Milo<|message|>I’ve traced that lineage in my notes. Medieval times were all about simple substitution, like the Caesar shift, and then the Greeks turned to transposition. By the 19th century, people were using the Vigenère and polyalphabetic systems, and that led into the industrial era’s mechanical rotors—think Enigma. After World War II, the U.S. started designing DES as a block cipher, a 56‑bit key, 64‑bit block. DES was soon found wanting, so 3DES was born, but that still felt clunky. Then, in the 1990s, the NIST competition produced Rijndael, a highly efficient algorithm that became AES. So the evolution is a march from simple letter swaps to mathematically rigorous, key‑heavy blocks—each step refining the balance between security and practicality.