Final answer:
The length of the key in a One-time Pad is random. It must be the same or longer than the message length and used only once. The One-time Pad's security relies on the randomness and secrecy of the key.
Step-by-step explanation:
The length of the key in a One-time Pad is B. Random.
A One-time Pad is a cryptography system that is theoretically secure. For a One-time Pad to be secure, it must meet several criteria: the key must be truly random, at least as long as the message to be encrypted (meaning the key length is often the same as the message length), used only once (hence 'one-time'), and kept completely secret. If these conditions are met, the One-time Pad can be proven to be unbreakable.
Therefore, the key length is not restricted to a fixed size but varies and should be equal to or longer than the length of the message that needs to be encrypted. This is what makes the One-time Pad different from many other encryption methods that have fixed key lengths, such as those that utilize 56 kb, 64 kb, or 128 kb keys.