Yazar "Mesut, Andac Sahin" seçeneğine göre listele

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    A Character Based Steganography Using Masked Language Modeling
    (IEEE-Inst Electrical Electronics Engineers Inc, 2024) Ozturk, Emir; Mesut, Andac Sahin; Fidan, Ozlem Aydin
    In this study, a steganography method based on BERT transformer model is proposed for hiding text data in cover text. The aim is to hide information by replacing specific words within the text using BERT's masked language modeling (MLM) feature. In this study, two models, fine-tuned for English and Turkish, are utilized to perform steganography on texts belonging to these languages. Furthermore, the proposed method can work with any transformer model that supports masked language modeling. While traditionally the hidden information in text is often limited, the proposed method allows for a significant amount of data to be hidden in the text without distorting its meaning. In this study, the proposed method is tested by hiding stego texts of varying lengths in cover text of different lengths in two different language scenarios. The test results are analyzed in terms of perplexity, KL divergence and semantic similarity. Upon examining the results, the proposed method has achieved the best results compared to other methods found in the literature, with KL divergence of 7.93 and semantic similarity of 0.99. It can be observed that the proposed method has low detectability and demonstrates success in the data hiding process.
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    Generating binary diffusion layers with maximum/high branch numbers and low search complexity
    (Wiley-Hindawi, 2016) Akleylek, Sedat; Sakalli, Muharrem Tolga; Ozturk, Emir; Mesut, Andac Sahin; Tuncay, Gokhan
    In this paper, we propose a new method to generate n x n binary matrices (for n = k . 2(t) where k and t are positive integers) with a maximum/high of branch numbers and a minimum number of fixed points by using 2(t) x 2(t) Hadamard (almost) maximum distance separable matrices and k x k cyclic binary matrix groups. By using the proposed method, we generate n x n (for n = 6, 8, 12, 16, and 32) binary matrices with a maximum of branch numbers, which are efficient in software implementations. The proposed method is also applicable with m x m circulant matrices to generate n x n (for n = k . m) binary matrices with a maximum/high of branch numbers. For this case, some examples for 16 x 16, 48 x 48, and 64 x 64 binary matrices with branch numbers of 8, 15, and 18, respectively, are presented. Copyright (C) 2016 John Wiley & Sons, Ltd.
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    On the Algebraic Expression of the AES S-Box Like S-Boxes
    (Springer-Verlag Berlin, 2010) Sakalli, M. Tolga; Aslan, Bora; Bulus, Ercan; Mesut, Andac Sahin; Buyuksaracoglu, Fatma; Karaahmetoglu, Osman
    In the literature, there are several proposed block ciphers like ADS, Square, Shark and Hierocrypt which use S-boxes that are based on inversion mapping over a finite field. Because of the simple algebraic structure of S-boxes generated in this way, these ciphers usually use a bitwise affine transformation after the inversion mapping. In some ciphers like Camellia, an additional affine transformation is used before the input of the S-box as well. In this paper, we study algebraic expressions of S-boxes based on power mappings with the aid of finite field theory and show that the number of terms in the algebraic expression of an S-box based on power mappings changes according to the place an affine transformation is added. Moreover, a new method is presented to resolve the algebraic expression of the AES S-box like S-boxes according to the given three probable cases.