If implemented properly, a one-time pad is a perfect encryption scheme. Which of the following incorrectly describes a requirement for implementation?

A.
The pad must be securely distributed and protected at its destination.

B.
The pad must be made up of truly random values.

C.
The pad must always be the same length.

D.
The pad must be used only one time.

Explanation:
C: A one-time pad is a perfect encryption scheme because it is considered unbreakable if implemented properly. It was invented by Gilbert Vernam in 1917, so sometimes it is
referred to as the Vernam cipher. The pad must be at least as long as the message. If it is not as long as the message, the pad will need to be reused to cover the whole message.
This would be the same thing as using a pad more than one time, which could introduce patterns.
A is incorrect because it is true that the pad must be securely distributed and protected at its destination. This is a very cumbersome process to accomplish, because the pads are
usually just individual pieces of paper that need to be delivered by a secure courier and properly guarded at each destination. One-time pads have been used throughout history to
protect different types of sensitive data. Today, they are still in place for many types of militaries as a backup encryption option if current encryption processes (that require computers
and a power source) are unavailable for reasons of war or attacks.
B is incorrect because it is true that the pad must be made up of truly random values. This may not seem like a difficult task, but even our computer systems today do not have truly
random number generators; rather, they have pseudorandom number generators. These generators are seeded by an initial value from some component within the computer system
(time, CPU cycles, etc.). Although a computer system is complex, it is a predictable environment, so if the seeding value is predictable in any way, the resulting values created are not
truly randombut pseudorandom.
D is incorrect because it is true that the pad must be used only one time.If the pad is used more than one time, this might introduce patterns in the encryption process that will aid an
evildoer in his goal of breaking the encryption. Although the one-time pad approach to encryption can provide a very high degree of security, it is impractical in most situations because
of all of its different requirements. Each possible pair of entities that might want to communicate in this fashion must receive, in a secure fashion, a pad. This type of key management
can be overwhelming and may require more overhead than it is worth. The distribution of the pad can be challenging, and the sender and receiver must be perfectly synchronized so
that each is using the same pad.