This book, Cyber Security: Principles, Practices, and Applications, is crafted to provide a clear and structured understanding of the key domains of cyber security. It spans foundational concepts, cryptographic techniques, system and application security, and modern-day cyber threats. Each chapter is designed to offer both theoretical knowledge and practical insights, making the content accessible and relevant for students, educators, IT professionals, and enthusiasts. Whether used for academic study or professional reference, this book serves as a reliable guide to building secure systems and developing robust cyber defense strategies in an increasingly digital world.