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Q1 (1 point). Given that totient(377) is 336, what is 69^673 (mod 377)?
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Q2 (1 point). You agreed to use a Caesar cipher with a key of k = 7 with a friend. While
sitting in a group, the friend hands you over a message that says "MWABUPCLYZPAF.
Decrypt the message?
Q3 (1 point). Suppose you actually forgot the key. How many decryption computations
of the cipher text "QNGWFWD" do you need to perform to reach to the plaintext?
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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