MS, Kent State University, 2024, College of Arts and Sciences / Department of Computer Science

Cryptography, derived from the Greek word meaning "to hide information," involves techniques for converting readable plaintext into unreadable ciphertext through a process called encryption. Cryptography algorithms are broadly categorized into two types: symmetric key cryptography and asymmetric key cryptography. Symmetric key cryptography is further divided into block ciphers and stream ciphers. Block ciphers, based on their structure, can be classified into two main categories: Substitution-Permutation Networks (SPN) and Feistel Networks (FN). This research focuses on SPN-based block ciphers. In 1949[1], Claude Shannon introduced two fundamental operations required for a robust cryptosystem: substitution and permutation. Substitution, the core component of SPN-based cryptography, is implemented through substitution boxes (S-Boxes), where each element in the plaintext is mapped to another element to achieve nonlinearity and provide the confusion property crucial for security. With the rise of constrained devices, such as the Internet of Things (IoT), there is an increasing demand for lightweight symmetric-key algorithms. However, in many cases, the S-Box contributes the most to the hardware complexity and computational load compared to other linear components. This research addresses this challenge by designing and optimizing a lightweight cryptosystem suitable for resource-limited environments. The thesis makes two key contributions to the field of lightweight cryptography. The first contribution is the development of chaos-based S-Boxes tailored for devices with restricted computational capabilities. By leveraging chaotic maps, the proposed S-Boxes achieve a high degree of nonlinearity and security while maintaining a minimal computational and hardware footprint, making them ideal for IoT and other constrained devices. These chaos-based S-Boxes introduce dynamic, unpredictable substitution patterns that enhance resistance to cryptanalysis techniques such as l (open full item for complete abstract)

Committee: Maha Allouzi Dr (Advisor); Younghun Chae Dr (Committee Member); Lei Xu Dr (Committee Member) Subjects: Computer Engineering; Computer Science

MS, University of Cincinnati, 2006, Engineering : Computer Engineering

A majority of group communication applications in cellular-based heterogeneous wireless setups entail secure data exchange. The problem can be effectively tackled if the underlying cellular infrastructure is used to provide an authentication backbone to the security associations. We propose a novel distributed ID based key exchange mechanism using shared polynomials in which the shares are generated by the communicating groups. Our idea employs a mechanism where the Base Stations (BSs) carry out an initial key generation by a polynomial in a distributed manner and then pass on the key material to the Mobile Stations (MSs). The multi-interface MSs can now securely communicate over interfaces other than cellular. The scheme incorporates symmetric polynomials, which are chosen by the BS acting as polynomial distributors. Simulations done to measure performance have shown encouraging results.

Committee: Dr. Agrawal Dharma (Advisor) Subjects: Computer Science

PhD, University of Cincinnati, 2010, Engineering : Computer Science and Engineering

Wireless Mesh Network (WMN) is a promising wireless technology in providing high-bandwidth Internet access over a specific coverage area, with relative lower investment cost as compared to traditional access network. In a WMN, a mobile client (MC) can access the Internet through a wireless backbone formed by wireless Mesh Routers (MRs) which are interconnected in a multi-hop fashion while some MRs known as Internet Gateways (IGWs) act as the communication bridges between the wireless backbone and the Internet. The design of the network architecture is a fundamental issue for a WMN and is critical in determining the network performance and providing Quality of Service (QoS) for end users, and thus should be addressed carefully. A unique characteristic of a WMN is the IGW oriented Internet traffic. Thus, the deployment of IGW is the key problem in the network design, and is investigated in this dissertation. Two IGW oriented network architecture are analyzed, and corresponding QoS requirements and constraints are evaluated. The IGW deployment problem is then formulated as a multiple objectives optimization problem. Besides the linear program approach, some heuristic algorithms are proposed and evaluated. Extensive simulations show the effectiveness of proposed solutions. To improve the performance of a given WMN, load balancing between different IGW domains is also investigated. A fairness between IGWs domains improves the network performance and provides a better QoS for end users. The fairness index is defined for both homogenous and heterogeneous WMNs. A distributed load balancing scheme is proposed, and three load balancing algorithms based on diffusion methodology are introduced in the proposed scheme. Authenticated key establishment (AKE) schemes enable two entities (e.g., a client and a server) to share common communication keys in an authentic way. Due to mobility of mesh clients (MCs), a WMN needs have a fast and efficient authentication and key establishment (open full item for complete abstract)

Committee: Dharma Agrawal DSc (Committee Chair); Kenneth Berman PhD (Committee Member); Chia Han PhD (Committee Member); Kelly Cohen PhD (Committee Member); Ernest Hall PhD (Committee Member) Subjects: Computer Science

PhD, University of Cincinnati, 2005, Arts and Sciences : Mathematical Sciences

I. The Matsumoto-Imai cryptosystem was eventually defeated by Patarin's linearization attack. This attack takes advantage of the special algebraic structure of MI to produce a set of linearization equations that can be used to find the plaintext associated with a given ciphertext. In this paper, we present a solution to the problem of finding the dimension of the space of linearization equations. In particular, we show that this space has dimension in general, and has dimension 2n, 2n/3, 3n/2, 8 or 7 in some exceptional cases. II. We show that for some small prime number p, the group generated by invertible Dickson and linear polynomials over the finite field of p elements Zp is the whole symmetric group over Zp, and consequently any permutation of Zp can be described explicitly in terms of composition of these polynomials. For a general prime number, we study the properties of this group and the properties of the cycles of the permutations generated by Dickson polynomials. We show that the answer to the question, if the group generated by invertible Dickson and linear polynomials over the finite field Zp is the whole symmetric group over Zp, is indeed a non-trivial problem, particularly in terms of computational point of view.

Committee: Jintai Ding (Advisor) Subjects: Mathematics