Exam-style question
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Which statement correctly compares a Vernam cipher with computationally secure ciphers?.
- A.Both have been mathematically proved to be completely secure
- B.A Vernam cipher has perfect security, whereas other ciphers rely on the difficulty of breaking them with available time and resources
- C.Computationally secure ciphers cannot theoretically be broken
- D.A Vernam cipher is secure only when its key is reused
Model answer
What a good answer should say
- A Vernam cipher has perfect security, whereas other ciphers rely on the difficulty of breaking them with available time and resources
Explanation
Why this works
The Vernam cipher is the only cipher in the specification described as mathematically proved to be completely secure. Other ciphers depend on computational security and could theoretically be broken given enough ciphertext and time.
Common mistake
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