one time pad

In cryptography, the one-time pad (OTP) is an encryption algorithm in which the plaintext is combined with a secret random key or pad, which is used only once. A modular addition is typically used to combine plaintext elements with pad elements. (For binary data, the operation XOR amounts to the same thing.) It was invented in 1917 and patented a couple of years later. If the key is truly random, never reused in whole or part, and kept secret, the one-time pad provides perfect secrecy. It has also been proven that any cipher with the perfect secrecy property must use keys with effectively the same requirements as OTP keys.^{[citation needed]} The key normally consists of a random stream of numbers, each of which indicates the number of places in the alphabet (or number stream, if the plaintext message is in numerical form) which the corresponding letter or number in the plaintext message should be shifted. For messages in the Latin alphabet, for example, the key will consist of a random string of numbers between 0 and 25; for binary messages the key will consist of a random string of 0s and 1s; and so on.