One-time pad

An encryption method that combines each plaintext symbol with a truly random key symbol used only once. With a secret key at least as long as the message, it provides perfect secrecy.

Exclusive OR: A binary operation that returns 1 when its inputs differ and 0 when they match. Bit-based one-time pads use this operation to combine plaintext and key, then reverse it during decryption.
Plaintext: Readable or otherwise unencrypted information supplied as input to encryption. These are the symbols the pad combines with its random key.
Gilbert Vernam: An American engineer who developed a telegraph cipher combining message characters with key characters. His 1917 cipher supplied the mechanism later associated with the one-time pad.
Moscow–Washington hotline: A communications link established between the United States and the Soviet Union after the Cuban Missile Crisis. Its teletype messages used one-time-pad encryption supported by exchanged key material.
Perfect secrecy: A security property in which ciphertext provides no information about the plaintext, even to an observer with unlimited computing power. The one-time pad is the canonical construction satisfying this strongest information-theoretic guarantee.
Shannon's perfect secrecy: A security property in which observing ciphertext does not change the probability distribution of possible plaintexts. It formally states the guarantee achieved when the one-time pad's key conditions hold.
Cryptographic key: A value that controls the operation of a cryptographic algorithm. The one-time pad's key differs from practical cipher keys because it must match the message's length.
Joseph Mauborgne: A U.S. Army cryptographer who proposed using a truly random key only once with the Vernam cipher. His one-use random-key condition turns Vernam's construction into a pad with perfect secrecy.
Cold War espionage: Covert intelligence activity conducted by rival states during the Cold War. Espionage agencies used pads when secure, low-volume communication justified carrying large quantities of key material.
Computational security: Security based on the infeasibility of solving a problem with available computational resources. Modern practical encryption usually accepts computational assumptions to avoid the pad's enormous key-distribution burden.

Linked from 8 pages