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How many combinations of keys can be constructed from a 72 ciphertext stream cipher?(a) 4271(b) 7345(c) 3291(d) 2556The question was asked at a job interview.Asked question is from Cryptography in chapter Number Theory and Cryptography of Discrete Mathematics

Answer» CORRECT answer is (d) 2556

For EXPLANATION: For stream cipher, if there are N ciphertexts then there are n*(n−1)/2 combination of KEYS to be made.

= \(72*\frac{72-1}{2}\)

= 72*35.5

= 2556.


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