Cryptography , the art and science of secret writing , is one of humanity’s oldest tools of security. Throughout history, kings, generals, and diplomats have turned words into numbers, and letters into symbols, to protect their secrets. From the hieroglyphs of ancient Egypt to Julius Caesar’s “Caesar Cipher,” and the complex codes of the Renaissance, this story reveals how deeply the need for secrecy has shaped human civilization. Yet, the true turning point in the history of cryptography cam...