Kablolu iletişim ağlarında yeni bir şifreleme tabanlı güvenlik uygulaması

06.03.2018 tarihli ve 30352 sayılı Resmi Gazetede yayımlanan “Yükseköğretim Kanunu İle Bazı Kanun Ve Kanun Hükmünde Kararnamelerde Değişiklik Yapılması Hakkında Kanun” ile 18.06.2018 tarihli “Lisansüstü Tezlerin Elektronik Ortamda Toplanması, Düzenlenmesi ve Erişime Açılmasına İlişkin Yönerge” gereğince tam metin erişime açılmıştır.Günümüzde haberleĢme teknolojileri hızla geliĢmekte ve güvenli iletiĢim önemli bir kavram olarak ortaya çıkmaktadır. Gerek askeri gerek sivil uygulamalar da yapılan bir görüĢmenin, düĢmanın ya da ticari bir rakibin eline geçmemesi için kullanılan ve geliĢtirilen birçok güvenli haberleĢme sistemi mevcuttur. Bu sistemler üzerindeki çalıĢmalar günümüzde hala güncelliğini korumaktadır. Ġnternet ortamında, uydu haberleĢmesinde, telsiz haberleĢmesinde, kablolu telefon hatları ve mobil telefonlarda bu teknolojiler kullanılmakta ve yeni teknikler geliĢtirilmektedir. Bu çalıĢmada Public Switched Telephone Network (PSTN) üzerinden güvenli haberleĢme için bir sistem tasarlanmıĢ ve gerçekleĢtirilmiĢtir. KonuĢma sinyali dijital sinyale çevrilip Ģifrelendikten sonra bir dial up modem aracılığıyla PSTN üzerinden alıcıya gönderilmektedir. Burada Ģifreleme için düĢük bellek ve iĢlem kapasitesine sahip sistemler için geliĢtirilmiĢ SEA ve XTEA algoritmaları kullanılmıĢtır. GerçekleĢtirilen sistem ile konuĢma sinyali Ģifrelenmeden önce bu sinyalin üzerine bir metin gizlenebilmektedir ve bu sayede sistemin güvenliği arttırılmıĢtır. Metin dosyası ses sinyali üzerine gömüldüğünde ses sinyalindeki bozulmaların kulakla algılanmayacak seviyede olmasına dikkat edilmiĢtir. Hattı dinleyen yetkisiz kiĢiler Ģifrelemeyi çözüp ses sinyalini elde etseler bile ses içindeki gizlenmiĢ veriyi algılayıp steganaliz yöntemleri ile elde etmeleri gerekmektedir. Ayrıca yapılan ikinci bir uygulamada, kısa aralıklarla Ģifreleme algoritmaları ile bu algoritmaların kullandıkları anahtarları değiĢtirilmiĢ ve bu değiĢimlerle ilgili bilgiler alıcı ile eĢ zamanlı çalıĢmanın sağlanması için gizli metin içinde gönderilmiĢtir. Böylece Ģifrenin kırılıp yapılan gizli haberleĢmenin içeriğinin elde edilmesi daha da zorlaĢtırılmıĢ ve sistem güvenliği arttırılmıĢtır.Today, communication technologies are developing rapidly and secure communication appears to be an important concept. There are many secure communication systems developed and used for protecting any conversation from an enemy or a trade rival in both military and civil applications. The works performed for these systems still remain up to date today. In the internet, the satellite communication, the radio communication, the wired telephone lines and the mobile phones, these technologies are being used and new techniques are being developed. In this work, a system for secure communication over Public Switched Telephone Network (PSTN) has been designed and realized. After the speech signal is converted to digital signal, the digital signal is encrypted and it is sent to receiver over PSTN by the dial-up modem. The SEA and XTEA algorithms which have been developed for low memory and process capacity, have been used for the encryption. With the developed system, before the encryption of the speech signal, a text can be hide into the signal. So the security of the system has been increased. When the text is embedded to the speech signal, it has been considered that the distortions in the signal are in unsensiblelevel fort he ears. Even if unauthorized persons listening the line can decrypt the encryption and obtain the speech signal, they have to detect and obtain the hidden data in the signal by using the steganalysis methods. In addition, the encryption algorithms and the keys of them have been changed in short periods and the information related with the changes has been sent in the hidden text for synchronization with the receiver. Thus, it is become harder to decrypt the encryption and to obtain the context of the hidden communication and the security of the system is increased

Recent Advances in Steganography

Steganography is the art and science of communicating which hides the existence of the communication. Steganographic technologies are an important part of the future of Internet security and privacy on open systems such as the Internet. This book's focus is on a relatively new field of study in Steganography and it takes a look at this technology by introducing the readers various concepts of Steganography and Steganalysis. The book has a brief history of steganography and it surveys steganalysis methods considering their modeling techniques. Some new steganography techniques for hiding secret data in images are presented. Furthermore, steganography in speeches is reviewed, and a new approach for hiding data in speeches is introduced

Secure covert communications over streaming media using dynamic steganography

Streaming technologies such as VoIP are widely embedded into commercial and industrial applications, so it is imperative to address data security issues before the problems get really serious. This thesis describes a theoretical and experimental investigation of secure covert communications over streaming media using dynamic steganography. A covert VoIP communications system was developed in C++ to enable the implementation of the work being carried out. A new information theoretical model of secure covert communications over streaming media was constructed to depict the security scenarios in streaming media-based steganographic systems with passive attacks. The model involves a stochastic process that models an information source for covert VoIP communications and the theory of hypothesis testing that analyses the adversary‘s detection performance. The potential of hardware-based true random key generation and chaotic interval selection for innovative applications in covert VoIP communications was explored. Using the read time stamp counter of CPU as an entropy source was designed to generate true random numbers as secret keys for streaming media steganography. A novel interval selection algorithm was devised to choose randomly data embedding locations in VoIP streams using random sequences generated from achaotic process. A dynamic key updating and transmission based steganographic algorithm that includes a one-way cryptographical accumulator integrated into dynamic key exchange for covert VoIP communications, was devised to provide secure key exchange for covert communications over streaming media. The discrete logarithm problem in mathematics and steganalysis using t-test revealed the algorithm has the advantage of being the most solid method of key distribution over a public channel. The effectiveness of the new steganographic algorithm for covert communications over streaming media was examined by means of security analysis, steganalysis using non parameter Mann-Whitney-Wilcoxon statistical testing, and performance and robustness measurements. The algorithm achieved the average data embedding rate of 800 bps, comparable to other related algorithms. The results indicated that the algorithm has no or little impact on real-time VoIP communications in terms of speech quality (< 5% change in PESQ with hidden data), signal distortion (6% change in SNR after steganography) and imperceptibility, and it is more secure and effective in addressing the security problems than other related algorithms