinguishable from truly random sequences is an important task for cryptography. To measure the randomness, statistical randomness tests are applied to the generated numbers and sequences. Knuth test suite is the one of the first statistical randomness suites. This suite, however, is mostly for real number sequences and the parameters of the tests are not given explicitly. In this work, we review the tests in Knuth Test Suite. We give test parameters in order for the tests to be applicable to integer and binary sequences and make suggestions on the choice of these parameters. We clarify how the probabilities used in the tests are calculated according to the parameters and provide formulas to calculate the probabilities. Also, some tests, like Permutation Test and Max-of-t-test, are modified so that the test can be used to test integer sequences. Finally, we apply the suite on some widely used cryptographic random number sources and present the results.
Citation - WoS: 28
Citation - Scopus: 28
On the Independence of Statistical Randomness Tests Included in the Nist Test Suite
(Tubitak Scientific & Technological Research Council Turkey, 2017) Sulak, Fatih; Uguz, Muhiddin; Kocak, Onur; Doganaksoy, Ali; Mathematics; 02. School of Arts and Sciences; 01. Atılım University
Random numbers and random sequences are used to produce vital parts of cryptographic algorithms such as encryption keys and therefore the generation and evaluation of random sequences in terms of randomness are vital. Test suites consisting of a number of statistical randomness tests are used to detect the nonrandom characteristics of the sequences. Construction of a test suite is not an easy task. On one hand, the coverage of a suite should be wide; that is, it should compare the sequence under consideration from many different points of view with true random sequences. On the other hand, an overpopulated suite is expensive in terms of running time and computing power. Unfortunately, this trade-off is not addressed in detail in most of the suites in use. An efficient suite should avoid use of similar tests, while still containing sufficiently many. A single statistical test gives a measure for the randomness of the data. A collection of tests in a suite give a collection of measures. Obtaining a single value from this collection of measures is a difficult task and so far there is no conventional or strongly recommended method for this purpose. This work focuses on the evaluation of the randomness of data to give a unified result that considers all statistical information obtained from different tests in the suite. A natural starting point of research in this direction is to investigate correlations between test results and to study the independences of each from others. It is started with the concept of independence. As it is complicated enough to work even with one test function, theoretical investigation of dependence between many of them in terms of conditional probabilities is a much more difficult task. With this motivation, in this work it is tried to get some experimental results that may lead to theoretical results in future works. As experimental results may reflect properties of the data set under consideration, work is done on various types of large data sets hoping to get results that give clues about the theoretical results. For a collection of statistical randomness tests, the tests in the NIST test suite are considered. Tests in the NIST suite that can be applied to sequences shorter than 38,912 bits are analyzed. Based on the correlation of the tests at extreme values, the dependencies of the tests are found. Depending on the coverage of a test suite, a new concept, the coverage efficiency of a test suite, is defined, and using this concept, the most efficient, the least efficient, and the optimal subsuites of the NIST suite are determined. Moreover, the marginal benefit of each test, which also helps one to understand the contribution of each individual test to the coverage efficiency of the NIST suite, is found. Furthermore, an efficient subsuite that contains five statistical randomness tests is proposed.
Citation - WoS: 8
Periodic Template Tests: a Family of Statistical Randomness Tests for a Collection of Binary Sequences
(Elsevier, 2019) Sulak, Fatih; Doganaksoy, Ali; Uguz, Muhiddin; Kocak, Onur; Mathematics; 02. School of Arts and Sciences; 01. Atılım University
In this work, we classify all templates according to their periods and for each template we evaluate the exact probabilities using generating functions. Afterwards, we propose a new family of statistical randomness tests, that is periodic template tests, for a collection of binary sequences. We apply these tests to the outputs of AES, SHA-3, SHA-2 family, SHA-1 and MD5 and the binary expansion of pi and root 2 and biased non-random data to test the power of new tests. Moreover, we give the probabilities for all templates for the overlapping template matching test in the NIST test suite. Afterwards, we analyse the power of templates and compare the periodic template tests with NIST overlapping template test. (C) 2019 Elsevier B.V. All rights reserved.
Citation - WoS: 2
Citation - Scopus: 3
R-2 Composition Tests: a Family of Statistical Randomness Tests for a Collection of Binary Sequences
(Springer, 2019) Uguz, Muhiddin; Doganaksoy, Ali; Sulak, Fatih; Kocak, Onur; Mathematics; 02. School of Arts and Sciences; 01. Atılım University
In this article a family of statistical randomness tests for binary strings are introduced, based on Golomb's pseudorandomness postulate R-2 on the number of runs. The basic idea is to construct recursive formulae with computationally tenable probability distribution functions. The technique is illustrated on testing strings of 2(7), 2(8), 2(10) and 2(12) bits. Furthermore, the expected value of the number of runs with a specific length is obtained. Finally the tests are applied to several collections of strings arising from different pseudorandom number generators.
Citation - WoS: 2
A SECOND PRE-IMAGE ATTACK AND A COLLISION ATTACK TO CRYPTOGRAPHIC HASH FUNCTION LUX
(Ankara Univ, Fac Sci, 2017) Sulak, Fatih; Kocak, Onur; Saygi, Elif; Ogunc, Merve; Bozdemir, Beyza; Mathematics; 02. School of Arts and Sciences; 01. Atılım University
Cryptography is a science that provides the security of information in communication. One of the most important sub-branches of cryptography is the hash functions. Hash functions are known as the digital fingerprints. Following the recent attacks on the widely used hash functions MD5 and SHA-1 and the increase in computational power, the need for a new hash function standard has arisen. For this purpose, US National Institute of Standards and Technology (NIST) had announced a competition to select a standard hash function algorithm which would eventually become the Third Secure Hash Algorithm, SHA-3. Initially 64 algorithms were submitted to NIST and 51 of them were announced as the First Round Candidates. After an analysis period, 14 of these algorithms were announced as the Second Round Candidates, and 5 algorithms were announced as Finalists. The winner of the competition, Keccak, was announced in 2012. LUX is one of the 64 algorithms submitted to the SHA-3 competition by Nikolic et al. It is designed as a byte oriented stream cipher based hash function. For LUX-256, Schmidt-Nielsen gave a distinguisher and later Wu et al. presented collision attacks, both of which for reduced rounds of LUX. As a result of these attacks, LUX is eliminated in the first round. In this work, we first give a procedure for the second preimage attack. Then we extend this to the collision and second preimage attacks for the reduced rounds of LUX hash family. Moreover, we implement the attacks and give the specific examples by taking the padding into consideration.