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:
Reference:
“A one-time pad is an extremely powerful type of substitution cipher. One-time pads use a different
alphabet for each letter of the plaintext message.
Normally, one-time pads are written as a very long series of numbers to be plugged into the
function.
The great advantage to one-time pads is that, when used properly, they are an unbreakable
encryption scheme. There is no repeating pattern of alphabetic substitution, redering cryptanalytic
efforts useless. However, several requirements must be met to ensure the integrity of the
algorithm:
The encryption key must be randomly generated. Using a phrase or a passage from a book would
introduce the possibility of cryptanalysts breaking the code.
The one-time pad must be physically secured against disclosure. If the enemy has a copy of the
pad, they can easily decrypt the enciphered messages.
Each one-time pad must be used only once. If pads are reused, cryptanalysts can compare
similarities in multiple messages encrypted with the same pad and possibly determine the key
values used.
The key must be at least as long as the message to be encrypted. This is because each key
element is used to encode only one character of the message.
Pg. 304-305 Tittel: CISSP Study Guide