Q3 (1 point). Suppose you actually forgot the key. How many decryption computations
✓ Kizspy. me of the cipher text "QNGWFWD" do you need to perform to reach to the plaintext?
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Q4 (1 point). Using the Columnar Transposition Cipher with the same key [4213],
what is the ciphertext for the plaintext SEEYOUATTHELIBRARY? (Leave the unfilled
matrix as blank).
Q5 (1 point). Euler totient function of n (we use the Greek symbol phi to denote Euler
totient function) is the number of positive integers that are between 1 and n - 1,
inclusive, and are relatively prime to n. What is the Euler totient function of 108?
Q6 (1 point). Using the same notations as in the lecture, e.g., p and q are the two
primes and e and d are the public key and the private key, respectively, p = 5, q = 13, e
= 5. What is the value of phi(n) where phi(n) is the Euler Totient Functionof n and n is
the modulus of RSA cipher?
Q7 (1 point). Using the same notations as in the lecture, e.g., p and q are the two
primes and e and d are the public key and the private key, respectively, p = 5, q = 13, e
= 5. Using the phi(n) that you found in the question 6 and the Extended Euclidean
algorithm yields d = 29. What is the ciphertext C when encrypting M = 35?
Q8 (1 point). Using the same notations as in the lecture, e.g., p and q are the two
primes and e and d are the public key and the private key, respectively, p = 5, q = 13
and e=5. The attacker performs a chosen-ciphertext attack (CCA). It has a known
ciphertext 19 and wants to retrieve the corresponding plaintext. It computes c' = c*r^e
mod n and chooses the ciphertext 19*243 mod 65 = 2 and retrieves the corresponding
plaintext, 32. What is the plaintext corresponding to the ciphertext 19?
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