Acta Cybernetica <div id="main-content" class="region clearfix"> <div class="region region-content"> <div id="block-system-main" class="block block-system"> <div class="content"> <div id="node-30" class="node node-page clearfix"> <div class="content"> <div class="field field-name-body field-type-text-with-summary field-label-hidden"> <div class="field-items"> <div class="field-item even"> <p><img style="margin-left: 10px; margin-right: 10px; float: right; width: 203px; height: 291px;" src="" alt=""> A scientific journal published by the <a href="">Institute of Informatics</a>, <a href="">University of Szeged</a>, <a href="">Szeged</a>, <a href="">Hungary</a>.</p> <p>Acta Cybernetica is abstracted by <a href="">Mathematical Reviews</a>, <a href="">Computing Reviews</a>, <a href="">Zentralblatt für Mathematik</a>&nbsp;and <a href=";picked=prox" target="_blank" rel="noopener">ACM Digital Library</a> It is also indexed by <a href="">Scopus</a>,&nbsp;<a href="">DBLP</a>, EBSCO and Emerging Sources Citation Index (ESCI).</p> <p><img src="" alt="">&nbsp;<a href=";tip=sid&amp;clean=0"><img style="width: 200px; height: 200px;" src="" alt=""></a></p> </div> </div> </div> </div> </div> </div> </div> </div> </div> University of Szeged, Institute of Informatics en-US Acta Cybernetica 0324-721X An Information Theoretic Image Steganalysis for LSB Steganography <p>Steganography hides the data within a media file in an imperceptible way. Steganalysis exposes steganography by using detection measures. Traditionally, Steganalysis revealed steganography by targeting perceptible and statistical properties which results in developing secure steganography schemes. In this work, we target LSB image steganography by using entropy and joint entropy metrics for steganalysis. First, the Embedded image is processed for feature extraction then analyzed by entropy and joint entropy with their corresponding original image. Second, SVM and Ensemble classifiers are trained according to the analysis results. The decision of classifiers discriminates cover image from stego image. This scheme is further applied on attacked stego image for checking detection reliability. Performance evaluation of proposed scheme is conducted over grayscale image datasets. We analyzed LSB embedded images by Comparing information gain from entropy and joint entropy metrics. Results conclude that entropy of the suspected image is more preserving than joint entropy. As before histogram attack, detection rate with entropy metric is 70% and 98% with joint entropy metric. However after an attack, entropy metric ends with 30% detection rate while joint entropy metric gives 93% detection rate. Therefore, joint entropy proves to be better steganalysis measure with 93% detection accuracy and less false alarms with varying hiding ratio.</p> Sonam Chhikara Rajeev Kumar Copyright (c) 2020-07-25 2020-07-25 10.14232/actacyb.279174 On the Steps of Emil Post: from Normal Systems to the Correspondence Decision Problem <pre style="-qt-block-indent: 0; text-indent: 0px; margin: 0px;">In 1946, Emil Leon Post (Bulletin of Amer. Math. Soc. 52 (1946), 264-268) introduced his famouscorrespondence decision problem, nowadays known as the Post Correspondence Problem (PCP).Post proved the undecidability of the PCP by areduction from his normal systems. In the presentarticle we follow the steps of Post, and give another, somewhat simpler and more straightforwardproof of the undecidability of the problem by using the same source of reductions as Post did.We investigate these, very different, techniques, and point out out some peculiarities in theapproach used by Post.</pre> Vesa Halava Tero Harju Copyright (c) 2020-07-25 2020-07-25 10.14232/actacyb.284625 Estimating the Dimension Of The Subfield Subcodes of Hermitian Codes <p><span class="fontstyle0">In this paper, we study the behavior of the true dimension of the subfield subcodes of Hermitian codes. Our motivation is to use these classes of linear codes to improve the parameters of the McEliece cryptosystem, such<br>as key size and security level. The McEliece scheme is one of the promising alternative cryptographic schemes to the current public key schemes since in the last four decades, they resisted all known quantum computing attacks. By computing and analyzing a data collection of true dimensions of subfield subcodes, we concluded that they can be estimated by the extreme value distribution function.</span></p> Gábor Péter Nagy Sabira El Khalfaoui Copyright (c) 2020-07-25 2020-07-25 10.14232/actacyb.285453