This lecture delves into the evolution of modern cryptography, starting with the milestones such as the Visionary Cipher introducing secret keys, the shift from secret algorithms to secret keys, and the impact of Shannon's information theory. The lecture explores the Diffie-Hellman results, the standardization of encryption methods, and the transition from military to civilian encryption standards. It emphasizes the limitations of information theory in practical cryptography and the importance of complexity theory in assessing security. The lecture also covers the Vernam cipher, the Kirchhoff's principle, and the fundamental problems of data authentication, confidentiality, and integrity.