Which of the following is not required for a one-time-pad to be unbreakable?

A.
The characters must be truly random

B.
The pads must be secure

C.
The pads must not be reused

D.
Each pad must be unique

Explanation:
Answer D is correct; one-time pads are created as pairs of unique pads. If each individual pad was unique, there would be no way to decrypt a message.

Incorrect Answers and Explanations: A, B, and C: Answers A, B, and C are incorrect. All three are required for a one-time-pad to be unbreakable.