Cryptographic milestones: Origins, modern algorithms, and the quantum era

Cryptography has played a pivotal role in securing communication across human history. From ancient techniques such as hieroglyphic substitutions and Caesar's cipher to contemporary cryptographic systems like RSA and Elliptic Curve Cryptography, the field has continuously adapted to evolving technological paradigms. This article provides a comprehensive review of the historical development of cryptography, highlighting key milestones from ancient Egypt and Mesopotamia, through the mechanical encryption devices of World War II, to the theoretical foundations established by Claude Shannon. It examines the revolutionary introduction of public-key cryptography and follows developments into the digital era, where blockchain technology and privacy innovations like Zero-Knowledge Proofs have expanded cryptographic applications beyond traditional security roles. The article also explores emerging challenges and innovations, particularly those involving artificial intelligence and quantum computing, considering the implications of quantum threats and the ongoing global efforts to develop quantum-resistant encryption standards.