1
$\begingroup$

1) Consider the chosen-plaintext attack on the simple substitution cipher. How many chosen plaintext characters suffice to uniquely determine the key?

My answer was: 26!

2) Consider the chosen-ciphertext attack on the simple substitution cipher. How many chosen ciphertext characters suffice to uniquely determine the key?

My answer was: 2 over 26.

3) Using a brute force approach, roughly how many keys would need to be searched on average before guessing the key of the simple substitution cipher? How would one detect that the correct key has been guessed?

My answer was: more than 177 years at 2 over 56 keys/seconds.

4) Consider the chosen-plaintext attack on the simple affine cipher. How many chosen plaintext characters suffice to uniquely determine the key?

My answer was: 26

5) Consider the chosen-ciphertext attack on the simple affine cipher. How many chosen ciphertext characters suffice to uniquely determine the key?

My answer was: 2 over 26.

6) Using a brute force approach, roughly how many keys would need to be searched on average before guessing the key of the simple substitution cipher? How would one detect that the correct key has been guessed?

These questions asked me in the exam, but after the exam I could not find the correct answer and did not understand how to find the results? I really want to learn the reason behind it and correct answers. Thank you.

$\endgroup$
  • 2
    $\begingroup$ It would be helpful if you could also briefly describe the reasoning that led you to those answers. That way, we can see where the wrong answers actually went wrong, and also check that you found the right answers through correct reasoning, and not just by luck. $\endgroup$ – Ilmari Karonen Aug 1 '18 at 9:08
  • $\begingroup$ I think you forgot to change Q6 after copying the text from Q3. $\endgroup$ – Maarten - reinstate Monica Mar 19 at 1:15

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.