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:
“A onetime 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