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.