One-Time Pad Algorithm

The one-time pad is an encryption algorithm that combines a message with a secret random key of matching length, character by character, using modular addition, so that each symbol of the ciphertext depends on both the original message and an equally long stretch of true randomness. Provided the key is truly random, used only once, kept completely secret and is at least as long as the message itself, the resulting cipher is the only encryption system mathematically proven to be unbreakable under information theory, since a ciphertext produced this way is consistent with every possible message of the same length. Frank Miller first described the underlying idea in 1882, and Gilbert Vernam of AT&T patented an electrical implementation of it, built around an exclusive-or operation, in 1919; a colleague, Joseph Mauborgne, later recognized that using a genuinely random, non-repeating key was what actually made the scheme unbreakable rather than merely difficult to crack. Its practical drawback is the very requirement that makes it secure: safely generating, distributing and never reusing a key as long as every message ever sent is a serious logistical burden.