Cryptography and Network Security in the Modern Era is a comprehensive guide that explores the foundational and advanced aspects of securing digital systems. The book begins by introducing the basics of cryptography, tracing its historical evolution and practical applications. It progresses to cover classical and modern cryptographic techniques, providing readers with a balanced understanding of theory and practice. Key topics include classical ciphers, modern encryption algorithms like DES, AES, and RSA, as well as hash functions and data integrity mechanisms. The book also delves into network security principles, addressing threats such as malware, phishing, and DoS attacks, and explaining protective measures like firewalls, intrusion detection systems, and VPNs. Furthermore, it discusses advanced topics such as Public Key Infrastructure (PKI) and the role of cryptography in blockchain and cryptocurrency technologies. With its clear structure and emphasis on practical relevance, this book is suitable for students, IT professionals, and anyone interested in the field of cybersecurity. By bridging the gap between theoretical knowledge and practical application, it equips readers to address modern security challenges effectively.