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Article Cryptographic Randomness Testing of Block Ciphers: SAC Tests(IEEE-Inst Electrical Electronics Engineers Inc, 2026) Aslan, Melis; Doganaksoy, Ali; Kocaman, Sermin; Saygi, Zulfukar; Sulak, FatihBlock ciphers are designed to function as random mappings, making it essential for them to successfully pass statistical randomness tests. These tests evaluate whether the distribution of a test statistic, derived empirically through various data manipulations over states of the algorithm, aligns with the theoretical distribution for cryptographic randomness. Beyond this, evaluating the cryptographic properties of the algorithm is also important to ensure its security and reliability. One of the important cryptographic randomness properties is the Strict Avalanche Criterion (SAC), which assesses the impact of a one-bit alteration in the input over the output. In this work, we introduce new SAC-based tests to offer more reliable evaluation for the cryptographic randomness of block cipher algorithms. The tests are utilized for the application of AES, PRESENT, and CLEFIA block ciphers. The results are compared with Soto's evaluation methods, which are known for their comprehensive approach to block ciphers. According to this, it is apparent that our novel SAC tests improve upon Soto's results, thus providing a more comprehensive understanding of randomness.Article Citation - WoS: 2Citation - Scopus: 1Observations on Nist Sp 800-90b Entropy Estimators(Springer, 2025) Aslan, Melis; Doganaksoy, Ali; Saygi, Zulfukar; Turan, Meltem Sonmez; Sulak, FatihRandom numbers play a crucial role in cryptography since the security of cryptographic protocols relies on the assumption of the availability of uniformly distributed and unpredictable random numbers to generate secret keys, nonce, salt, etc. However, real-world random number generators sometimes fail and produce outputs with low entropy, leading to security vulnerabilities. The NIST Special Publication (SP) 800-90 series provides guidelines and recommendations for generating random numbers for cryptographic applications and describes 10 black-box entropy estimation methods. This paper evaluates the effectiveness and limitations of the SP 800-90 methods by exploring the accuracy of these estimators using simulated random numbers with known entropy, investigating the correlation between entropy estimates, and studying the impacts of deterministic transformations on the estimators.Article Citation - WoS: 1Citation - Scopus: 3LS-14 Test Suite for Long Sequences(Hacettepe Univ, Fac Sci, 2024) Akcengiz, Ziya; Aslan, Melis; Doğanaksoy, Ali; Sulak, Fatih; Uguz, MuhiddinRandom number sequences are used in many branches of science. Because of many techni- cal reasons and their practicality, pseudo random sequences are usually employed in place of true number sequences. Whether a sequence generated through a deterministic process is a pseudo random, in other words, random-looking sequence or it contains certain pat- terns, can be determined with the help of statistics and mathematics. Although, in the literature there are many statistical randomness tests for this purpose, there is no much work on test suites specialized for long sequences, that is sequences of length 1,000,000 bits or more. Most of the randomness tests for long sequences use some mathematical ap- proximations to compute expected values of the random variables and hence their results contain some errors. Another approach to evaluate randomness criteria of long sequences is to partition the long sequence into a collection short sequences and evaluate the collec- tion for the ran- domness using statistical goodness of fit tests. The main advantage of this approach is, as the individual sequences are short, there is no need to use mathematical approximations. On the other hand when the second approach is preferred, partition the long sequence into a collection of fixed length subsequences and this approach causes a loss of information in some cases. Hence the idea of dynamic partition should be included to perform a more reliable test suite. In this paper, we propose three new tests, namely the entire R2 run, dynamic saturation point, and dynamic run tests. Moreover, we in- troduce a new test suite, called LS-14, consisting of 14 tests to evaluate randomness of long sequences. As LS-14 employs all three approaches: testing the entire long sequence, testing the collection of fixed length partitions of it, and finally, testing the collection obtained by the dynamic partitions of it, the proposed LS-14 test suit differs from all existing suites. Mutual comparisons of all 14 tests in the LS-14 suite, with each other are computed. Moreover, results obtained from the proposed test suite and NIST SP800-22 suite are compared. Examples of sequences with certain patterns which are not observed by NIST SP800-22 suite but detected by the proposed test suite are given.Correction Observations on Nist Sp 800-90b Entropy Estimators (Jan, 10.1007/S12095-025-00778-7, 2025)(Springer, 2025) Aslan, Melis; Doganaksoy, Ali; Saygi, Zulfukar; Turan, Meltem Sonmez; Sulak, Fatih
