DEVELOPMENT & ANALYSIS OF CRYPTOGRAPHIC SCHEMES FOR VISUAL CONTENT

Abstract

The unprecedented advancement in technology, usage of internet and mobile services along with the upsurge of social networking as an indispensable part of day to day life, has brought forth an unimaginable necessitate for voluminous data transfer over inherently insecure networks. Also, there has been a significant shift in the type of transmitted digital content. The transmissions are no more limited to text-based data; they contain significant amounts of multimedia-based content of which visual content like images form a major part. Further, the emergence of Internet of Things (IoT) as a new reality is leading to significant increase in the multimedia traffic, including visual content, on penetrable networks. Traditional symmetric ciphers like AES, DES, IDEA etc. have been focusing on securing textual data, and are not found suitable for meeting the special resource efficiency requirements and catering the intrinsic properties of redundancy and bulkiness of visual content like images. It has been largely observed that while designing encryption schemes for securing visual content like images, the focus of researchers has been limited largely on one of the two key aspects pivotal to securing visual content i.e. cost efficiency and strength, thereby compromising on the other. Therefore, a need is identified for lightweight solution to secure visual content with complete removal of redundancy for real-time and resource constrained environments. In the proposed research work, unconventional approaches have been employed to design lightweight encryption schemes many of which have customizable properties to suit the requirements of the specific applications to create balance between desired level of security and efficiency. New chaos-based cryptographic primitives are proposed and are used for customization of standard block ciphers like AES and lightweight block cipher like PRESENT to make them suitable for securing visual content. Also, a conditional encryption based block cipher is customized for its suitability to secure visual content like images. Further, the probabilistic approach has been extended for designing a symmetric image encryption scheme with customizable block size whereby the cipher image generated for the same key and for the same plain image differs each time the plain image is encrypted. Next, use of dynamic encryption has been proposed where by though the encryption scheme is deterministic yet chaos-based dynamism depending on the key and plaintext has been introduced at multiple levels so that cryptanalysis becomes much difficult for an adversary because in absence of knowledge of key, the adversary will not know the exact structure of the encryption process being used for encrypting a particular plaintext. Security analysis has been performed for proving the strength of all the proposed schemes and their resistance against cryptanalytic attacks. Lastly, weaknesses in existing chaos-based image encryption schemes reducible to solvable mathematical model are studied. Cryptanalysis on one such scheme proposed by Zhou et al. (2014) was performed to unravel the weaknesses in the design of the said scheme and such similar schemes in general. Improvements are also proposed to improve the strength of the said scheme.