Exam-style question
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Which condition is essential for a Vernam cipher, or one-time pad, to provide perfect security?.
- A.The key is reused for every message
- B.The key is shorter than the plaintext
- C.The key is chosen uniformly at random and used once only
- D.The key is made from a Caesar shift
Model answer
What a good answer should say
- The key is chosen uniformly at random and used once only
Explanation
Why this works
The specification states that the key must be chosen uniformly at random and used once only. The key is known as a one-time pad, and these conditions support perfect security.
Common mistake
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