1. In cryptography, the one-time pad encrypts data by XORing the plaintext against a stream of truely random bits. In theory, the one-time pad is the only unbreakable encryption algorithm, even with infinite resources or quantum computers. This is because if the key (aka. pad) is totally random, then the ciphertext will be random as well. Problem: While the one-time pad is perfectly secure in theory, it has problems in practice, and is rarely used. The major problem is how one distributes the one-time pads to all the receivers. This can be done in some cases, such as sending out CD-ROMs full of random bits with soldiers on the battle-fields, but it becomes unwieldy for normal uses of cryptography. Key point: The pad (secret key) can be used only once. If it is ever used twice, then much of the plaintext can be easily recovered. This means that the pad must be as long as the data being encrypted. History: The one-time pad was invented by G. S. Vernam in 1926, and saw heavy use during WWII. It is still used today in diplomatic corps, spies, the Washington-Moscow "hot-line". Rumor: There are many short-wave radio stations throughout the world broadcasting a human voice reading off long lists of numbers. These are thought to be messages sent to spies throughout the word who decode them with one-time pads. Key point: Today's encryption algorithm are based upon the theoretical underpinnings of the one-time pad. From Hacking-Lexicon