What uses a key of the same length as the message?

A.
Running key cipher

B.
One-time pad

C.
Steganography

D.
Cipher block chaining

Explanation:
The one time pad is the most secure, and one of the simplest of all cryptographic methods. It was
invented and patented just after World War I by Gilbert Vernam (of AT&T) and Joseph Mauborgne
(USA, later chief of the Signal Corps). The fundamental features are that the sender and receiver
each have a copy of an encryption key, which is as long as the message to be encrypted, and each
key is used for only one message and then discarded. That key must be random, that is without
pattern, and must remain unknown to any attacker. In addition, the key must never be reused,
otherwise the cipher becomes trivially breakable. One of its features it’s the key length, it’s the same
as the message.