One-time pad

The one-time pad has a more complex origin than commonly acknowledged. While credit typically goes to Gilbert Vernam and Joseph Mauborgne for WWI-era work, Frank Miller—a Sacramento banker—described the technique 35 years earlier in 1882, publishing "Telegraphic Code to Insure Privacy and Secrecy."

The modern implementation began in 1917 when Gilbert Vernam, an AT&T Bell Labs engineer, invented an automated cipher system for teleprinter messages. His breakthrough, detailed in U.S. Patent 1,310,719, used XOR operation on Baudot code pulses, enabling on-line encryption without human intervention. The NSA called this patent "perhaps one of the most important in the history of cryptography." Captain Joseph Mauborgne of the Army Signal Corps made the critical refinement: the key tape must be completely random and non-repeating.

Claude Shannon, also at Bell Labs, formally proved in 1941 that the one-time pad is theoretically unbreakable. The security derives from four requirements: key at least as long as plaintext, truly random key, key never reused, key kept completely secret. When met, every possible message is equally probable from the ciphertext.

Despite perfect security, practical challenges limit use. The key distribution paradox: if a secure channel exists to distribute the key, it could transmit the message itself. True randomness requires physical processes like radioactive decay. Key material scales catastrophically for large networks. Key reuse is catastrophic—the Venona project exploited Soviet pad reuse to expose atomic spies.

Cold War applications included the Moscow-Washington Hotline, established August 30, 1963 after the Cuban Missile Crisis. Norwegian-built ETCRRM II cipher machines used one-time pads—each superpower prepared its own key tapes delivered via embassy. Neither had to reveal top-secret systems since the equipment was commercially available. Properly used, it was unbreakable.

Today, one-time pads remain in extremely high-security diplomatic communications where secure key distribution via courier or quantum key distribution is feasible.